Fairchild Power Switch

Sep, 2004Power Conversion

Before AfterEach end device needsit’s own power supply.

Each end device getsit’s own power from the network.

External AC/DC Adaptor Built in DC/DC Converter

The Value Proposition of PoE

Almost all appliances require both data connectivity and a power supply. In a familiar example, telephones are powered from the telephone exchange through the same twisted pair that carries the voice. Now we can do the same thing with Ethernet devices.

So why bother? Here are some reasons:

• Only one set of wires to bring to your appliance - simplifies installation and saves space.

• There is no need to pay for an expensive electrician, or delay your installation to meet the electrician's schedule - saves time and money.

• The appliance can be easily moved, to wherever you can lay a LAN cable - minimal disruption to the workplace.

• Safer - no mains voltages anywhere.

• A UPS can guarantee power to the appliance even during mains power failure.

• As well as the data transfer to and from the appliance, you can use SNMP network management infrastructure to monitor and control the appliances.

• Appliances can be shut down or reset remotely - no need for a reset button or power switch.

• In wireless LAN systems it simplifies the RF survey task, as the access point can easily be moved and wired in.

The Motivation for Power over Ethernet

Already manufacturers have products on the market. Many of these are described in the Products section of the www.PowerOverEthernet.com website. There is no shortage of the Power Sourcing Equipment Midspan Hubs, so you can start playing with the technology now. The big market players are using it for these applications:• VoIP (Voice over Internet Protocol) telephones. • IEEE802.11 Wireless LAN Access Points. • Bluetooth Access Points. • Web cameras.

But Power Over Ethernet will enable many more appliances. Here's a list - but you can imagine others!• Smart signs/web signs. • Vending machines. • Gaming machines. • Audio and video juke boxes. • Retail point of information systems. • EPOS systems. • Building access control systems. • Time and attendance systems. • Battery chargers for mobile phones and PDAs. • Electronic musical instruments.

Some Possible Uses of the Technology

The user would merely have to plug the devices into a traditional Category-5, Ethernet-cable wall socket.

Power-over-Ethernet(PoE) LAN switches

Power Supplied over the Spare Pins

RG-45Switch End

RG-45DTE end

Cat5 cable

RG-45DTE end

RG-45Switch End

Normal legacy network

The power for Power-over-Ethernet devices can be supplied through the spare wires of a typical CAT-5 cable. This is supported by the standard.

How PoE is done

Description• The FS6X1220R is a high voltage power

switching regulator that combines the required converter functions with allowing a simple power system solution for DC-DC converters

Features• Optimized for Off-line type DC to DC Converter• High switching frequency for good efficiency

(300KHz)• Line UVLO monitoring and Sleep on/off• Various protection functions (OVP, OLP, TSD)• Auto restart mode• TO-220F-5L / D2-PAK-5L• Over 80% Efficiency Low Rds(on) QFET minimizes conduction

losses Low capacitance QFET cuts switching

losses

FS6X1220R

9V

15V

Vcc

Vds

• During start up, the power is supplied to Vcc pin from DC link through startup resistor.

• When Vcc reaches the UVLO upper threshold, the power is supplied from auxiliary transformer winding.

9V/15V

3

VrefInternal

Bias

Vcc

Vcc good

VDC

Vc

Rstart

Start-up

Optimized Feedback for off-line DC/DC converters

Current Mode PWM IC

2

4

S

Q

Q

R

OSC

Vcc Vref

Idelay IFB

R

28RFB

GND

Gatedriver

LEB

PWMVx

Vx

VFB

Feedback for off-line DC/DC convertersFeedback for off-line DC/DC converters

Shutdown7.5V

V

tt1 t2

•Time Constant : 5uA = Cfb * 4.5V / t2

0

3V

OSC.

