October 2017 - Power Systems Design · versatile BBU-S is available with AC or DC input voltage and can charge and control multiple battery pack configurations. The BBU-S starts at

October 2017

Special Report: Industrial Power (pg 35)

VIEWpoint

The Return of Industry BringsOpportunity for Designers By Ally Winning, European EditorPower Systems Design

POWERline

ROHM’s New High Resolution Audio SoC Supports a Variety of Sound Sources

NOTABLE&newsworthy

Powerbox’s battery backup unit system reduces railway modernization time

MARKETwatch

3 Key Trends in the Age of Industry 4.0By Kevin Parmenter, PSD Contributor

DESIGNtips

Increasing the Power Density and Efficacy of Datacenters Using a Two-Stage Solution for 48VBy Qian Ouyang, Rohan Samsi and

Jinghai Zhou, Monolithic Power Systems

COVER STORY

High Power Density Systems

Demand High Current Converters

By Steve Knoth, Senior Product Market-ing Engineer and Steve Zhou Senior Design Engineer, Linear Technology, Now Part of Analog Devices

TECHNICAL FEATURES

Power Supplies

Changing Demands for the Power IndustryBy Patrick Le Fevre, Chief Marketing and Communications Officer, Powerbox

Power Supplies

Implementing Tapped Buck Topology By Silvestro Fimiani, Product Marketing Manager, Power Integrations

Passive Components

Resistor Specifications and Howto Interpret Them By Kory Schroeder, Director of Marketing and Product Engineering, Stackpole Electronics

Power Supplies

Benefits of digital controlled programmable AC power sourcesBy Herman van Eijkelenburg, Director of Marketing, Pacific Power

Circuit Protection

Power Protection Starts with Switches By Mike Bolduc, Global Marketing Man-

ager, Industrial & Medical Segments C&K

SPECIAL REPORT:INDUSTRIAL POWER

Intelligent Battery Monitoring

By Steve Applegate, Sales Director, Stadium Stontronics

2

Supercapacitors Come of Age

By Kunio Nomura, Product Manager Capacitors, Murata

Functionality Convergence in IIoT

By Muhammed Shafique, solution architect, Mentor a Siemens company

FINALthought

Small decisions, large consequences By Ally Winning, European EditorPower Systems Design

Dilbert

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Highlighted Products News, Industry News and

more web-only content, to:

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POWER SYSTEMS DESIGN 2017OCTOBER

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48

COVER STORY

High Power Density Systems Demand High Current Converters (pg 10)

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Welcome to the October issue of PSD. This month our focus will be on industrial power. The industrial sector has always been an important focus for electronics designers in Europe, and that demand is continuing to grow as automation becomes more important to industry. But as the industry grows, the demands on designers change. Automation inherently adds intelligence to designs, and the emergence of Industry 4.0 has accelerated this process. At the same time Industry 4.0 demands that devices are smaller, more rugged, wireless capable and use less power.

Using less power overall is a common target of the whole electronics industry, but in Europe the EU has put a special focus on industrial technology. The EU estimates that electrical motors are responsible for almost half of the electricity used on the continent and that more efficient motors could lead to a €700 energy saving over each product’s lifetime. In total, more efficient motors in Europe could save 135 TWh of electricity and avoid over 60 million tonnes of CO2 emissions by 2020.

To ensure those savings, the EU has passed regulation, as part of the Ecodesign directive, that lays out the minimum efficiency for low voltage motors which can be sold in the EU. The legislation initially classified motors into five categories dependant on efficiency and banned the sale of the least efficient in 2011. The next stage of the legislation came into force in 2015 and banned the second lowest efficiency category unless they were powered and controlled by a variable speed drive. Variable speed drives are much more complex, and keep the motors running at the maximum efficiency. This year, the lower limit of the regulations has dropped from 7.5kW to 0.75kW, bringing many more motors into the legislation’s scope.

But, designing power products for industry is not only motors and drives. The industrial sector is also driving innovation for sensors and control systems, as well as rugged wireless technologies. Each of these technologies has its own challenges for designers of power systems. Sensor clusters pose a significant challenge as they will normally be situated away from power sources and have to rely on batteries. These remote locations may also be hard to get access to for maintenance, so battery life is crucial. Other products may not even have room for batteries, and rely on scavaging energy from the environment. These designs will only have access to minute amounts of power to take readings, process them and then transmit the information to the router, which poses a real challenge for the power industry. Especially when the products may have to be protected from hostile environments at the same time.

But, as ever, designers are rising to the challenge. Thanks to them, innovation is coming quickly, bringing technology into the most unusual places and inhospitable environments. At first glance, the industrial sector may not seem to be the most exciting and innovative place for designers, but under the surface, some of the most interesting challenges are being solved.

Best Regards,

Ally Winning European Editor, [email protected]

The Return of Industry

Brings Opportunity

for Designers

Power Systems Corporation 146 Charles Street Annapolis, MD 21401 USA Tel: +410.295.0177Fax: +510.217.3608 www.powersystemsdesign.com Editorial Director Jim Graham [email protected]

Editor - EuropeAlly [email protected]

Editor - North AmericaJason [email protected]

Editor - ChinaLiu [email protected]

Contributing Editors Kevin Parmenter, [email protected]

Publishing DirectorJulia [email protected]

Creative Director Chris [email protected]

Circulation Management Sarah [email protected]

Sales Team Marcus Plantenberg, [email protected]

Ruben Gomez, North America [email protected]

Registration of copyright: January 2004ISSN number: 1613-6365

Power Systems Corporation and Power Systems Design Magazine assume and hereby disclaim any liability to any person for any loss or damage by errors or ommissions in the material contained herein regardless of whether such errors result from negligence, accident or any other cause whatsoever.

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ROHM has recently announced the avail-ability of a high resolution audio SoC,

BM94803AEKU, designed to act as the ‘brain’ in audio applica-tions such as Bluetooth speak-ers, USB DACs, and mini/micro component systems by carrying out control and management of peripheral components and input/output I/F as well as enable playback of a wide range of audio sources.

In recent years, a variety of audio devices are required to faithfully reproduce information from dif-ferent sound sources (media/mu-sic files) – not just high-resolution audio.However, in order to support a wide range of audio sources mul-tiple media decoders are required (i.e. CD, USB, Bluetooth) along with additional peripheral com-ponents, leading to challenges relating to increased software complexity and development load.

For the audio sector ROHM not only offers general-purpose ICs such as opamps, but audio-related ICs as well, ranging from media decoders and speaker amps to sound processors. This

ROHM's New High Resolution Audio SoC Supports a Variety of Sound Sources

time, ROHM developed an audio SoC that acts as the ‘brain’ of audio devices along with a refer-ence design that improves audio quality for the entire system while minimizing development load.

The BM94803AEKU integrates a processor chip with SDRAM fea-turing an optimized architecture that leverages software and circuit elements such as ASIC (Applica-tion Specific IC), MCU, and vari-ous media decoders (developed by the ROHM Group) on a single chip. The media decoder supports a wide range of audio sources, and utilizing over 20 years of expertise allows ROHM to ensure stable playback of damaged CDs

and even non-standard USB. In addition, SDRAM is built in that contributes to greater miniatur-ization.

This SoC allowed ROHM to achieve the industry’s first high-resolution reference audio design. The design maximizes the per-formance of audio devices and peripheral applications by config-uring ROHM’s amp, CD driver, and other elements around the audio SoC. Furthermore, provid-ing dedicated software enables rapid development of audio devices capable of stable playback of a wide range of audio sources, shortening development time considerably.

Powerbox’s battery backup unit system reduces railway modernization time

Powerbox, has the launched its second generation Battery Backup Unit System

to support the modernization of railway networks and industrial applications that require flexible power backup systems with extended monitoring and control. Responding to the needs of a large range of applications and designed for use in enclosed outdoor environments, Powerbox’s BBU-S comprises an industry standard 19-inch rack unit with sub-modules. System-wise, the BBU-S includes an active power factor corrected input, micro controlled smart charging, automatic battery test, output distribution and several control and monitoring signals. Developed for fast deployment in heterogeneous railway and industrial applications, the versatile BBU-S is available with AC or DC input voltage and can charge and control multiple battery pack configurations. The BBU-S starts at 340W and is available up to 1200W. For remote monitoring and control, the BBU-S offers multiple options such as LAN interface, a radio communications module (GSM, 3G, LTE) and can be reconfigured to match specific demands as

needed for different applications.

Combining a high efficiency switching topology with advanced control and monitoring, the new generation of PRBX BBU-S is the ideal solution to power railway trackside applications such as signaling, offering a significant cost and energy saving compared to conventional technology. The BBU-S includes a range of products that can be quickly modified to meet specific demands such as adaptive voltage and power to suit the length of the track, and to the number of systems installed in the signaling network.

Railway and demanding industrial applications have mandatory re-quirements that any parts installed in a critical system must have the provision to be quickly and easily repaired or replaced. Based on a range of plug-and-play modules, the PRBX BBU-S can be installed, maintained, repaired and eventu-ally decommissioned with the minimum possible downtime of service, often just minutes.“Railway modernization programs are now integrating digital control and additional safety functional-ities that require a new genera-tion of equipment for signaling,

one that includes monitoring and independent battery backup. Most, if not all modernization programs will require it necessary to main-tain and upgrade existing systems without any traffic disruption. This demands a high degree of flexibil-ity in the power solution deployed at the trackside.” said Patrick Le Fèvre, Powerbox’s Chief Marketing and Communication Officer.“ To achieve this goal, we developed the modular concept BBU-S, making it easy to adjust and adapt to differ-ent configurations. Existing power modules and monitoring units can be substituted by fitting the new generation ones into the existing chassis, and in the cases of expan-sion or high level upgrades that require a very short time to achieve operational status, the new modu-lar racks can be customized to specific configurations to power new signaling equipment such as optical fiber transmission.”

The BBU-S is built in two 3U 19 inch racks containing the power supplies, charger and control unit on the top, and battery switches, inverter block and alarm switches in the bottom rack.

Powerboxwww.prbx.com

NOTABLEandNewsworthy

6

MARKETwatch


By: Kevin Parmenter, PSD Contributor

We hear many thoughts on Industry 4.0, the Industrial IoT

(IIoT), and 3D printing regarding their impact on manufacturing. Each new innovation, regardless of of where it occurs production process or in the processing, will need power electronics to make it all happen. The industrial market has been a steady one over the years, posting continued growth while the rest of the electronics market is in flux. With all the changes brought on by Industry 4.0, what are the key trends in industrial power that can make or break an enterprise’s Industry 4.0 implementation?

First, industrial power specifications are changing. Specification 60950 is being integrated into a new specification, 62368, which is more of a risk-based approach to safety. The PSMA Safety and Compliance Committee recently hosted a presentation from UL on 62368-1, which has been archived on the PSMA website at no charge, and can be found at http://www.psma.com/technical-forums/safety/presentations. This standard, 61010, and the legacy

3 Key Trends in the Age of Industry 4.0

UL508(A) and 60950 are the most often referenced requirements for industrial power supplies. Humidity can be a concern so conformal coating of the power supply might be requested from time to time depending on the application.

