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Connecting input and output devices to electronics.

prepared by Prof. George Slack (EE)prepared by Prof. George Slack (EE)

Copyright © 2006 Rochester Institute of TechnologyAll rights reserved.

Practical Design Considerations Practical Design Considerations I/O CircuitsI/O Circuits

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Start your schematic(s), if not already. Sketch a drawing or visualization your project including the

following:• Interface Devices• ALL inputs and outputs (don’t stop at the board’s edge!)• power On/Off, reset and safety switches, sample select switch • removable AC power cord• connectors • harnesses (& cables) • board(s)

– test points – LEDs (more is better)– Jtag, USB, RS232, Ethernet (may not need the form factor)– accessory power connectors

Prerequisite: Schematic Guidelines

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Steps in Designing I/O CircuitsSteps in Designing I/O Circuits

Step 1. Interface SpecificationsStep 1. Interface SpecificationsStep 2. Specification Sheets & Application NotesApplication Notes

Step 3. Analysis I/O Step 3. Analysis I/O

Step 4a. Synthesis Output DevicesStep 4a. Synthesis Output Devices

Step 4b. Synthesis Input DevicesStep 4b. Synthesis Input DevicesStep 5. Analysis Noise immunity

Step 6 Analysis Harness Signal ResponseStep 6 Analysis Harness Signal Response

Step 7 Connectors/ Pins

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Step 1: Interface SpecificationsInterface Specifications

1.1. Bandwidth, frequency response; rf to dcBandwidth, frequency response; rf to dc

2.2. Data rateData rate

3.3. Analog versus digital (you should know by now)Analog versus digital (you should know by now)

4.4. Circuit protectionCircuit protection5. Power/ Current6. Voltage Levels: Vdd/Vcc, multiple?7. Devices (Vdd vary from 1.5 VDC to 18 VDC) 8. Output Control: Sink or source?9. Data Controls: enables, select lines, etc.10. EMI Noise11. Heat

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Step 2. Specification Sheets & Application NotesApplication NotesSave Hours of design time!Save Hours of design time!Exploit these Design Notes!Exploit these Design Notes!

1.1. Many Specification Sheets have recommended applications Many Specification Sheets have recommended applications that may apply directly to your design! Use them! that may apply directly to your design! Use them!

2. Not sure what you need? …. or researching components? http://cmpmedia.globalspec.com/

3. Manufacturer’s Home Pages4. Suppliers: DigiKey, Mouser and Allied offer good on-line

spec sheets5. http://www.findchips.com/ 6. Google (I must admit, I do this first….)

7. RIT Library services

8.8. If complex solution, don’t start from scratch! If complex solution, don’t start from scratch! • Purchase device evaluation/ demo kits (USB, Purchase device evaluation/ demo kits (USB,

Microcontroller, Motor controllers)Microcontroller, Motor controllers)

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(continued Examples)(continued Examples)

• CMOS (i.e. MicroController Interfaces) devices may need CMOS (i.e. MicroController Interfaces) devices may need protection electronics.protection electronics.

• Responsive to signal processing spec’s.Responsive to signal processing spec’s.• Example 1. PIC18F2455 Interface considerationsExample 1. PIC18F2455 Interface considerations

– See attached pdf.See attached pdf.

• Example 2. Freescale Semiconductor Inc - application Example 2. Freescale Semiconductor Inc - application schematicschematic– Motor Controller MC3PHACVDWMotor Controller MC3PHACVDW

If the spec sheet document is large, send me the link If the spec sheet document is large, send me the link and I will print for you. Soon may be 400 pages but and I will print for you. Soon may be 400 pages but DO IT!DO IT!