LEB

5uA 1mA

2.8R

R

Voffset

SQ

R

Vck

FPSTM

FB

Vfb*

7.5V

SQ

R

Vo

Cfb

ThermalShutdown

ResetShutdown

Secondary Side

• Consider the load current increasing significantly• FPSTM increases its duty cycle within the limits of its pulse-by-pulse current limit• Output voltage falls and the feedback voltage rises• If just a momentary surge then the output will rise after the surge and the feedback voltage will resume its steady state• However, if output is shorted to ground, then feedback voltage continues to rise• At 3V, feedback voltage is pulled up with a small internal 5µA current allowing for adjusting the delay as shown above• When feedback voltage crosses the over-load shutdown (VSD) threshold, the FPS stops switching• With FPSTM not switching, no bias current is supplied and supply Vcc will fall• When the Vcc voltage reaches its “Under Voltage Lock Out” threshold, the FPSTM is automatically restarted• The cycle will repeat until the fault condition is removed.

Features: Over Load Protection

OSC.5uA 1mA

2.5R

R

S

QR

Vck

FS6X1220RT

Vfb*

7.5V SQ

R

ThermalShutdown

ResetShutdown

Vcc

Vovp

Vcc

Protection for over voltage Auto restart mode

Over Voltage ProtectionOver Voltage Protection

9V/15V

3

Vref

InternalBias

S

Q

Q

R

Vcc

Vcc good

OLP

OVP

LineUVLO

OTP

Stopswitching

Auto-restart : protection latch is automatically reset when Vcc < 9V

Fault situation

9V

15V

Vcc

Vds

Icc

10mA

60uA

t

Fault occurs Fault

removed

Normal operation

Normal operation

Poweron

Auto Restart

VSL(1.8v)

VLU(2.5V)

9V/15V

3

5

Vref

Line UVLO

Enable

InternalBias

Vcc good

LineSense

VccVin

R1

R2

SleepON OFF

Line UVLO mode (VLS<2.5V): operating current = 10mA Sleep mode (VLS<1.8V): operating current = 300uA Startup current : 60 uA

Sleep mode and Line UVLO

Input = 36VPin Efficiency

Io Vo Po

1A 3.362V 3.36W 4.14W 81.13%

2A 3.357V 6.71W 7.64W 87.91%

3A 3.351V 10.05W 11.31W 88.92%

4A 3.345V 13.38W 15.02W 89.08%

5A 3.338V 16.69W 18.66W 89.45%

6A 3.362V 20.17W 22.78W 88.55%

Input =48V PinEfficiency

Io Vo Po

1A 3.374V 3.37W 4.58W 73.72%

2A 3.369V 6.74W 8.20W 82.20%

3A 3.363V 10.09W 11.89W 84.88%

4A 3.355V 13.42W 15.67W 85.67%

5A 3.345V 16.73W 19.53W 85.63%

6A 3.334V 20.00W 23.57W 84.87%

Input =60VPin

EfficiencyIo Vo Po

1A 3.378V 3.38W 4.80W 70.33%

2A 3.373V 6.75W 8.57W 78.73%

3A 3.365V 10.10W 12.22W 82.62%

4A 3.357V 13.43W 16.01W 83.86%

5A 3.346V 16.73W 19.87W 84.21%

6A 3.334V 20.00W 23.84W 83.91%

Input =72V PinEfficiency

Io Vo Po

1A 3.381V 3.38W 5.09W 66.41%

2A 3.375V 6.75W 8.97W 75.28%

3A 3.368V 10.10W 12.67W 79.73%

4A 3.359V 13.44W 16.45W 81.70%

5A 3.346V 16.73W 20.31W 82.37%

6A 3.335V 20.01W 24.25W 82.52%

Measured EfficiencyMeasured Efficiency

FS6X1220R Efficiency

50.00%

55.00%

60.00%

65.00%

70.00%

75.00%

80.00%

85.00%

90.00%

95.00%

1A 2A 3A 4A 5A 6AOutput Current

Effi

cie

ncy

Input = 36VInput = 48VInput = 60VInput = 72V

Measured EfficiencyMeasured Efficiency