The other trend in industrial power is a focus on resiliency, specifically the ability for a power supply to sustain more severe line surges and transients – 300 volts for 5 seconds with no damage and the ability to withstand line transients and spikes to the K.21 level, IEEE C62.41-1991 or equivalent is not uncommon.

A third trend is that legacy instrumentation systems, which used linear power supplies, now need to convert to switching power supplies. It was thought that the very low noise offered by linear power supplies made it impossible for switchers to be used in many of these applications. This belief has been entrenched in the engineer’s minds for so long, they did not even try to replace linears with switching power supplies in certain applications. We now see commercial linear power

supplies being discontinued, and the tap switching fuse holders to support these power supplies also being discontinued. These discontinuations are forcing conversion. The additional size, weight and heat of the linear, coupled with the inability to automatically adapt to line voltages all over the world are also key factors in converting. Using filtering techniques, careful grounding, and shielding schemes can allow switching power supplies to replace linear supplies with all the associated benefits. New fanless power supplies also offer the ability to have sealed boxes so as not to pull in contaminants in along with cooling air inside the systems as well as eliminating the noise and vibration associated with a fan. Some industrial applications, such as analysis instrumentation and measurement systems resolving nanometers, do not deal well with vibration from any source including fans. Subsequently, it is incumbent upon power providers to make power conversion more efficient so we can remove fans and seal products.

PSDwww.powersystemsdesign.com

Increasing the Power Density and Efficacy of Datacenters Using a Two-Stage Solution for 48V By: Qian Ouyang, Rohan Samsi, and Jinghai Zhou, Monolithic Power Systems

Current datacenters typically have a 12V backplane and distribution on

board and need to convert the voltage down to around 1V, which is usually achieved with a synchronous buck regulator, single- or multi-phase. The racks in these datacenters normally max out at a power rating of 20kW. There is a need in the industry to increase the power density per-rack to about 100kW to reduce the size of these datacenters. This can be achieved by using a 48V backplane and distribution, but there are challenges associated with this approach. To drive 48V down to the board, traditional synchronous buck regulators cannot be relied on. How, then, does one increase the density of datacenters without also increasing cost? This paper outlines a two-stage solution to drive 48V down to the point of load (POL, approximately 1-5V) in a flexible, scalable, and cost-effective manner that will benefit the next generation of server power delivery.

Proposal

As the demand for datacenters has increased, so has the need for increasing their size and density to accommodate the needs of all users. One of the key limiting factors is the power limitation of servers per rack, which is around 20kW. This limitation arises due to a suboptimal power distribution network. Most mid-planes and backplanes operate at 12V, which requires a large volume of copper and limits the power per rack. The Open Compute Project (OCP) and Google have proposed ideas that would increase the operating voltage to 48V, thereby increasing the installed capacity per-rack to 50-100kW per rack. One of the key reasons why this architecture has not yet found success is due to the lack of downstream solutions (i.e.: 48V down to the board-mounted POL, including processors, memory banks, and other ASICs).

There have been a few different approaches proposed to address the 48V input to POL distribution problem. The main challenges to overcome include scalability, cost, efficiency, and size.

Scalability and Cost It is difficult to distribute 48V to a variety of loads, including small currents used for rails, such as USB and VGA ports, that typically consume a few hundred milliamps each at 2-5V and scale up to the processors, which consume hundreds of amps at close to 1V. Some available solutions include driving the voltage directly from 48V to the load voltages (1-5V) by accurately regulating an intermediate bus and using a DC/DC transformer for the final step-down.

While these solutions are effective for the high-current rails, they are both hard to scale down and more expensive for the majority of the low-current rails, and can even be more expensive for high-current rails as well. Other solutions, such as the use of gallium-nitride (GaN), have been proposed to solve these issues to perform a direct conversion using a simple, synchronous, buck solution. While they do hold significant promise when cost and large volume manufacturability become viable, these solutions at present appear to be distant.

DESIGN t ips


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The first-stage modules can be scaled as a function of the power delivered, but for a typical single-processor server, only two of these modules are necessary. Another unique feature of this first stage is that it can be multi-sourced. When technologies such as GaN become more prevalent, they can replace these modules seamlessly without affecting the downstream solutions. The variable 5-8V unregulated voltage can also be replaced by a tightly regulated voltage between 5-8V without causing any disruptions to the overall system so that interoperability is maintained.

Stage 2 The second stage depends entirely on the power to be delivered. In the case of a milliamp load, the second stage could be as simple as using a linear low-dropout (LDO) regulator. As the power level increases, the second stage could utilize single-phase, synchronous, buck regulators, which are plentiful. With the reduction in input voltage, the need for low-duty ratios is reduced, and the field-effect transistors (FET) and efficiency can be optimized, reducing losses. By reducing the need for high breakdown voltage FETs as compared to the typical 12V rail, the cost of the devices is reduced, and their figure of merit is improved for efficiency. For higher current solutions for processors and

memory, interleaved multi-phase regulators can be used (see Figure 2).

With the reduction in input voltage, these multi-phase converters can achieve a peak efficiency of about 97%. With the improvements in feed forward control in most of these converters, the floating input voltage (5-8V, output of the first stage) can be handled easily. The size of these converters is made smaller by using high-frequency conversion, which uses smaller inductors and fewer capacitors.

Summary/Conclusion The overall efficiency of this solution would be about 95%, which exceeds the 93% target for 48V-to-1V conversions and matches the 12V-to-1V state-of-the-art conversion efficiency. The size of the board is not increased since the module can be mounted vertically. The subsequent gains of the size reduction of the second stage account for the increased size of the first stage. The flexibility of using any second-stage converter and correspondingly sizing the first-stage converter increases scalability. With this solution, datacenters can achieve 100kW per rack of density without increasing cost and size.

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Efficiency and Size The solutions of the board must have both high efficiency and a small size to fit on a current server board. Efficiency of the 48V-to-1V conversion must be at least 93% or above, since the state-of-the-art conversion efficiency is 95% for 12V-to-1V conversion. The size of the 48V-to-1V converters must be no larger than the 12V-to-1V converters due to the limitations of the dimensions of the industry-standard rack and the planar boards that plug into the backplane.

Solution The

proposed solution for 48V-to-low-voltage distribution is a two-stage process that will improve efficiency, scalability, and cost compared to existing datacenters.

Stage 1 The VIN rail (48V) is distributed

across the board and subsequently stepped down to a variable intermediate voltage, typically between 5-8V. The variable 5-8V can be generated in clusters for CPU and memory power, while the rest of the power distribution (totaling about 50W) can be generated from a separate converter. The intermediate floating rail ensures complete soft switching, achieving a peak efficiency of 98% by using a half-bridge, resonant, LLC converter. Isolation is not necessary since the input voltage is below 60V. Functional isolation can be achieved more easily by using a transformer in place of an inductor as part of the LLC network. This also aids the step-down from 48V to 5-8V. The fundamental idea is to modularize this first-stage solution (see Figure 1).

Figure 1: Front View of First-Stage Module

Figure 2: Second Stage

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COVER STORY



High Power Density Systems Demand High Current Converters

By: Steve Knoth, Senior Product Marketing Engineer, & Steve Zhou Senior Design Engineer, Linear Technology, Now Part of Analog Devices

High power density digital IC-based systems have a unique set of power requirements

The expanding market for high current, low voltage digital ICs reached $9.2B in

2016 [source: Intense Research Co]. This group of digital ICs includes microcontrollers and microprocessors (µC & µP), programmable logic devices (PLDs), digital signal processors (DSPs), application specific integrated circuit (ASICs), programmable logic devices (PLDs) and graphics processor units (GPUs). Furthermore, looking at the projections for a big subset of this market – Field Programmable Gate Array ICs (FPGAs) – this segment was valued at $3.92B in 2014 and is expected to reach $7.23B by 2022, with a CAGR of 7.41% between 2016 and 2022 [source: marketsandmarkets.com]. High power density digital ICs have penetrated into virtually every embedded system. These systems include, but are not limited to, industrial, communications, telecom, servers, medical, gaming, consumer audio/video and automotive. FPGAs are enabling cutting-edge applications to come to fruition within these

market segments, for example in automotive applications to remove human errors, such as advanced driver assistance systems (ADAS) and collision avoidance systems. Moreover, government–mandated safety features such as anti-lock brake systems, stability control and electronically controlled independent suspension systems have necessitated the use of FPGAs. In the consumer electronics sector, the demand for Internet of things (IoT), machine to machine (M2M) and the growth of data and server centers driven by the demands of large data storage and cloud computing are some of the factors also driving the FPGA market.

These high power density digital IC-based systems have a unique set of power requirements. The combination of high current, low voltage and fast transient response for this current generation of FPGA and ASIC processors place ever more stringent demands on the power supplies that power the device. These digital ICs are powerful, yet temperamental from a power standpoint. Traditionally,

efficient switching regulator controllers with separate high power MOSFETs have been used to power these devices but they have exhibited potential noise interference issues, slower transient response and layout limitations. As a result, in recent years low dropout regulators (LDOs) that minimize heat have been used as an alternative, but not without their own set of limitations. However, thanks to recent product innovations in this area, the trend is changing. Newer high power monolithic switching regulators no longer come with performance tradeoffs and are rapidly finding their way into these applications.

Switching Regulators vs Charge Pumps & LDOs Low voltage high current step-down conversion and regulation can be achieved via a variety of methods with a variety of design tradeoffs. For starters, switching regulator controllers operate with high efficiency for high currents over a wide range of voltages but require external components such as inductors

and capacitors (and FETs in the controller case) for operation. Inductorless charge pumps (or switched capacitor voltage converters) can also be used to achieve lower voltage conversion but are limited in output current capability, suffer from poor transient performance and require more external components versus a linear regulator. As a result, charge pumps are not commonly found in digital IC power applications. Conversely, linear regulators and especially LDOs are simple in that they only require 2 external capacitors to operate. However, they may be power limited depending on the size of the input to output voltage differential across the IC and how much current is demanded by the load, plus the thermal resistance characteristics of the package. This limits their penetration into powering digital ICs.

High Current Monolithic Buck Converter Design ChallengesClosely following Moore’s Law (originally conceived in 1965), wafer fabrication technology line widths are ever decreasing, therefore requiring lower voltage operation of digital ICs. Smaller geometry processes allow higher integration of more power-hungry features in the end product. For example, modern computer servers and communication routing systems demand higher bandwidth to process more computing data and internet traffic. Cars have more on-board electronics for

entertainment, navigation, self-driving features, and even engine control. As a result, system current consumption and associated total power required increases. Therefore state of the art packaging and innovative internal power stage design are required to drive the heat out of the power IC while delivering unprecedented power.