Acrobat Document

Acrobat Document

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Step 3. Analysis Step 3. Analysis I/O I/O

1.1. Impedance matching to your control electronicsImpedance matching to your control electronics

OutputsOutputs InputsInputs• Low Voltage to High CurrentLow Voltage to High Current Higher Voltage to Low VoltageHigher Voltage to Low Voltage• Low Voltage to High VoltageLow Voltage to High Voltage Higher Current to Low VoltageHigher Current to Low Voltage• Low Current to High CurrentLow Current to High Current• Low to Current to High VoltageLow to Current to High Voltage

2. Apply to Thevenin Equivalent Circuits– Source electronics– Device being driven– RLC loads (& potential for unwanted current and voltage

spikes)

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Step 4a. SynthesisStep 4a. SynthesisOutput DevicesOutput Devices

• LogicLogic: Microcontroller to input of electronics drivers.: Microcontroller to input of electronics drivers.• DriverDriver: (voltage to voltage, voltage to current.): (voltage to voltage, voltage to current.)• Device:Device:

– MotorsMotors– Linear ActuatorsLinear Actuators– SolenoidsSolenoids– Storage CapacitorsStorage Capacitors– HVPSHVPS– LEDsLEDs– HeatersHeaters

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cont.cont.Types of Output Driver ComponentsTypes of Output Driver Components

Matching (Voltage, Impedance, Current): Matching (Voltage, Impedance, Current):

ComponentsComponents– Transistor: Single stage and Darlington.Transistor: Single stage and Darlington.– JFETJFET– MOS FET MOS FET – IGBT DC to AC inverters (hybrid cars, mass transit)IGBT DC to AC inverters (hybrid cars, mass transit)

Devices:Devices:– Isolators: Optical DriversIsolators: Optical Drivers– H bridge: bi-directional control for DC Motors (See later slide)H bridge: bi-directional control for DC Motors (See later slide)

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Step 4b. SynthesisStep 4b. SynthesisInput DevicesInput Devices

DevicesDevices• Op AmpOp Amp• Isolator: Optical and MagneticIsolator: Optical and Magnetic• Level Shifter/ TranslatorLevel Shifter/ Translator

(other) Power (other) Power • RegulateRegulate• DC to DC convertersDC to DC converters– voltage boasting/ ± polarityvoltage boasting/ ± polarity– current boastingcurrent boasting

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Step 5. Analysis Noise immunity

• Circuit noise immunity is the ability of a device or component to operate in the presence of noise disturbance .

• Electro Static Discharge is the sudden discharge (i.e. transients, surge). To the circuit, this is a rapid high voltage, low current situation.

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5 Continued5 ContinuedWhere does noise get into electronics?Where does noise get into electronics?

• through ground connections and loopsthrough ground connections and loops• through power supply connectionsthrough power supply connections• through signal inputsthrough signal inputs• through inadvertent ESD through inadvertent ESD

– (human touch, lightning)(human touch, lightning)• through Inductive devices (motors)through Inductive devices (motors)

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5 Continued5 ContinuedHow does noise get into electronics? How does noise get into electronics?

Energy CouplingEnergy Coupling

(Conductive, Inductive, Capacitive)(Conductive, Inductive, Capacitive)• EMI - Current surgesEMI - Current surges

((EElectrolectroMMagnetic agnetic IInterference) An electrical disturbance in a nterference) An electrical disturbance in a system due to natural phenomena, low-frequency waves system due to natural phenomena, low-frequency waves from electromechanical devices or high-frequency waves from electromechanical devices or high-frequency waves (RFI) from chips and other electronic devices. Allowable limits (RFI) from chips and other electronic devices. Allowable limits are governed by the FCC.are governed by the FCC.

RFI – high impedance devices requiring very RFI – high impedance devices requiring very limited current.limited current.

((RRadio adio FFrequency requency IInterference) High-frequency electromagnetic waves nterference) High-frequency electromagnetic waves that emanate from electronic devices such as chips. that emanate from electronic devices such as chips.

If the source is sufficiently strong this can enter your circuit.If the source is sufficiently strong this can enter your circuit.

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Cont 5Cont 5ESD and unwanted signalsESD and unwanted signals

• Fatal to Electronics:Fatal to Electronics:• Inadvertent user misuse.Inadvertent user misuse.• Extreme cases of user abuse and solutions:Extreme cases of user abuse and solutions:

– Bridge to block reverse polarity,Bridge to block reverse polarity,– Schottky diode: very fast switching times and Schottky diode: very fast switching times and

low forward voltage drop. As low as 0.15 volts low forward voltage drop. As low as 0.15 volts for low ma applications. for low ma applications.