The requirements for high power supply rejection (PSRR) and low output voltage noise or ripple are two additional challenges which also need consideration. A device with high supply rejection can more easily filter and reject noise at the input, resulting in a clean and stable output. Further, a device with low output voltage noise across a wide bandwidth or low output ripple is beneficial to power today’s modern low-noise rails where noise sensitivity is a major design consideration. As the speed requirements for high end FPGAs increase, the supply noise tolerance continues to decrease in order to minimize bit errors. These noise-induced digital faults drastically reduce the effective data throughput speeds for these high speed PLDs. Input supply noise at high currents is clearly an important but demanding specification.

Higher transceiver speeds – in FPGAs for example - dictate higher current levels due to higher power consumption from fine geometry circuit switching. These ICs are fast – they may cycle load current

from near zero to several amps in tens to hundreds of nanoseconds, requiring a regulator with ultrafast transient response.

With board area reserved for the power regulators ever decreasing, it is well known that a monolithic switching regulator with fast switching frequency reduces the size of external components and therefore total solution size, with a tradeoff of some minor loss in efficiency due to switching losses at higher frequencies. However, a new generation of monolithic switching regulators provides unique features that significantly reduce the amount of switching losses even at higher frequencies. Namely, synchronous operation with integrated high and low side switches allows for better control of their gate voltages which greatly reduces dead-time thereby resulting in higher efficiency operation.

One of the biggest challenges with high current monolithic switchers is their ability to dissipate heat resulting from significant power loss in the IC. This challenge is met by using thermally enhanced ball-grid array (BGA) packages where the majority of the solder balls are dedicated for power pins (VIN, SW, GND), such that the heat can be easily transferred from the IC into the board. The large copper planes on the board connecting to these power pins allows for the heat to spread more evenly.

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COVER STORY



New High Current Buck ConvertersIt is clear that a buck converter solution which solves the issues outlined herein needs to have the following attributes:• Fast switching frequency

– reduces size of external components

• Zero dead-time design - for increased efficiency

• Monolithic – onboard power devices for smaller solution size

• Synchronous operation – higher efficiency and reduced power loss

• Simple design - minimal external components required

• Very low output ripple• Fast transient response time• Operation over a wide input/

output voltage range • High output current capability• Excellent thermal performance• Compact footprint

To address these specific needs, Linear Technology introduced the LTC71xx family of monolithic high current buck regulators. The newest member is the LTC7150S, a 20V / 20A monolithic synchronous buck converter with differential VOUT remote sensing. The device’s unique phase lockable controlled on-time constant frequency current mode architecture eases compensation and is ideal for high step-down ratio applications that operate at high frequencies while demanding fast transient response. The LTC7150S uses Silent Switcher® 2 technology, including integrated

bypass capacitors to deliver a highly efficient solution at high frequencies with excellent EMI performance. Multiphase operation - up to 12 phases - provides the capability to directly parallel multiple devices for higher current with minimal input and output capacitance. VOUT remote sense ensures that voltage regulation at the load is accurate regardless of load current or board layout. Its wide 3.1V to 20V input range supports a wide variety of applications, including most intermediate bus voltages and is compatible with many battery types. Integrated N-channel MOSFETs deliver continuous load currents as high as 20A with minimal thermal derating at output voltages spanning from 0.6V to VIN, ideal for point-of-load applications such as high current/low-voltage DSP/FPGA/ASIC reference designs. Other applications include telecom/datacom systems, distributed power architectures and general high power density systems. Figure 1 shows a typical

application schematic exhibiting the simplicity of the design.

The LTC7150S’s very low 25ns minimum on time allows for a high step-down ratio power supply at high frequency operation. The operating frequency is user-selectable from 400kHz to 3MHz and can be synchronized to an external clock. The LTC7150S’s total differential output voltage accuracy is ±1% over the –40°C to 125°C operating junction temperature range. Additional features include a high speed differential remote sense amplifier, PHMODE phase selector pin, accurate 1.2V RUN pin threshold, VIN overvoltage protection, Power Good and programmable soft-start/tracking.

Lastly, the LTC7150S is available in a thermally enhanced 42-lead 6mm × 5mm × 1.3mm BGA package, both RoHS lead-free and leaded SnPb (63/37) finishes. The E and I grades are specified from –40°C to 125°C junction operating.

High Efficiency, Reduced EMI &

Fast Transient ResponseThe “S” in the LTC7150S part number refers to the second generation Silent Switcher technology. The IC has integrated ceramic capacitors for VIN and BOOST to keep all the fast AC current loops small, thus improving the EMI performance. Furthermore, it allows for faster switching edges, which greatly improves efficiency at high switching frequencies.

The LTC7150S’s unique controlled on-time architecture allows the IC to respond to transient steps rapidly. This is accomplished during the transient step - the switching frequency inherently speeds up which allows the inductor current to better shadow what the output of the Error Amplifier (ITH) wants it to be. This allows the ITH compensation to be set more aggressively, increasing overall loop bandwidth.

One key feature of the LTC7150S

that allows for high efficiency at high frequen-cies is the signif-icant reduction of dead time. A servo loop inside the IC locks the dead-time before the SW rising edge to <1ns. The reduced dead time minimiz-

es/eliminates the need for body diode con-duction of the bottom switch. This essentially eliminates the effect of the reverse recovery of the bottom switch body diode as top switch turns on. The reduction in power loss with this feature is quite signifi-cant.

Lower ripple current reduces core losses in the inductor, ESR losses in the output capacitors and output voltage ripple. High efficiency opera-

tion is obtained at low frequency with small ripple current. However, achieving this requires a large in-ductor. There is a trade-off between component size, efficiency and operating frequency. The graph in Figure 2 shows the LTC7150S’s high efficiency performance.

The unique constant frequency/controlled on-time architecture is ideal for high step-down ratio applications that operate at high frequencies while demanding Figure 1: LTC7150S Typical Application Schematic (7150 TA01a)

Figure 2: LTC7150S Efficiency Performance (7150 TA01b)

Figure 3a (top) & 3b (bottom): LTC7150S Transient Response Performance

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COVER STORY


fast transient response. Figure 3 shows the LTC7150S’s transient response performance.

Ultralow DCR Current Sensing ApplicationsThe LTC7130 is a constant fre-quency peak current mode con-trol synchronous step-down DC/DC converter with temperature-compensated ultralow DCR cur-rent sensing and clock synchro-nization. The device’s unique architecture eases compensation and offers the ability to directly parallel it for higher output cur-rent capability. It also enhances the signal-to-noise ratio of the current sense signal, enabling the use of a very low DC resis-tance power inductor to maxi-mize efficiency in high current applications. This feature also reduces the switching jitter com-monly found in low DCR applica-tions and improves current limit accuracy. The LTC7130’s 4.5V to 20V input range supports a wide variety of applications, including most intermediate bus voltages, and is compatible with many bat-

tery types. Integrated N-channel MOSFETs can deliver continuous load currents as high as 20A at output voltages ranging from 0.6V to 5.5V, making it ideal for point-of-load applications such as high current / low-voltage DSP/FPGA/ASIC reference de-signs. Other applications include telecom/datacom systems, distributed power architectures and general high power density systems. Figure 4 shows a typical application circuit.

ConclusionThe continuing trend in high-

performance digital ICs such as FPGAs and µPs are ever increas-ing current with corresponding lower operating voltages, enabled via shrinking line width wafer fabrication technology. Neverthe-less these advancements come with other application demands; in the power management arena these include the need for fast transient response, low noise/ripple, and efficient operation to minimize heat. Traditionally, pow-

Figure 4: LTC7130 Typical Application Circuit (7130 TA01a)

Table 1: Comparison of Key Specs of the LTC7150S & LTC7130ering these digital ICs has been performed by LDOs or inductor-based switching regulator control-lers with off-board power devices; however, a new generation of monolithic, high current switch-ing buck regulators in thermally-efficient BGA packages is offered from Linear Technology to solve these problems. These products include the LTC7150S and LTC7130, both having a unique feature set to address a wide variety of applica-tions for powering digital ICs.

Linear Technologywww.linear.com

Changing Demands for the Power Industry

By: Patrick Le Fèvre, Chief Marketing and Communications Officer, Powerbox

Will the Power Supply Industry Adopt the Cradle-to-Cradle Business Model?

Due to its very nature, the power supply industry has been on a never-ending quest

searching for new technologies to improve energy efficiency, safety and miniaturization. Step by step - sometimes small ones, sometimes big – the industry has created power architectures that reduce energy consumption and in many cases has discovered technical solutions to supposedly ‘unsolvable’ problems. Those achievements are great but are they enough to address the growing demand from the market to reduce - even further - the environmental impact?

Risks under controlTechnology has helped us to perform ‘magic’ but at the same time the world has changed and environmental challenges have become more complex and global, requiring all industries to reconsider their ways of working, particularly with a higher regard and responsibility for environmental and social issues.

This is the latest challenge that the power industry is now facing, and

despite the fact that the technologies brought to the market have helped reduce CO2 emissions, companies’ Corporate and Social Responsibility (CSR) policies aligned to international standards will require many adjustments in the way they are working. Not only that, but the issue of how their suppliers will comply with such environmental regulations and manage the related risks.

One example is the implementation of the global risk management ISO 31000 methodology. This was initially developed for decision and policy makers within governments and large corporations in order to minimize exposure to risk and to secure business integrity for stockholders, and is now adopted by many companies such as those in the medical industry.

ISO 31000 is becoming an important tool, helping companies to develop their environmental strategy and gain better control

of risk, both internal and external. ISO 31000 is defined as ‘a process that provides confidence that planned objectives will be achieved within an acceptable degree of residual risk’. Moving forwards, ISO 31000 will become an immense and increasingly important part of organizations.Clearly, many power supply designers are used to dealing with risk management assessment (e.g. when designing a medical power supply to comply with the IEC 60601-1-3 Edition, or a power supply for demanding applications in other segments such as in gas and oil industry), though in coming years the demand from OEM customers on the power

Figure 1: Medical power supply OFM225 used as pilot case for C2C simulation

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manufacturing, sales, logistics, installation, commissioning, deployment, and end of life management.

The fundamental principle of the IEC 60601-1-9 is to protect the environment and human health from hazardous substances, to preserve raw materials and energy, minimize the generation of waste, and minimize the adverse environmental impact associated with waste.

Without going into microscopic detail, the core requirements of IEC 60601-1-9 can be summarized as ‘identification’, ‘instruction’, and ‘end-of-life management’. During this process, manufacturers will have to perform in accordance with existing processes (e.g. risk management performed in compliance with ISO 1497, life-cycle thinking, in line with ISO 14001 with particular emphasis on ISO 14062) and develop documentation demonstrating

that all steps have been carried out with the highest consideration for the environment.

Since IEC 60601-1-9 was amended in 2013, the standard has been used to guide and help companies minimize products’ and operational environmental impact and has been implemented on a voluntary basis. However in 2014 the Brazil National Health Surveillance Agency (ANVISA) took the lead, requiring that any medical electrical equipment sold into the country meets the standard by December 1, 2016 with special attention to three clauses: (4.1) Identification of Environmental Aspects, (4.5.2) Instructions for Minimizing Environmental Impact During Normal Use, and (4.5.3) Information for End of Life Management.

Brazil is the first country to stipulate that medical electrical equipment formally complies with the standard, but other

countries are also considering its implementation or national directives aimed at motivating medical equipment manufacturers to include parts of the standard to minimize impacts, and contribute to the development of a sustainable economy that preserves the environment.

Could the power industry adopt the cradle-to-cradle business model?As engineers we enjoy challenges, solving problems, and to some extent we are used to breaking ‘unbreakable’ limits. The power supply history is awash with examples of ‘that which will never be possible’ eventually becoming a ‘great innovation’. In terms of contributing to the environment, by permanently improving technical performance and reducing energy consumption, we have proven our ability to contribute to the reduction of environmental impact, but we can do more. Integrating the full life cycle stages and complying with standards such as ISO 60601-1-9 (or equivalent) are good, but looking forward can we rethink the way the power supply industry is working? Can we contribute even more to build a sustainable environment for future generations?

As part of an internal project, a group of engineers from different disciplines and companies were invited to project the complete life cycle of Powerbox’s OFM225 power supply (Figure 1). The

Figure 3: Cradle-to-Cradle Quality categories addressed for certification

supply industry in term of risk management might become more global, including environmental impact and social responsibility down to a single supplier. That requires our industry to be prepared for new ways of working and even to consider revamping some of the business principles that we thought were engraved in stone. Are we ready for that?

Medical drives trends!Addressing a vast range of applications, from consumer to defense, the power supply industry has to comply with many standards and regulations. Some of these, originally developed for a specific segment are now rapidly being adopted by other industries. Regulation in the medical industry is a good example where a number of parameters specified in the IEC 60601-1-3 and -4 have now been adopted by industrial project managers involved in ‘Industry 4.0’ (e.g. higher isolation, lower leakage current, reduced and in-

control EMI and documented risk assessment).

Designing power supplies and complying with safety regulations is for sure a vital obligation, but designing a product for the environment (DfE) is just as important. Here again, the medical industry is setting the scene and according to a market study released in 2014 by Johnson & Johnson, more than 80 percent of the hospitals around the world are expected to incorporate sustainability into their purchasing decisions and for many to follow ISO 31000’s risk assessment process - including their suppliers.

That considered, one way or another the power supply industry will have to comply with environmental requirements demanded by the medical industry, and by other industries formulating the same demands on their suppliers and partners. Therefore it becomes very important for the

power supply industry to adopt a way of working that includes environmental aspects at the very early stages of any project.

Designing for the environment has often been performed on a voluntary basis or used as a marketing/sales argument, though that is now changing. For many, a product with high efficiency and low standby power may seem to be DfE by nature, but that is not necessarily the case. DfE is much more than that and despite the existence of ISO 14062, the lack of a common definition or standard that is relevant to the electronics industry is making it difficult for customers and users to verify what is included under each company DfE definition and verification.

Being aware of the difficulties in assessing the different variables considered as part of DfE from their suppliers, the medical industry and regulatory bodies realized the need to define a standardized methodology that considers the overall life cycle.

Following several years preparation, in 2007 as collateral to the IEC 60601 the International Electrotechnical Commission (IEC) published the so-called ‘dash one nine’; IEC 60601-1-9. The objective of IEC 60601-1-9 is to reduce the environmental impact of the entire range of medical electrical equipment (ME equipment), taking into account all stages of the product life cycle, namely product specification, design,

Figure 2: Cradle-to-Cradle three phases methodology for continuous improvements strategy

power supply had originally been designed for high efficiency and ease of manufacturing, and the group was asked to explore how, outside the established business model, could such a product/process not only have the lowest possible environmental impact, but also be able to optimize the positive impact (e.g. Supporting local economy).

Taking into consideration all aspects from initial design to end-of-life (and potential second life), the project followed the cradle-to-cradle (C2C) approach and identified areas to work on in order to minimize negative impacts and optimize positive ones (Figure 2).

For many it may seem an odd approach for a power supply company to consider revamping a conventional way of working to adopt such a model, but considering that C2C takes the whole lifecycle of an item into account, including sourcing and end-of-life disposal, it becomes synchronous with existing and forthcoming regulations, with customers, end-users and stakeholders expectations, and a way forward for the power supply industry to help create a better world.

Integrating the C2C five goals (Figure 3) at the beginning of a project will contribute to the development of power supplies

with the lowest environmental impact while increasing the positive ones (e.g. selecting a components supplier engaged in sustainable development, working with CEM partners to reduce water consumption and to use renewable energies, designing products with end-of-life or second life in mind), contributing to make the power supply industry, not only able to provide products with best in class technology, but to contribute to local economies and the development of a new way of working, paving the way for future generations.

Powerboxwww.prbx.com

www.taiyo-yuden.com

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Implementing Tapped Buck Topology

By: Silvestro Fimiani, Product Marketing Manager, Power Integrations

Tapped Buck AC-DC Power Topology Optimises Cost in ErP-Restricted Appliance PSU Designs

When designing a medium power (10 W – 20 W), non-isolated, AC-

DC power supply the choice is typi-cally between a conventional buck topology and a more complex, flyback transformer based circuit. The buck converter design, al-though simple and easy to design with, has some drawbacks. Buck converters use a simple low cost inductor for the energy storage ele-ment but require a large expensive power MOSFET, especially if the output current is in excess of 400 – 500 mA, and a high voltage (600 V) high current, fast freewheeling diode. The fly-back design uses a more complex transformer in place of the inductor and re-quires a smaller power MOSFET and lower voltage (and therefore

lower cost) free-wheeling diode. Flybacks can also provide output isolation if required.

In terms of which is most efficient – buck or flyback - that mostly de-pends on the input vs output volt-age and current requirements. If there is a large difference between the input and the output voltage, then the flyback topology is likely to be more efficient because the turns-ratio naturally steps the voltage down, whereas the buck

needs a reduced duty cycle which increases the peak currents and I2R losses. If the ratio is small, then the buck topology is likely to be better because flybacks need a primary clamp in the flyback circuit and also there are magnetization and leakage inductance losses in the flyback’s transformer core.

There is a third AC-DC converter architecture which offers reduced cost compared to the conventional buck converter design and re-

Figure 1: Tapped Buck Schematic

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part completes a normal start-up sequence. Hysteretic thermal shutdown includes automatic recovery that allows the controller to restart once the IC temperature has reduced to below 85 deg C. During normal operation, the by-pass (BP) pin is powered from the main output of the circuit through

D3 and R3. Quiescent (no load) power consumption can be opti-mised by careful selection of R3 and C3. The leakage energy in T1 causes drain voltage spikes which are typically limited to below 90 % of the breakdown voltage rating of the internal power MOSFET. To minimise the leading-edge spikes, a snubber circuit consisting of an

Figure 3: Efficiency vs Load at room temperature measured at the Output Terminal.

Figure 4: Output voltage ripple vs output load

RCD network comprising made D2, C4, R4 and R5 is used to limit the voltage excursions and reduce stress switching element. Output ripple is controlled by the output smoothing capacitor C5. To keep the ripple below 200 mV the out-put capacitor needs to have low ESR. The tapped buck design illustrated in Figure 1 is based upon the Power Integrations Design Example Report DER-572 for a 10 W (12 V – 20 V, 500 mA output) AC-DC power supply. Designers using the methodology described in the report can expect to see efficiency greater than 82% from half-load to full-load, and 72 % at 10 % load for a 115 V AC supply (which drops to 67 % for a 240 V AC supply). This performance is described in Figure 3.

Output ripple is maintained at less than 182 mV across the load range and across the line input voltage range (85 – 265 V AC). Voltage ripple is shown in Figure 4.

DER-572, is freely available to download from the Power Inte-grations web site and contains all design and layout information as well as detailed instructions on how to wind the Tapped Buck transformer. Details of the full LinkSwitch family can be found on Power Integrations website.

Power Intergrationswww.power.com

duced complexity compared to the flyback design, the tapped buck. Tapped buck PSUs have the benefit of a turns ratio to assist with large voltage conversion ratios and are generally more efficient than non-isolated flyback designs; up to 2% in some cases.

The tapped buck topology uses a simplified transformer which operates as an auto-transformer, where the primary and secondary are directly connected. The trans-former reduces the output voltage but maintains the same current flowing through both windings. This reduces complexity, weight and cost of the transformer but does not provide the output isola-tion that is typically provided in a conventional flyback design. An additional feedback winding is added which ‘taps-off’ a propor-tion of the input voltage (similar to the secondary tap) to feed back a control voltage to the switcher. The tapped buck architecture utilizes the smaller, lower cost MOSFET and lower voltage freewheeling diode seen in flybacks. The tapped buck architecture also has the advantage of producing less stress on the switching MOSFET during commutation improving long term reliability.

Figure 1 illustrates the schematic for an 85 VAC – 240 VAC input, 20 V 500 mA (10 W) output AC-DC converter using a tapped buck topology. This design uses Power Integations’ LinkSwitch-CV IC (LNK626DG), U1, configured as a high side driver. The schematic

looks very similar to a conventional inductor-based design except that the inductor is split into primary and secondary windings, linked at a common point which is then connected to the free-wheeling diode D1. When the power MOS-FET in LNK-626DG switches on, the current ramps up through the transformer T1, storing energy, which flows out through the load - as is the case with a conventional buck converter. When the power MOSFET switch-es off, the magnetic field starts to collapse causing a reversal of the voltage across the inductor, and the stored energy is converted into a current which flows out via the load, returning via the free-wheeling diode. The peak current is stepped-up by the turns ratio be-tween the primary and secondary windings. The feedback winding provides a control voltage which is connected to the feedback (FB) pin via a potential divider formed by R2 and R1. The feedback voltage is set by the feedback winding turns ratio and the potential divider ratio to provide the required 20 V out-put voltage.

The LinkSwitch-CV family inte-grates a wide range of protection features which make the LNK-626OG ideal for energy efficient

EcoSmart off-line switching power supplies. LNK626DG can oper-ate in continuous or discontinu-ous mode and compensates for external component temperature variations. ON/OFF control pro-vides constant efficiency over a wide range of loads and retains this high efficiency at light loads, making LinkSwitch-CV perfect for applications that need to meet ErP regulations. No-load power dissipation can be reduced to less than 70 mW by switching to a conventional flyback design with the addition of an external bias circuit as depicted in Figure 2.

Advanced protection features include auto-restart in the event of output short circuit or control loop faults. During auto-restart, the power MOSFET is disabled for 2.5 seconds then switched on for 200 mS (8 % duty cycle). If the fault is no longer present, the

Figure 2: External bias for reduced quiescent power consumption

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Resistor Specifications And How To Interpret Them

By: Kory Schroeder, Director of Marketing & Product Engineering, Stackpole Electronics

Consider different performance characteristics that might be confusing

Resistors are one of the simplest electronic components. However, the specifications

typically shown on datasheets can be confusing, and are often misinterpreted. In this article we discuss the different performance characteristics, the test conditions, and how to interpret the test results. We discuss potential differences in data presented by different manufacturers and what those differences will mean in terms of performance.

Resistor Power Ratings and Voltage RatingsThe power rating and voltage rating of a resistor are one common source of confusion. Simply put, the power rating is the amount of energy the resistor can dissipate in a given time at the designated ambient temperature.

Multiple voltage ratings are typically provided on a datasheet, but most often the primary concern is the maximum working voltage. Maximum working voltage is the maximum amount of voltage the resistor

can withstand constantly without arcing. Maximum working voltage is often expressed as “Vrms.”

It is critical to adhere to both the power rating and the maximum working voltage rating to avoid reliability problems. For example, if a 10Ω 0603 chip resistor was subjected to the maximum working voltage of 75 volts, the resulting power through the part would be 562.5 watts. This far exceeds the power rating of the part.

Conversely, for high resistance values, the amount of electrical energy that the 0603 resistor can withstand is determined by the working voltage rating

of 75 volts. If a 10MΩ 0603 was subjected to the maximum power of 0.1W, the voltage implied across the part would be 1000 volts, which surpasses the voltage handling of the part.

As shown in Figure 1 above, it is clear that only at exactly 56.25K ohms can the 0603 resistor handle both 75 volts and 0.1W simultaneously. This value is known as the “critical resistance value”.

Another aspect of the power rating is the temperature at which heat dissipation is measured. Many resistors are rated at temperatures of at least 70C. This means the part can handle the designated power

Figure 1: Power / Voltage vs. Resistance Value

rating provided the ambient temperature around the part does not exceed 70C. However, there are some higher power resistors that are only rated for full power operation up to 25C. These power resistors typically require some type of external heat removal to operate at full rated power.

As can be seen from the derating curve in Figure 2 above, if the part associated with this derating curve is to be used at 70C, the power rating must be reduced to roughly 65% of its full value. Operating this part at full power and elevated temperature will lead to excessive resistance shifts and potentially failure of the resistor.

Performance Characteristic InformationPerformance characteristics provide information about how a resistor performs in a test or a set of tests. Engineers will

regularly use this information to compare and contrast parts from different manufacturers. When resistor series are tested to a common standard such as AEC-Q200, it is relatively easy to compare performance.

When common test standards are not followed, both test conditions and the way in which test results are stated, can vary widely. These variations can lead to misleading performance statements. For example, nichrome based thin film resistors are susceptible to moisture corrosion. Some manufacturers will tout their nichrome elements as having superior moisture resistance, citing extremely low resistance shifts to biased humidity testing.

When examining those test conditions, the load or bias on the resistor is a critical factor. At full rated power, most resistors will generate enough heat that

moisture will not condense on the part, making it appear robust in terms of moisture. But in many applications, precision nichrome thin film resistors will only see a fraction of the rated power. In these cases, the part will generate much less heat and the possibility of moisture condensing and collecting on the part increases. The resistance shift could be significantly different under a lower bias condition, such as 10% rated power. The test conditions is critical to understanding the results and ultimately resistor performance.

Another frequently asked question about performance characteristics is how to interpret the accumulated variation or tolerance stack-ups from the different potential sources of variation. Adding the maximum potential shift from all of the relevant tests provides the maximum expected resistance shift or worst-case scenario.

In practice, this is unnecessarily conservative for most applications and may result in the selection of a more expensive resistor with a tighter tolerance or lower TCR. It is important to remember that each performance characteristic test is independent. Some of these tests will typically have a positive shift in resistance and some will typically have a negative shift in resistance. In addition, the typical test

Figure 2: The Derating Curve

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performance will differ from one resistor technology to the next. In most cases, the actual resistance shift experienced in the circuit or application is a fraction of the sum of the individual test tolerances. It is advisable to contact the factory about specific stability requirements over the life of a given circuit or application for a particular resistor or series of resistors.

It is also important to understand if the change in resistance shown in the performance characteristics is typical performance, or absolute maximum limits. Some manufacturers will show typical results and not state it explicitly unless they are asked specifically by the customer. Typical results are usually 2 to 3 times better than the actual test specification. This creates the false impression that their part is superior to other similar products when the actual

performance is no better and in some cases inferior.

SummaryEffective electronic designs can be achieved when critical specifications are taken into account. When selecting resistors, the design must not violate the power rating or the voltage rating of a given device; these are resistance dependent parameters. Power ratings must be reconciled with the appropriate operating temperature. If the circuit operates at temperatures above the rated temperature of the resistor, then the power handling of the resistor must be derated appropriately.

Performance characteristic testing must be closely examined to determine what tests are relevant to the application. Test specifications must be reviewed to ensure the test conditions are the same, and test results must be properly interpreted.

Test results must be verified as actual maximum possible shifts or typical performance to ensure a balanced comparison. Only then should a decision by made on the actual performance of each resistor.

Finally, when considering tolerance stackups, the accumulated variance or worst-case scenario does not consider the distribution of the individual, independent variables. This can lead to an unnecessarily constraining design and would make typical commodity resistors impractical to use. Whenever there is a question about whether a resistor is suitable for a particular design, it is recommended to have factory engineers examine the design in detail to ensure the correct product is chosen.

Stackpole Electronicswww.seielect.com

Figure 3: Example of Performance Characteristics

Benefits of digital controlled programmable AC power sources

By: Herman van Eijkelenburg, Director of Marketing, Pacific Power

With the advent of digital PWM control technology, higher efficiencies and smaller packaging of power electronics has become feasible

Programmable AC and DC power sources have been widely used to implement and support

a wide range of development and test applications where an engineer needs the ability to fully control voltage, frequency and current to the unit under test. These programmable sources are used to simulate various power conditions and anomalies that are likely to occur in actual use of AC and DC powered products. They are also essential for providing the requisite 400Hz or 360Hz to 800Hz frequency AC power to military and avionics subsystems.

With the advent of digital PWM control technology, higher efficiencies and smaller packaging of power electronics has become feasible. This has resulted in new programmable power source designs that are not only smaller and lighter than their predecessors, but also offer a number of unique features and functions made possible by this new digital domain control architecture. This article explores some new features and functions and their significance to those

developing and testing new power designs of their own.

Conventional AC Source Topologies and DesignThe vast majority of available AC power source designs are based on pulse-width modulated

control circuits and the use of low frequency transformers to provide isolation between input and output of the AC power source.

Digital Power ConversionThe higher PWM switching speeds required to support the wide

Figure 2-1: Basic Conventional (Analog) Power Source Topology

Figure 3-1: All Digital Power Source Topology

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protecting the load from any damage.

2. The output voltage is reduced to maintain the load current at or below the protection limit current value. (Constant Cur-rent mode)

The mode, CV or CC, is set by the user. In the latter mode (CC), the power source acts like a pseudo current source by regulation the current indirectly through the out-put voltage setting.

1.2 Power LimitingCurrent protection mode, as described above, works well when the equipment under test has a fairly narrow AC input voltage operating range, for example 115V ± 10%. Many of today’s AC pow-ered products use a universal, wide input voltage range of 85V to 240V. When developing or testing this type of universal input power stage, a current limit function will not be as useful. For the EUT to be tested over its entire voltage input range, the current limit must be set high enough to support max. input power at the lowest input voltage (e.g. 85V – 10% = 76.5Vin). If anything goes wrong in the power stage when operating at higher input voltages, this current limit would allow almost 3½ times the nominal power to be drawn for the AC power source (265/76.5 = 3.46 x). Such an excessive power overload can easily damage or destroy the EUT.

For these types of universal input voltage range power stages, it is

critical that the power source has a program-mable power protection mode as well as a CC or CV current mode. Power protection allows the max. VA or True Power (or both ) to be specified. This protec-tion limit will engage regardless of the voltage or current oper-ating levels.

The graph be-low illustrates the effect of adjust one or both power level limits on the output Volt-age and current profile of the AC source.

1.3 Peak current limitingWhile RMS current limiting pro-tects against excessive current flow, it is too slow to react to cata-strophic events that can occur in a design, especially during its early design stages. The AFX Series offers a unique programmable peak current function that allows the user to control what maximum peak current level is acceptable. This protection mode operates

on a switching-cycle by switching-cycle basis and responds in micro-seconds. It clamps the peak cur-rent to the pre-set limit potentially preventing serious damage to a prototype. Since early prototypes are often limited in numbers, this can avoid setting back engineering development schedules by days or weeks.

This protection mode is illustrated in Figure 4-2. As the current wave-form peaks exceed the user de-fined threshold, the output inverter power devices are turn off to keep

Figure 5-1: Single, constant power voltage range

Figure 5-2: Extended available useable range shown in green

output frequency range of an AC source, often higher than 30 kHz have made it difficult to use digital signal processors to provide all control functions. With the recent advances in DSP technologies, a full digital implementation of an AC power source design, supporting these switching frequencies, is now feasible.

A good example of this is the new Pacific Power AFX series which uses a three stage, all digital power converter design that eliminates both AC input and output transformers and allows a power density five times higher than similar contemporary products and a fourfold reduction in weight.

The block diagram below should the top level topology of this three stage converter design. The three inverters have direct coupled outputs and are capable of supporting any combination of AC and DC voltage up to the limit of the voltage range.

All power stages are synchronized internally so frequency and phase angles are precisely controllable.

Important EUT Protection FunctionsProgrammable power sources provide the design or test engineer with a wide range of capabilities and functions for design verification and performance testing.

Some of the capabilities are critical, in particular protection of

the equipment under test against excessive current, power or voltage that could result in permanent damage of the EUT. During prototype development, the loss of a prototype can result in serious schedule delays and thus cost. Some of these protection mechanisms, like programmable RMS current limit, are common in programmable power sources but others are quite new.

1.1 RMS and DC Current limitingThis is the most common protection mechanism available on AC sources and DC power supplies alike. Load current is monitored continuously and any current level that exceeds a preset user determined max. RMS or DC current level results in one of the actions listed below:1. The output is turned off

(Constant Voltage Trip mode)

Figure 4-1: Programmable Power Limit

Figure 4-2: Peak Current Limiting Engaged

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anywhere in world if needed. Of course, in the case of a program-mable AC power source, security measures are critical as unau-thorized access or access while others are working with or near the equipment can be potentially dangerous. Always check on the availability of security measures on LAN accessible power supplies or source with higher voltage output capability.

1.6 Touch Screen InterfaceAdding an external large touch screen monitors is another ex-ample of user interfacing that goes beyond regular test equipment. This allows front panel control or monitoring test data from across a lab or production floor.

Green PowerAs test equipment is often left on 24/7, energy savings features can save valuable resources as well as

Figure 6-2: LAN Access Control Browser screen

Figure 6-3: External Touch Screen Control

extend the life of the equipment itself. This is especially important for higher power models that can consume 100’s of Watts by just being turned on, even when not in actual use.

Modern designs like the AFX Series offer several energy sav-ings modes that cause the unit to turn off its output inverters while remaining in standby mode so output power can be applied almost immediately if needed. A second level can be selected which completely powers down of three power stages and place the unit is a sleep mode consuming almost no power at all.

Not only does this save energy, expected life span of the power source is increased as all switch-ing stages are dormant during this time. An additional bonus is whis-per quiet operation during periods the output is off.

ConclusionThere are many factors that affect the suitability of a programmable AC or DC power source to an end-user’s application. Understanding the various functions and capabili-ties is important when making a selection. The more information you can share with the test equip-ment vendor, the better they will be able to steer you in the best direc-tion to help you maximize your return on investment.

Pacific Power Sourcewww.pacificpower.com

the peak current from rising fur-ther.

Constant Power Wide Output Voltage RangeWhile most AC power sources have dual voltage range to allow more current to be delivered at lower voltage, this is not always practical when dealing with wide input voltage range designs men-tioned earlier. Switching between a high and low voltage range in-variably requires that the output is turned off briefly to reconfigure the AC power source’s output configu-ration. This results in momentary power loss to the EUT which often will need to be re-booted.

Such problems can be avoided by using a direct coupled, single amplifier per phase design with a constant power mode 300V rms single range output, all switch-ing and reconfiguration has been eliminated. The AFX uses this approach. The resulting available current as a function of output voltage is shown in Figure 5-1.

The additional operating areas are clearly visible if we overlay the V-I profile of a conventional dual volt-age range AC source with that of the AFX Series as is done in Figure 5-2. The additional operating area allows for full power operation over the widest possible voltage range.

User InterfaceHaving an intuitive user interface on any piece of test equipment is helpful for the user. Good exam-

ples of this are front panel touch-screen color LCD displays with simple menu operation and func-tion or soft keys, all standard on the AFX. But on the latest designs, additional ways to interact with your test equipment are available as well.

1.4 Browser InterfaceWith the growing popularity of LAN interfaces and in particular LXI compliance for test equipment, new ways to access test equipment are available to the end-user now. An LXI compliant product will have

a built in web interface allowing any browser to be used to monitor and control operation. The AFX expands on this with several ad-ditional browser pages for loading and displaying custom waveforms, setting up complex transient sequences and logging measure-ment data. No special software or instrument drivers are required for these capabilities as the web server is embedded in the product.

1.5 LAN Access Control is keyThis LAN access allows the user to access his instruments from

Figure 6-1: Program Control + Measurements and Transients Browser Screens

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Information to Power Your Designs

Power Protection Starts with Switches

By: Mike Bolduc, Global Marketing Manager, Industrial & Medical Segments, C&K

Two critical requirements for any individual piece of electrical equipment or overall power system are safe operation

Electricity is the crux of modern society. Without it we couldn't power our factories, charge

our gadgets, keep our medical equipment running or even keep food from spoiling. From lighting, communication, heating, cooling, motor control, and more, the fact of the matter is our world runs on electricity.

While the breadth of the United States’ massive electric grid is impressive, its aging infrastructure requires extensive upgrades to meet the nation’s growing energy demands. In fact, the U.S. Department of Energy (DOE) recently invested nearly $4.5 billion to modernize and enhance the reliability of the nation’s electrical framework. The funding has been used to deploy a wide range of advanced devices, including more than 10,000 automated capacitors, over 7,000 automated feeder switches and approximately 15.5 million smart meters as part of the Recovery Act, according to smartgrid.gov.

It’s clear that the stakes are high when it comes to maintaining the

high output of power and electricity in the U.S. and globally. However, with such a vast network of users, applications, and operating conditions, failures can occur almost anywhere – from the factory floor to the power generators on a cruise ship. Trouble can start from an equipment failure, physical damage, human error, or even environmental factors, and the results can be as minor as a power outage or as deadly as an electrical fire or explosion. While it’s unlikely that electric failures can be completely eliminated, there are some ways to help prevent them, such as monitoring the equipment and systems, adding protection devices, and regular maintenance. However, the best way to avoid problems is to start at the design phase, through the strategic selection of reliable components and switches that power today’s electrical equipment.

Why Power Protection MattersTwo critical requirements for any individual piece of electrical equipment or overall power system are safe operation under many diverse conditions, and the ability to energize and de-energize the

equipment being used. Electrical motors, generators, transformers, and switchgear require various amounts of electrical power to operate properly. These components can be impacted by changes in electrical power supplied to the equipment, such as under/over voltage, loss of phase, or by downstream faults, like short circuits or overload conditions. This can be caused by variations in the nature of work being performed by the equipment, damage to wiring or electrical components, and other factors.

CIRCUIT PROTECTION


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CIRCUIT PROTECTION



shedding logic which enables them to manage different loads within the facility. Air circuit breakers are also used to de-energize power to equipment when maintenance needs to be performed. Similar to MCCBs, these devices also use rotary switches to adjust trip settings and internal snap acting switches to monitor trip status.

Switch Selection for Power Protection Devices To keep the aforementioned power systems working safely and efficiently, selecting the appropriate switches is vital to their success. Because they need to last a long time, like the electrical infrastructure of buildings and factories, a long life-cycle and durability are two

big considerations for design engineers when creating power protection products.

DIP and snap acting switches are two components commonly found on most power protection devices. Both standard and rotary style DIP switches are

used on trip adjustment units to adjust current, ground fault, and time settings on both molded case and air circuit breakers. Rotary switches are also commonly used on motor overload relays to adjust the trip current. Internal snap acting switches are also used on many molded case and air circuit breakers to monitor and communicate the status of various features of the breaker such as whether the contacts are open or closed.

C&K’s RTE series coded rotary DIP switch is a common choice for trip control units on circuit breakers as well as for trip current adjustment on protection relays. It can withstand aging tests of 3000 hours at 150°C, or the equivalent of 20-years of

use. The RTE Series switches have a small footprint, are available with four, ten, or sixteen positions and feature a variety of coding options and actuator styles to increase versatility and flexibility in the design

of the end product.

Part of the DIP switch family, C&K’s SDA Series switches, are another option for adjusting the trip parameters on MCCBs. This low-profile switch comes in either a surface mount or through hole package and offers from one to twelve positions. The SDA series was designed with a contact system to resist corrosion and work reliably even under harsh environmental conditions.

When snap acting switches are needed to monitor trip status in molded case or air circuit breakers, C&K’s TF Series is an optimal choice. Current ratings from low level up to 21 amps give designers flexibility to choose a switch which meets the exact power needs of their application. The switch is also rated to perform reliably for hundreds of thousands of cycles under harsh conditions. For reduced assembly time and ease of maintenance, C&K can also design this switch into a custom module which can easily snap into the circuit breaker housing.

Power protection is crucial to keeping our electrically-powered lives running smoothly and safely, and the best way to accomplish this is to select the right hardware and design in high performance and reliable components from the beginning.

C & K http://www.ckswitches.com/

Overload conditions can cause equipment to draw more power to work properly, which in turn, generates additional amounts of heat. If unchecked, excessive amounts of heat over a certain time period can damage the equipment or even cause a fire. Short circuits happen quickly and can result in equipment damage or even loss of life. In addition, technicians and maintenance personnel also need a way to energize and de-energize equipment for maintenance or modifications.

In addition to maintaining safe conditions, it’s also important to consider the financial implications of improper power protection, which can stem from failure to safeguard expensive equipment, the cost of unscheduled downtime, and constant maintenance or troubleshooting. In order to protect and control different types of electrical equipment within a factory or building, various types of circuit protection devices are used. Depending on the end

equipment requirements and the amount of power being used, these devices can include motor protection relays and contactors, motor starters, molded case circuit breakers, and air circuit breakers.

Protecting Electrical Equipment, Small and Large With over 50 percent of the work in a modern factory being completed by electric motors, it’s important that these devices have protection from electrical faults. Motor circuit breakers and overload relays are used at the electrical control cabinet level to protect single and three-phase motors from overload, locked rotor, and short circuit conditions, as well as de-energize equipment for maintenance reasons. These devices are used in applications with lower power motors, such as pumps, fans, conveyers, and machinery. Circuit breakers in general are designed to protect electrical circuits from damage caused by excess current and automatically interrupt current flow after a fault is detected so

problems can be addressed and service can resume quickly. Overload relays protect a motor by sensing the current going to the motor. Older products often used bi-metallic elements that reacted to heat from increasing current levels, however newer electronic relays monitor motor conditions using current transformers and internal circuitry. These products typically use rotary switches to adjust trip settings such as current and time delays.

Moving up to higher power requirements, molded case circuit breakers (MCCB) are used to protect large motors, generators, and welding equipment, as well as to protect and de-energize feeder circuits and main electrical panels for large machinery. An MCCB provides both overload and short circuit protection by combining a temperature sensitive device with a current sensitive electromagnetic device, to guard against conditions such as thermal overloads, short circuits and ground faults. Modern devices also have the capability to monitor energy usage and communicate remotely with control systems or enterprise level IT networks.

Moving up to even higher power applications, air circuit breakers are used to protect transformers, generators, and building and plant-level switchgear and power distribution systems. These devices are generally rated up to 690 VAC, can monitor energy usage, and have internal load

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Special Report:Industrial Power

Inside:

Intelligent Battery Monitoring...

Supercapacitors Come of Age...

Functionality Convergence in IIoT...

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39

42

36

SPECIAL REPORT : INDUSTRIAL POWER


Intelligent Battery MonitoringBy: Steve Applegate, Sales Director, Stadium Stontronics

Knowing Battery Charge and Health Data in Real-time

In our electrified world, we have become accustomed to continuity. If an airline scheduling system goes

down due to a power outage or our electric vehicle runs out of charge unexpectedly, we’re outraged. Battery systems providing backup and motive power should have guaranteed availability; but how is this ensured and measured?

Perhaps we’ve been spoilt by the apparent robustness of our tradi-tional lead-acid car batteries. It’s not unusual for them to last more than ten years with no fancy health monitoring or charge control. However, occasional peak current to crank an engine followed by regular continuous float charg-ing from an alternator is quite a benign situation. Batteries that stay inactive for long periods on standby, or which have to regularly discharge deeply, are in another category. Monitoring and control of their charge and discharge cy-cles is vital for longest service life and knowledge of state of charge. Knowing their ability to deliver that charge at a certain time is a measure of state of health and is equally important.

Lead-acid and Li-ion are similar in some ways

Lead-acid cells are a good exam-ple. To get optimum performance, the cells should always be fully recharged after every discharge with a limited current initially then a ‘saturation’ charge at fixed volt-age between 2.3 and 2.45 V/cell. This is followed by a ‘float’ charge between 2.25 and 2.27 V/cell de-pending on temperature. During the saturation phase, the current eventually drops to about 3 -5% of the amps in the amp-hour rat-ing, at which point the battery is fully charged. The float charging then makes up for the significant self-discharge of the battery. The saturation charge voltage is quite critical: too low and maximum capacity is not reached and there is a risk of sulfation on the nega-tive electrode; too high and inter-nal corrosion occurs with gassing and water loss. All these effects depend on temperature with the optimum charge voltage varying by 3 mV/oC, reducing above 25oC,

and increasing below.

Lithium-ion cells are similar to lead-acid in some ways: they are charged at constant current until the terminal voltage reaches typi-cally 4.2 V. There is only about 50 mV tolerance to this figure and it must not be exceeded otherwise catastrophic failure can occur. It is so critical that lithium-ion cells have built-in protection electron-ics to limit the voltage. Unlike lead-acid, Li-ion cells are not float charged: this would cause plating of metallic lithium so the charge current is terminated when it subsides to about 3 to 5% of the cell amp-hour rating. There is some small self-discharge over long periods in part because of the built-in protective circuit but this is countered with brief ‘topping up’ cycles. Also, unlike lead-acid, it is not necessary or even desirable to take Li-ion to full charge. Using the maximum allowable voltage

applies stress while aiming for a lower voltage extends cell life but at the expense of run time. See Fig-ure 1. Industrial and critical appli-cations will take the reduced stress route while consumer products are more focussed on run time.

An intelligent battery charger will take into account all of the criti-cal conditions to get maximum life and run-time from a battery. The most comprehensive systems for Li-ion automotive applica-tions might have eight or more controlled charging stages in a programmable profile with sen-sors monitoring voltage, current and ambient and cell casing tem-peratures to apply the appropriate corrections.

‘Batteries have complex person-alities’Having worked to charge a bat-tery in the most benign way, it is a different matter to measure its state of charge at any point. We have all watched in dismay as our

cell-phone charge percentage goes from 50 to zero within minutes; so why is it so inaccurate?

Batteries of all types have dynamic and complex personalities that de-pend on manufacturing tolerances, age and temperature and how they have been used or misused in the past. Cell voltages give a very poor indication of anything other than ‘empty’ or ‘about full’. And worse, after significant charge or dis-charge, cell voltages need a period of ‘relaxation’ of up to 24 hours to settle to a constant value. Even the definition of ‘fully charged’ has a different meaning over time, for example a lead-acid battery goes through a formatting process, actually increasing its amp-hour capacity at full charge over the first few hundred discharge cycles, peaking then eventually falling again depending on depth of dis-charge cycles. See Figure 2.

State of charge can be gauged in different ways. For ‘flooded’ lead-

Figure 1: Typical Charge Characteristics of Li-ion (Source: battery university)

Figure 2: Capacity and Cycle Life in Relation to Depth of Discharge (DOD)

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acid types, a sure way is to mea-sure the specific gravity of the electrolyte but for sealed types this is not an option. Another possibility to measure state of charge is to cycle the battery to full discharge and then charge with a measured amount of energy. This can damage lead-acid cells but is viable, if slow, for other chemistries. This ‘coulomb counting’ can be accurate but being an integrating technique, it accumulates errors and has to be regularly re-calibrated.

For any battery, capacity at full charge also depends on tempera-ture. For example, most battery types at -20oC have only around 50% of their 25oC amp-hour ca-pacity.

State of charge is not state of healthKnowing cell voltage and tem-perature with perhaps ‘coulomb counting’ can give an idea of state of charge. State of health, or capacity at full charge, can be estimated from the internal resis-tance of the battery cells but is a relative measure. It has been seen that internal resistance of new

lead-acid batteries can vary by eight per cent or more, so measure-ments have to be referred back to the ‘new’ value to be of use. With that knowl-edge, it can be said that a 25% increase in resistance might lead to an overall drop in

capacity of 20% from new. The rate of capacity loss over time is approximately linear; for example, lead-acid capacity decreases at a rate of about 0.25% per month after the formatting period.

Measuring internal resistance can be done in more or less sophisti-cated ways. An equivalent circuit of a battery is given by the ‘Ran-dles’ model, as shown in Figure 3.

CBULK is the main energy stor-age, RD is the self-discharge resistance, RTS is the resistance of the electrolyte solution and mechanical connections, RCT is the polarisation resistance of the electrodes, and CPE is a surface capacitance of the electrodes.

RCT is a critical measurement for state of health but a simple DC resistance check by measuring voltage drop at two different cur-rents only yields the combination of RCT and RTS. RTS has been shown to be a poor indicator of state of health, so a way to sepa-rate out the values is by injecting current at high frequency where CPE becomes low impedance, shorting RCT, leaving just RTS

and by subtraction from the DC test, giving RCT.

An even more accurate measure is given by injecting a range of frequencies at low voltage and measuring resultant current amplitude and phase data - the Electrochemical Impedance Spec-troscopy (EIS) method. Calibra-tion over a range of batteries of different known ages builds up an accurate model, which can be used for both state of charge and state of health.

The future promises more exotic techniques still with non-invasive measurements such as magnetic susceptibility of the electrode ma-terial or even refractive index of the electrolyte giving indications of state of charge.

Knowledge is powerThe ideal is to have charge and health data available in real-time, so communications is important. State-of-the-art battery manage-ment systems are smart and connected digitally. CAN bus, SPI bus, USB and wireless communi-cations are increasingly used to give that all-important reassur-ance that you really do have those miles left ‘in the tank’.

Stadium Stontronics sells a range of intelligent battery chargers and can design and manufacture cus-tom battery charging and moni-toring systems.

Stadium Stontronicshttp://stontronics.com/

Figure 3: "Randles" model of a battery

Supercapacitors Come Of AgeBy: Kunio Nomura, Product Manager - Capacitors, Murata

The Role that Supercaps will Play in Design of Future Energy Systems?

Within just a few years, devices that previously housed no electronics –

let alone information processing capabilities – have become increasingly ‘smart’, joining the Internet of Things. To fully realise the benefits of IoT, intelligent device performance levels and functionality have increased exponentially.

Increased functionality, however, means more complexity and the higher power-draw that entails. Engineers have gone to great lengths to minimize watts dissipated with dynamic modes of operation such as putting a device to ‘sleep’ when processing demand is low, but there are some functions that need bursts of power, such as wireless communications or a flash from

an LED. It’s not just micro-power circuits that need this function; devices that include small motors, smart meters and audio amplifiers for example all need this feature of peak power capability without a size or cost overhead.

To size the device battery for these peak loads is inefficient, bulky and expensive, so some form of peak load-levelling is desirable. This is where supercapacitors come in.

A traditional lithium or alkaline battery has been a solution, but the technologies have their limitations. Compared with batteries, a ‘supercap’ has much higher power density, up to 100,000 times more than a Li-MnO2 coin cell for example. The supercap wins hands-down for relatively high power for long periods, and is an order of magnitude better than the

closest battery performance – see Figure 1.

There are different form-factors of supercaps for different applications, ranging from coin-cell to cylinder and laminate types in order of peak current rating – see Figure 2. The laminate types in the DMT and DMF series from Murata are typical for use in load-levelling applications.

The particular performance of a supercap comes from its construction. It has no dielectric like other capacitor types, but an Electrical Double Layer (EDL). This is formed from an interface of active carbon powder and an electrolyte. The storage of charge is not by a chemical process but by the physical movement of ions to the pores in the carbon layers. The pores provide a huge surface

Figure 1: Power comparison of Murata’s supercapacitors with various battery technologies



area for charge to accumulate, giving capacitance values in excess of 1 Farad at 5 V rating. Equivalent Series Resistance (ESR) values are moderate, typically 50 to 500 milliohms, effectively making the capacitors short-circuit-proof. Compared with a battery, the supercaps only store about 10 Joules of energy, which generates no stress or significant heating effect on the part even under short-circuit conditions.

Another feature of supercaps is the virtually unlimited number of charge and discharge cycles allowed compared with finite numbers for batteries. Lifetime is long, with temperature and applied voltage being accelerating factors. Under controlled conditions, however, the parts can easily give far more than five years of useful service. Any concern about moisture ingress is addressed by the laminate construction, with its minimal size of resin seal. Like

Figure 2: Supercapacitor packageselectrolytics, the temperature range for supercaps is -40°C to +70°C or +85 °C with similar ESR variation at low temperatures.

Supercaps are polarized and available up to about 5 V rating. In fact, the typical DMT and DMF series from Murata are already two ‘units’ in series. Higher voltages can be easily achieved with series connection of the parts, with passive or active voltage balancing schemes. Paralleling is also easy with no special precautions necessary to achieve more energy storage. Charging is as quick as an electrolytic capacitor from a simple voltage source.

Another significant benefit is the ultra-slim form factor of the Murata DMT and DMF series, which are only 2.2 mm, matching the demands of today’s ‘pocketable’ and wearable electronics.

Muratahttp://www.murata.com

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Functionality Convergence in IIoT

By: Muhammad Shafique, solution architect, Mentor a Siemens company

A key challenge when enabling convergence is competing requirements of discrete functions on an SoC

Today’s Industrial Internet of Things (IIoT) is rapidly changing how

connected devices are enabled in modern heterogeneous multicore system-on-chip (SoC) architectures. These multicore environments reduce operational and maintenance costs by converging what were previously multiple discrete functions on a separate processor into a single, multi-functional SoC. But a major obstacle when enabling this type of convergence is often the competing requirements of various discrete functions such as safety certification, real-time response, UI/HMI, and network connectivity to name a few. This article discusses various ways discrete functions can be isolated on a single piece of silicon using technologies that include hypervisors, Arm TrustZone, and a multicore framework.

The industrial robotic armIn the past, embedded control systems were designed using a single processor with one function in mind. Today, in order to achieve complete

system control multiple discrete processors must be connected together.

To understand this better, let’s use an industrial robotic arm as a system available commercially as a standalone unit. In addition to the mechanical arm, it includes an electronic control unit and HMI display. The HMI enables manual operation or by programing a sequence of moves (script), it can perform without human intervention. In a real-world scenario this type of operation might include stacking items as they exit an assembly line.

In addition to the HMI and process control, the robotic arm controller implements safety interlocks. These interlocks can be used to shut down robotic arm operation in case of emergency and are programmed to various types of sensors e.g., proximity switches, pressure sensors, safety beam, etc. And because this is an IIoT enabled unit, it must also connect with an external network infrastructure. So we can add a fourth processor to perform network communications and

handle the firewall and various other associated activities. It’s important to note that each single function has different processing needs, and consequently, each function requires a different type of processor.

• HMI/Operator Console: A high-end application processor with rich graphics support such as an Arm Cortex-A with GPUs.

• Process Controller: Requires a high-end processor with use-case specific features. It could be a DSP if the primary function involves processing large amounts of data. Processors: Arm Cortex-A, Cortex-R, or a DSP core.

• Safety Controller: Requires a relatively low-end processor as the sole purpose of this controller is to execute safety interlocks. The Arm Cortex-R or Cortex-M are good candidates. Software running on this processor typically needs to go through safety certifications such as IEC 61508.