– Zener diode across the input. Zener diode across the input. – Circuit breaker – GFICircuit breaker – GFI

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5. Synthesis5. SynthesisCMOS gateCMOS gate

Reduce TransientsReduce TransientsProtect from?Protect from?• Misuse during debug and testing.Misuse during debug and testing.• ESD and reverse polarityESD and reverse polarity

– Solution: Diode circuits to protect against Solution: Diode circuits to protect against • reduce transientsreduce transients

– Component Specification SheetsComponent Specification Sheets– Solution: Low pass filterSolution: Low pass filter

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5. Isolating Noise5. Isolating Noise

• Analog and Digital Optocoupler /Optoisolators Somewhat Analog and Digital Optocoupler /Optoisolators Somewhat expensive ($1/ channel) but good isolation.expensive ($1/ channel) but good isolation.– an electronic device that uses optics to transfer a signal while an electronic device that uses optics to transfer a signal while

keeping the receiving and transmitting circuits electrically keeping the receiving and transmitting circuits electrically isolated .isolated .

– Analog Devices:Analog Devices:• http://www.analog.com (Analog Devices) (Analog Devices)• http://www.analog.com/en/subCat/http://www.analog.com/en/subCat/

0,2879,767%255F827%255F0%255F%255F0%255F,00.html0,2879,767%255F827%255F0%255F%255F0%255F,00.html• http://www.analog.com/en/prod/0,2877,ADuM2401,00.htmlhttp://www.analog.com/en/prod/0,2877,ADuM2401,00.html

– OPTO:OPTO:• http://www.optoinc.com/http://www.optoinc.com/• http://www.optoinc.com/optocouplers1.htmlhttp://www.optoinc.com/optocouplers1.html

Acrobat Document

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5 Example of Driver Circuit5 Example of Driver Circuit

•

Acrobat Document

• Driver Circuit – Opto Driver Circuit – Opto 22 ODC522 ODC5– See diagram below See diagram below

for application.for application.– Output Device – 2.5a, Output Device – 2.5a,

50 vdc Inductive Load50 vdc Inductive Load

Acrobat Document

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5. 5. Polarity Protection

+ Input Port–

(+)

(–)

+

Input Port

–

1N5822 or 1N5817

1N4001

Schottky diode

see 7.4.1 page 238, MOSFET solution

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5. 5. Over-voltage Protection

Fuse

1N5339 (5.6V for a 5.0V input)

+ input port–

(+)

(–)Zener diode(also MOV)

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5. 5. Over-voltage Protection for Digital Inputs

Vdd

Acrobat Document

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5. Minimize Bandwith5. Minimize BandwithOne solution: Lowpass FilterOne solution: Lowpass Filter

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5. CMOS and Noise5. CMOS and Noise characteristics Print out the specification sheets. characteristics Print out the specification sheets.

• 1 uA input? Not sure? Get the spec sheet!...1 uA input? Not sure? Get the spec sheet!...• Draw the equivalent circuit for each internal Draw the equivalent circuit for each internal

pin. That is, CMOS versus TTL input pin. That is, CMOS versus TTL input impedance, output is pull-up or pull-down impedance, output is pull-up or pull-down circuit, current limiting resistor value.circuit, current limiting resistor value.

• CMOS inputs have very high input CMOS inputs have very high input impedance which is good for low power impedance which is good for low power consumption for well protected electronics consumption for well protected electronics but susceptible to misuse when connecting but susceptible to misuse when connecting to the outside world. to the outside world.

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5. Decoupling Capacitors5. Decoupling Capacitors

• Know your performance response needs. Know your performance response needs. Try to eliminate frequencies outside your Try to eliminate frequencies outside your performance needs (i.e. filtering, smooth performance needs (i.e. filtering, smooth out spikes in DC power of IC’s). out spikes in DC power of IC’s).

• Common practice is to isolate IC’s with Common practice is to isolate IC’s with capacitors. See manufacturer’s Spec capacitors. See manufacturer’s Spec Sheet for capacitor values. Sheet for capacitor values.

• Filters current transients when transistors Filters current transients when transistors switch with a digital logic gate.switch with a digital logic gate.

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Step 6 AnalysisStep 6 AnalysisHarness Signal ResponseHarness Signal Response

Design Considerations: Design Considerations: data rate, distance, data rate, distance, noise, parasitic capacitance, reflections.noise, parasitic capacitance, reflections.