Figure 2: Mentor’s multicore framework approach which helps to utilize and manage multiple available homogeneous or heterogeneous cores on a multi-core processor.

• Network Controller: The

processor may have some additional networking communication capabilities e.g., radio or communication interfaces to talk with other IoT nodes, etc. Processors: Arm Cortex-A or Cortex-M.

Granted this is fairly simplistic view of an industrial robot unit with four processors, with each processor responsible for a discrete function. It is perfectly fine to realize this design in this discrete way. It will require building multi-processor PCBs or multiple PCBs, defining communication architecture between the processors, and integration testing at both the hardware and software levels.

Multicore development – not always about performanceEmbedded software has seen a proliferation of multicore SoCs. There are obvious situations where embedded systems need more computational power (e.g., network throughput for richer UI graphics), but in most situations, it’s more about reliability, responsiveness, power consumption, cost effectiveness, and maintenance over an extended period of time.

So what is the primary factor for using multicore in embedded? The answer is – convergence of functionality. Convergence means combining different forms/components of technology into a single entity.

From our robot example, if there is a way to utilize a single multicore processor to perform

“Safety Controller”, “HMI/Operator Console”, “Process Controller”, and “Network

Figure 1: Example of Arm’s TrustZone technology demonstrating compart-mentalization.



Controller” significant cost savings would be achieved in BOM and in hardware. Embedded devices typically have a long life and reduced BOM means fewer hard components to track and inventory over the lifespan of a device. The key challenge in multicore convergence is to maintain individuality of each discrete function. When looking at the robotic arm scenario, the processor used for the Safety Controller does not require much computational power. The most important requirement is to reliably read data from safety sensors and drive related actuators when needed. The code executing safety functions is typically subject to compliance requirements (IEC 61508 for industrial or ISO 26262 for automotive). On the other hand, the HMI/Operator Console requires a more computationally capable environment supporting rich graphics frameworks or multimedia capabilities with no safety requirements.

If we want to use one multicore processor to implement both Safety Controller and HMI/Operator Console functions we need strong compartmentalization, or a partitioning mechanism that can create different execution context; one high priority context for Safety Controller and another context for HMI (which is less critical). It’s important to make sure that non-critical code executing the HMI does not interfere or block any of the functions of the Safety Controller at any time.

Various technologies that enable isolation/compartmentalization include:

- Embedded HypervisorOften a hypervisor is the first thing that comes to mind as this type of technology has been the convergence enabler for the desktop and server domains. With virtualization extensions now available on multicore SoCs, this is certainly an option. A hypervisor is a software component that creates an abstraction on top of hardware, allowing multiple guests operating systems to

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Figure 3: This robot application leverages Arm TrustZone hardware extensions to realize a mixed-critical environment on single SoC where real-time safety functions are isolated from the HMI context. run simultaneously side by side.

- Arm TrustZoneThe Arm TrustZone (Figure 1) can run a secure operating system (secure world) and a normal operating system (normal world) at the same time from a single core or multiple cores, thus enabling a form of compartmentalization. TrustZone is hardware-based feature where software running in normal world is blocked from accessing secure world resources directly.

- Multicore FrameworkProcessing cores running in an asymmetric multiprocessing (AMP) configuration can help assign individual functions to various cores. A multicore framework (such as Mentor’s

framework depicted in Figure 2) assists with life cycle management and helps facilitate communication between various participating cores, which can be very useful.

Putting it all togetherTo illustrate embedded multicore enablement and convergence, let’s revisit the automated robotic arm. The robotic arm is a giant machine capable of performing heavy duty tasks. While the robotic arm is moving we do not want any human presence in the work area as this could create a hazardous situation. To avoid unsafe situations, we introduce safety beam safety interlocks where a laser beam cordons off the entrance to the robot work area. If anyone enters the area

and obstructs the safety beam, the robotic arm quickly stops moving and latches into a safe position.

When the safety beam is broken, in addition to latching the robot into a safe position, the system generates an alarm on HMI/Operator Console so that a corrective action can be taken.

If we take the traditional approach to architecting this type of system, we use one discrete processor to drive the HMI/Operator Console, one processor to control the robotic arm, and another processor to implement the safety domain.

However let’s follow a multicore SoC approach to better demonstrate system convergence.

First, we select the NXP i.MX6 homogeneous quad-core processor to implement the system. Figure 3 depicts how this system is constructed at a higher level.

Each of the TrustZone partitions is running an independent instance of Mentor’s Nucleus RTOS. Nucleus utilizes Arm TrustZone technology and the OpenAMP-based multicore framework to do life cycle management and enable communication between secure and normal worlds. The secure world Nucleus application is responsible for

the safety beam functionality and rendering safe graphics on the HMI/Operator Console. This is called the “Safety Domain” and is represented by the red dotted line in the shaded box in Figure 3. Whenever secure world Nucleus detects safety beam obstruction via laser detector it sends a command to the robot to stop moving and enters into an alarm state. Real-time status of safety beam and alarm state is animated on the HMI/Operator Console.

The normal world Nucleus application is used for the user interface to drive the robot and control its movement. This application also provides information on robot movement.

Notice that both secure and normal world Nucleus applications are rendering on a single display unit (HMI/Operator Console). This implementation uses layered graphics architecture with safe graphics overlaying on top of non-safe graphics.

As the secure world has higher priority over normal world, the safety functions are always available, even if the normal world is shut down or corrupted.

So in effect, we have a single i.MX6 SoC fulfilling rich graphics, real-time control, and safety functions at the same time without compromising any of the discrete functions

i.e., acting as both a Safety Controller and HMI/Operator Console.

ConclusionThe converged software architecture brings significant benefits and cost savings. It is possible to combine safe and non-safe software on multicore SoCs by using technology components such as hypervisors, multicore frameworks, and Arm TrustZone. These components help maintain individuality of discrete functions and provide the much needed isolation.

Mentor Graphicshttps://www.mentor.com/

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POWER SYSTEMS DESIGNFINALthought

By: Ally Winning, European Editor, PSD

Small decisions, large consequences

Design is always a tricky

business, and sometimes

its the most innocuous

things that provoke the

largest outcry. There have been many

instances in the past when a simple

design decision, which has been made

for the most logical reasons, turns into

a nightmare on launch.

Perhaps the most famous of these

snafus came last year, when Apple

launched its iPhone 7. Almost all the

fanfare from the launch was drowned

out by the outcry from the company’s

customers. Apple had dropped the

earphone jack from the product. For

many of the people who had stuck

with Apple products through some

previous controversial design choices,

this was a step too far.

The ear buds were synonymous with

the iPhone and iPod. The distinctive

white buds became a symbol of the

brand and were even used prominently

in the company’s advertising. People

could immediately identify an iPhone

owner by their earphones. The media

even informed us that muggers were

targetting potential victims by the

easily identifiable earbuds they wore.

Why would Apple drop this iconic

symbol in favour of two expensive

wireless buds, which would easily be

lost?

Of course, if buds are misplaced,

customers will have to return to Apple

for replacements, but that wasn’t the

main reason for the initial decision.

Water ingress is the reason for the

majority of phone failures, and it is

extremely difficult to prevent it when

your design has holes in it that lead

directly to the internal electronics.

Plugs can be used to prevent ingress,

but this can mess up an elegant

design. Take the socket out and you

can easily seal the phone. The iPhone

7 is certified to IP67, meaning that it

can actually be submerged in a meter

of water for 30 minutes, which should

actually have been a major selling

point for consumers. It also brings

the bonus that the design is more

structurally sound, and it allows for a

more compact and flexible design.

Apple has always been bold with its

design choices and the company’s

decisions can affect the whole market.

If there’s not a standard that can fit

the purpose Apple requires, then the

company knows that it can create its

own, and it has a huge user base that

will normally buy in great numbers.

If there is a standard that will fit the

purpose, then Apple will adopt it,

even if it hasn’t been widely adopted

by the industry. USB 3.0 is a good

example of this type of choice. Apple

picked USB 3.0 from almost obscurity,

when it announced it would it as the

only socket in its MacBook Air and

MacBook Pro ranges. Third party

vendors stepped up with peripherals

and the adoption of the standard grew

exponentially.

The iPhone 8 is due for launch, and

if the industry rumours are true, it

looks like the only controversial design

choice this time is the decision to leave

out the home button. I’m sure Apple

executives are holding their breath to

see how the once loyal, but now fickle,

customer base reacts. The loss of a

button doesn’t seem too controversial,

but just ask Microsoft the reaction it

got when it dropped the start button

from its Windows 8 software.

PSD


VISIT http://www.ieee-ecce.org/2017/registration/online-registration

[email protected]

with any questions regarding registration

CONFERENCE October 1-5, 2017

EXPOSITION October 2-3, 2017

Registration Is Live!

Linear Technology ASM STANDARD PAGE TRIM SIZES : 8 x 10.5” Minimum 8.5 x 11.25” / 216mm x 286mm Maximum

Agency contact: Jon MiwaPhone: 926-642-3053Email: [email protected]

Info & Online Store Features

, LT, LTC, LTM, Linear Technology, the Linear logo,and µModule are registered trademarks of Analog Devices, Inc. All other trademarks are the property of their respective owners.

www.linear.com/product/LTC71031-800-4-LINEAR

• 4.4V to 105V Input Voltage Capability• High Efficiency Synchronous

Monolithic: Up to 94% Efficiency• Low EMI/EMC Emissions: CISPR25,

Class 5 Compliant• Accurate Output Current Limiting/

Monitoring• Ultralow Quiescent Current• Switching Capability to 2MHz• Small/Simple/High Current Capability

Efficiency vs Load Current

3.3V @ 2.3A

4.4V to105V

ICTRL

IMON

LTC7103

IQ = 2μAIQ = 2μA

100

95

90

85

80

75

70

65

60

55

500.1 1 10 100 1000

LOAD CURRENT (mA)

EFFI

CIEN

CY (%

)

VOUT = 5V

VIN = 12VVIN = 24VVIN = 48VVIN = 72V

fSW = 300kHz

The LTC7103 combines 100V input capability, synchronous rectification and an ultralow EMI design, providing a compact 2.3A step-down solution. It delivers up to 94% efficiency while offering a compact solution footprint for high voltage applications such as emerging 48V automotive, transportation and telecom systems. Its unique design offers ultralow EMI/EMC emissions, easily meeting CISPR25 Class 5 limits. The LTC7103 also implements fast and accurate output current programming and monitoring without an external RSENSE. It consumes only 2μA quiescent current and is in a 5mm x 6mm QFN package.

105V/2.3A Sync Buck

Ultralow EMI/EMC Emissions: CISPR25 Class 5 Compliant

Find your local sales office: www.linear.com/contact

Documents

October 2017 - Power Systems Design · versatile BBU-S is available with AC or DC input voltage and can charge and control multiple battery pack configurations. The BBU-S starts at