1.1. Frequency Response/ Rise Time needs Frequency Response/ Rise Time needs – DC to 100 khz Open Wire DC to 100 khz Open Wire – DC to 40 MB/s Ribbon Cable (less than 3’)DC to 40 MB/s Ribbon Cable (less than 3’)

• SCSI, SPI-3 applicationsSCSI, SPI-3 applications– DC to 300 mhz Twisted Pair - unshielded, DC to 300 mhz Twisted Pair - unshielded,

ribbonribbon– DC to 100/1000 MB/s 10/ 100/ 1000 BaseT DC to 100/1000 MB/s 10/ 100/ 1000 BaseT

ethernet Cat 5 minimum spec. RJ45 ethernet Cat 5 minimum spec. RJ45 connector.connector.

– Coax, VHF 3000 megahz (scope probe, cable Coax, VHF 3000 megahz (scope probe, cable TV) attenuation, reflectance, Cable TV, RfTV) attenuation, reflectance, Cable TV, Rf

– DC to 4 gigahz Fiber OpticsDC to 4 gigahz Fiber Optics

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Step 7 SynthesisStep 7 SynthesisHarness -Twisted PairHarness -Twisted Pair

When purchasing harness cable:When purchasing harness cable:• Unshielded Twisted Pair (UTP)Unshielded Twisted Pair (UTP)• Shielded Twisted Pair (STP) Shielded Twisted Pair (STP)

Study the manufacturer’s Specification to match to Study the manufacturer’s Specification to match to your needs.your needs.

Practical Design Considerations Practical Design Considerations http://www.cirris.com/testing/twisted_pair/twist.htmlhttp://www.cirris.com/testing/twisted_pair/twist.html

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Cont 7 Harness -Twisted PairCont 7 Harness -Twisted Pair

What is does: Cancels out crosstalk from neighboring wires What is does: Cancels out crosstalk from neighboring wires and electromagnetic interference from external sourcesand electromagnetic interference from external sources

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7 Practical Harness Considerations

1. Current, Voltage Needs• Gauge of wire, insulation

2. Use and Abuse • Connect/ disconnect needs • Routing, protecting• Mounting, vibration and stability• Gold versus Tin; environment, corrosion, current rating• Instrumentation quality for long life

3. Color Coding for ease in Debug and future use.As an example;1. Red Vcc/Vdd2. Black Grd/ Vss3. Org for signal

4. Fabricating: Harness board and nails

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8 Connectors/ Pins

Add all needed I/O connectors to your schematic(s).1. Connect/ disconnect needs – screw terminators, push type 2. Major Manufactures: Amp, Molex3. Location

– between assemblies– interface to other projects (collaborate with other

teams) – instrumentation

4. Get crimp compatibility to pin manufacturers (style and gauge).

5. Pins: crimp versus solder6. Current rating rule of thumb is 10x. i.e. 100 ma purchase

1 amp pins7. Types; ribbon, D shell, PCB mount

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Misc: (H Bridge Considerations)Misc: (H Bridge Considerations)

• Motors or whenever you need to direct current.Motors or whenever you need to direct current.• Introduction to H bridge operation:Introduction to H bridge operation:

– http://www.dprg.org/tutorials/1998-04a/http://www.dprg.org/tutorials/1998-04a/• Designing an H-Bridge and PWM Circuits and Code Designing an H-Bridge and PWM Circuits and Code

– http://www.learn-c.com/experiment7.htmhttp://www.learn-c.com/experiment7.htm• Debugging: Initial reset may close a short circuit or stress Debugging: Initial reset may close a short circuit or stress

on the H bridge. Symptom: Motor shaft may pulse or flinch on the H bridge. Symptom: Motor shaft may pulse or flinch at power on. May cause immediate failure.at power on. May cause immediate failure.

• Design Needs: Inductive loads and protection diode.Design Needs: Inductive loads and protection diode.

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• Start your schematic(s), if not already. • Sketch a drawing or visualization your project including the

following:• Define I/O Design NeedsDefine I/O Design Needs• Specification Sheets & Application NotesApplication Notes• Analysis I/O Analysis I/O • Design Output DevicesDesign Output Devices• Design Input DevicesDesign Input Devices• Consider Noise immunity• Harness; Signal ResponseHarness; Signal Response• Connectors/ Pins

Next Steps:• Define your core electronics and software development

Summary: