LTC4266IUHF#PBF - LINEAR TECHNOLOGY

LTC4266

4266fg

For more information www.linear.com/LTC4266

n High Power PSE Switches/Routers

n High Power PSE Midspans

ApplicAtions

FeAtures Description

Quad IEEE 802.3at Power

over Ethernet Controller

The LT C

4266 is a quad PSE controller designed for use

in IEEE 802.3 Type 1 and Type 2 (high power) compliant

Power over Ethernet systems. External power MOSFETs

enhance system reliability and minimize channel resis-

tance, cutting power dissipation and eliminating the need

for heatsinks even at Type 2 power levels. External power

components also allow use at very high power levels while

remaining otherwise compatible with the IEEE standard.

80V-rated port pins provide robust protection against

external faults.

The LTC4266 includes advanced power management

features, including current and voltage readback and

programmable ICUT and ILIM thresholds. Available C

libraries simplify power-management software develop-

ment; an optional AUTO pin mode provides fully IEEE-

compliant standalone operation with no software required.

Proprietary 4-point PD detection circuitry minimizes false

PD detection while supporting legacy phone operation.

Midspan operation is supported with built-in 2-event clas-

sification and backoff timing. Host communication is via

a 1MHz I2C serial interface.

The LTC4266 is available in a 5mm × 7mm QFN pack-

age that significantly reduces board space compared with

competing solutions. A legacy-compatible 36-pin SSOP

package is also available.

n Four Independent PSE Channels

n Compliant with IEEE 802.3at Type 1 and 2

n 0.34Ω Total Channel Resistance

n 130mW/Port at 600mA

n Advanced Power Management

n 8-Bit Programmable Current Limit (ILIM)

n 7-Bit Programmable Overload Currents (ICUT)

n Fast Shutdown of Preselected Ports

n 14.5-Bit Port Current/Voltage Monitoring

n 2-Event Classification

n Very High Reliability 4-Point PD Detection

n 2-Point Forced Voltage

n 2-Point Forced Current

n High Capacitance Legacy Device Detection

n LTC4259A-1 and LTC4258 Pin and SW Compatible

n 1MHz I2C Compatible Serial Control Interface

n Midspan Backoff Timer

n Supports Proprietary Power Levels Above 25W

n Available in 38-Pin 5mm × 7mm QFN and 36-Pin

SSOP Packages

typicAl ApplicAtion

Complete 4-Port Ethernet High Power Source

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and

ThinSOT is a trademark of Analog Devices, Inc. All other trademarks are the property of their

respective owners.

4266 TA01

VEE SENSE1 GATE1 OUT1 OUT2 OUT3SENSE2 GATE2 SENSE3 GATE3 SENSE4 GATE4 OUT4

PORT1

–54V

0.22µF 100V

×4

S1B

×4

S1B

×4

PORT2

PORT3

PORT4

INT

SHDN1 SHDN2 AUTO MSD RESETSHDN3 SHDN4 MID SDAIN SCLAD3AD2AD1AD0

LTC4266

VDD

DGND

AGND

–54V

1µF

100V

SMAJ58A

0.1µF

SMAJ5.0A

10Ω

3.3V

10µF

CBULK

TVSBULK

SDAOUT

LTC4266

4266fg

For more information www.linear.com/LTC4266

Absolute MAxiMuM rAtings

pin conFigurAtion

orDer inForMAtion

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC4266CGW#PBF LTC4266CGW#TRPBF LTC4266CGW 36-Lead Plastic Wide SSOP 0°C to 70°C

LTC4266IGW#PBF LTC4266IGW#TRPBF LTC4266IGW 36-Lead Plastic Wide SSOP –40°C to 85°C

LTC4266CUHF#PBF LTC4266CUHF#TRPBF 4266 38-Lead (5mm × 7mm) Plastic QFN 0°C to 70°C

LTC4266IUHF#PBF LTC4266IUHF#TRPBF 4266 38-Lead (5mm × 7mm) Plastic QFN –40°C to 85°C

Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.

Consult LTC Marketing for information on non-standard lead based finish parts.

For more information on lead free part marking, go to: http://www.linear

.com/leadfree/

For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through

designated sales channels with #TRMPBF suffix.

TOP VIEW

GW36 PACKAGE

36-LEAD PLASTIC WIDE SSOP

TJMAX = 125°C, θJA = 80°C/W

RESET

MID

INT

SCL

SDAOUT

SDAIN

AD3

AD2

AD1

AD0

DGND

VDD

SHDN1

SHDN2

MSD

AUTO

OUT1

GATE1

SENSE1

OUT2

GATE2

SENSE2

VEE

OUT3

GATE3

SENSE3

OUT4

GATE4

SENSE4

AGND

SHDN4

SHDN3

13 14 15 16

TOP VIEW

UHF PACKAGE

38-LEAD (5mm × 7mm) PLASTIC QFN

EXPOSED PAD IS VEE (PIN 39) MUST BE SOLDERED TO PCB

JMAX

= 125°C, θ

= 34°C/W

17 18 19

38 37 36 35 34 33 32

SDAOUT

SDAIN

AD3

AD2

AD1

AD0

DNC

DGND

GATE1

SENSE1

OUT2

GATE2

SENSE2

VEE

OUT3

GATE3

SENSE3

OUT4

GATE4

SCL

INT

MID

RESET

MSD

AUTO

OUT1

VDD

SHDN1

SHDN2

SHDN3

SHDN4

AGND

SENSE4

Supply Voltages (Note 1)

AGND – VEE ........................................... –0.3V to 80V

DGND – VEE ........................................... –0.3V to 80V

VDD – DGND ......................................... –0.3V to 5.5V

Digital Pins

SCL, SDAIN, SDAOUT, INT, SHDNn, MSD, ADn,

RESET, AUTO, MID ........... DGND –0.3V to VDD + 0.3V

Analog Pins

GATEn, SENSEn, OUTn .......... VEE –0.3V to VEE + 80V

Operating Temperature Range

LTC4266C ................................................ 0°C to 70°C

LTC4266I .............................................–40°C to 85°C

Junction Temperature (Note 2) ............................. 125°C

Storage Temperature Range .................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec) ...................300°C

http://www.linear.com/product/LTC4266#orderinfo

LTC4266

4266fg

For more information www.linear.com/LTC4266

electricAl chArActeristics

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Main PoE Supply Voltage AGND – VEE

For IEEE Type 1 Complaint Output

For IEEE Type 2 Complaint Output

Undervoltage Lock-out Level l20 25 30 V

VDD VDD Supply Voltage VDD – DGND l3.0 3.3 4.3 V

Undervoltage Lock-out l2.2 V

Allowable Digital Ground Offset DGND – VEE l25 57 V

IEE VEE Supply Current (AGND – VEE) = 55V l–2.4 –5 mA

IDD VDD Supply Current (VDD – DGND) = 3.3V l1.1 3 mA

Detection

Detection Current – Force Current First Point, AGND – VOUTn = 9V

Second Point, AGND – VOUTn = 3.5V

220

140

240

160

260

180

µA

Detection Voltage – Force Voltage AGND – VOUTn, 5µA ≤ IOUTn ≤ 500µA

First Point

Second Point

Detection Current Compliance AGND – VOUTn = 0V l0.8 0.9 mA

VOC Detection Voltage Compliance AGND – VOUTn, Open Port l10.4 12 V

Detection Voltage Slew Rate AGND – VOUTn, CPORT = 0.15µF l0.01 V/µs

Min. Valid Signature Resistance l15.5 17 18.5 kΩ

Max. Valid Signature Resistance l27.5 29.7 32 kΩ

Classification

VCLASS Classification Voltage AGND – VOUTn, 0mA ≤ ICLASS ≤ 50mA l16.0 20.5 V

Classification Current Compliance VOUTn = AGND l53 61 67 mA

Classification Threshold Current Class 0 – 1

Class 1 – 2

Class 2 – 3

Class 3 – 4

Class 4 – Overcurrent

5.5

13.5

21.5

31.5

45.2

6.5

14.5

7.5

15.5

24.5

34.9

50.8

VMARK Classification Mark State Voltage AGND – VOUTn, 0.1mA ≤ ICLASS ≤ 10mA l7.5 9 10 V

Mark State Current Compliance VOUTn = AGND l53 61 67 mA

Gate Driver

GATE Pin Pull-Down Current Port Off, VGATEn = VEE + 5V

Port Off, VGATEn = VEE + 1V

0.4

0.08

0.12

GATE Pin Fast Pull-Down Current VGATEn = VEE + 5V 30 mA

GATE Pin On Voltage VGATEn – VEE, IGATEn = 1µA l8 12 14 V

Output Voltage Sense

VPG Power Good Threshold Voltage VOUTn – VEE l2 2.4 2.8 V

OUT Pin Pull-Up Resistance to AGND 0V ≤ (AGND – VOUTn) ≤ 5V l300 500 700 kΩ

The l denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C. AGND – VEE = 54V, AGND = DGND, and VDD – DGND = 3.3V unless

otherwise noted. (Notes 3, 4)

LTC4266

4266fg

For more information www.linear.com/LTC4266

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Current Sense

VCUT Overcurrent Sense Voltage VSENSEn – VEE, icut12 = icut34 = hpen = 00h

hpen = 0Fh, cutn[5:0] ≥ 4 (Note 12)

cutrng = 0

cutrng = 1

180

4.5

188

9.38

4.69

196

9.75

4.88

mV/LSB

Overcurrent Sense in AUTO pin mode Class 0, Class 3

Class 1

Class 2

Class 4

152

159

166

VLIM Active Current Limit in 802.3af Compliant

Mode

VSENSEn – VEE, dblpwr = hpen = 00h

VEE = 55V (Note 12)

VEE < VOUT < AGND – 29V

AGND – VOUT = 0V

204

212

220

100

VLIM Active Current Limit in High Power Mode hpen = 0Fh, limn = C0h, VEE = 55V

VOUT – VEE = 0V to 10V

VEE + 23V < VOUT < AGND – 29V

AGND – VOUT = 0V

204

100

212

106

221

113

VLIM Active Current Limit in AUTO pin mode VOUT – VEE = 0V to 10V, VEE = 55V

Class 0 to Class 3

Class 4

102

204

106

212

110

221

VMIN DC Disconnect Sense Voltage VSENSEn – VEE, rdis = 0

VSENSEn – VEE, rdis = 1

2.6

1.3

3.8

1.9

4.8

2.41

VSC Short-Circuit Sense VSENSEn – VEE – VLIM, rdis = 0

VSENSEn – VEE – VLIM, rdis = 1

160

200

100

255

135

Port Current ReadBack

Resolution No missing codes, fast_iv = 0 14 bits

LSB Weight VSENSEn – VEE 30.5 µV/LSB

50-60Hz Noise Rejection (Note 7) 30 dB

Port Voltage ReadBack

Resolution No missing codes, fast_iv = 0 14 bits

LSB Weight AGND – VOUTn 5.835 mV/LSB

50-60Hz noise rejection (Note 7) 30 dB

Digital Interface

VILD Digital Input Low Voltage ADn, SHDNn, RESET, MSD, AUTO,

MID (Note 6)

l0.8 V

I2C Input Low Voltage SCL, SDAIN (Note 6) l0.8 V

VIHD Digital Input High Voltage (Note 6) l2.2 V

Digital Output Low Voltage ISDAOUT = 3mA, IINT = 3mA

ISDAOUT = 5mA, IINT = 5mA

0.4

0.7

Internal Pull-Up to VDD ADn, SHDNn, RESET, MSD 50 kΩ

Internal Pull-Down to DGND AUTO, MID 50 kΩ

electricAl chArActeristics

The l denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C. AGND – VEE = 54V, AGND = DGND, and VDD – DGND = 3.3V unless

otherwise noted. (Notes 3, 4)

LTC4266

4266fg

For more information www.linear.com/LTC4266

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Timing Characteristics

tDET Detection Time Beginning to End of Detection (Note 7) l270 290 310 ms

tDETDLY Detection Delay From PD Connected to Port to Detection

Complete (Note 7)

l300 470 ms

tCLE1 First Class Event Duration (Note 7) l11 12 13 ms

tME1 First Mark Event Duration (Notes 7, 11) l6.8 8.6 10.3 ms

tCLE2 Second Class Event Duration (Note 7) l11 12 13 ms

tME2 Second Mark Event Duration (Note 7) l19 22 ms

tCLE3 Third Class Event Duration CPORT = 0.6µF (Note 7) l0.1 ms

tPON Power On Delay in AUTO pin mode From End of Valid Detect to Application of

Power to Port (Note 7)

l60 ms

Turn On Rise Time (AGND – VOUT): 10% to 90% of

(AGND – VEE), CPORT = 0.15µF (Note 7)

l15 24 µs

Turn On Ramp Rate CPORT = 0.15µF (Note 7) l10 V/µs

Fault Delay From ICUT Fault to Next Detect l1.0 1.1 s

Midspan Mode Detection Backoff Rport = 15.5kΩ (Note 7) l2.3 2.5 2.7 s

Power Removal Detection Delay From Power Removal After tDIS to Next

Detect (Note 7)

l1.0 1.3 2.5 s

tSTART Maximum Current Limit Duration During Port

Start-Up

tSTART1 = 0, tSTART0 = 0 (Notes 7, 12) l52 62.5 66 ms

tLIM Maximum Current Limit Duration After Port

Start-Up

tCUT1 = 0, tCUT0 = 0, tLIM = 0h (Notes 7, 12) l52 62.5 66 ms

tCUT Maximum Overcurrent Duration After Port

Start-Up

tCUT1 = 0, tCUT0 = 0 (Notes 7, 12) l52 62.5 66 ms

Maximum Overcurrent Duty Cycle (Note 7) l5.8 6.3 6.7 %

tMPS Maintain Power Signature (MPS) Pulse Width

Sensitivity

Current Pulse Width to Reset Disconnect

Timer (Notes 7, 8)

l1.6 3.6 ms

tDIS Maintain Power Signature (MPS) Dropout

Time

tconf [1:0] = 00b (Notes 5, 7, 12) l320 350 380 ms

tMSD Masked Shut Down Delay (Note 7) l6.5 µs

tSHDN Port Shut Down Delay (Note 7) l6.5 µs

I2C Watchdog Timer Duration l1.5 2 3 s

Minimum Pulse Width for Masked Shut

Down

(Note 7) l3 µs

Minimum Pulse Width for SHDN (Note 7) l3 µs

Minimum Pulse Width for RESET (Note 7) l4.5 µs

electricAl chArActeristics

The l denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C. AGND – VEE = 54V, AGND = DGND, and VDD – DGND = 3.3V unless

otherwise noted. (Notes 3, 4)

LTC4266

4266fg

For more information www.linear.com/LTC4266

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I2C Timing

Clock Frequency (Note 7) l1 MHz

t1Bus Free Time Figure 5 (Notes 7, 9) l480 ns

t2Start Hold Time Figure 5 (Notes 7, 9) l240 ns

t3SCL Low Time Figure 5 (Notes 7, 9) l480 ns

t4SCL High Time Figure 5 (Notes 7, 9) l240 ns

t5Data Hold Time Figure 5 (Notes 7, 9) Data into chip

Data out of chip

120

t6Data Set-Up Time Figure 5 (Notes 7, 9) l80 ns

t7Start Set-Up Time Figure 5 (Notes 7, 9) l240 ns

t8Stop Set-Up Time Figure 5 (Notes 7, 9) l240 ns

trSCL, SDAIN Rise Time Figure 5 (Notes 7, 9) l120 ns

tfSCL, SDAIN Fall Time Figure 5 (Notes 7, 9) l60 ns

Fault Present to INT Pin Low (Notes 7, 9, 10) l150 ns

Stop Condition to INT Pin Low (Notes 7, 9, 10) l1.5 µs

ARA to INT Pin High Time (Notes 7, 9) l1.5 µs

SCL Fall to ACK Low (Notes 7, 9) l120 ns

Note 1: Stresses beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

Note 2: This IC includes overtemperature protection that is intended

to protect the device during momentary overload conditions. Junction

temperature will exceed 140°C when overtemperature protection is active.

Continuous operation above the specified maximum operating junction

temperature may impair device reliability.

Note 3: All currents into device pins are positive; all currents out of device

pins are negative.

Note 4: The LTC4266 operates with a negative supply voltage (with

respect to ground). To avoid confusion, voltages in this data sheet are

referred to in terms of absolute magnitude.

Note 5: tDIS is the same as tMPDO defined by IEEE 802.3at.

Note 6: The LTC4266 digital interface operates with respect to DGND. All

logic levels are measured with respect to DGND.

Note 7: Guaranteed by design, not subject to test.

Note 8: The IEEE 802.3af specification allows a PD to present its

Maintain Power Signature (MPS) on an intermittent basis without being

disconnected. In order to stay powered, the PD must present the MPS for

tMPS within any tMPDO time window.

Note 9: Values measured at VILD(MAX) and VIHD(MIN).

Note 10: If fault condition occurs during an I2C transaction, the INT pin

will not be pulled down until a stop condition is present on the I2C bus.

Note 11: Load Characteristic of the LTC4266 during Mark:

7V < (AGND – VOUTn) < 10V or IOUT < 50µA

Note 12: See the LTC4266 Software Programming documentation for

information on serial bus usage and device configuration and status

registers.

electricAl chArActeristics

The l denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C. AGND – VEE = 54V, AGND = DGND, and VDD – DGND = 3.3V unless

otherwise noted. (Notes 3, 4)

LTC4266

4266fg

For more information www.linear.com/LTC4266

typicAl perForMAnce chArActeristics

Power On Sequence

in AUTO Pin Mode Powering Up into a 180µF Load

802.3af Classification

in AUTO Pin Mode

2-Event Classification

in Auto Pin Mode

Classification Transient Response

to 40mA Load Step Classification Current Compliance

VDD Supply Current vs Voltage

100ms/DIV

–70

–60

PORT VOLTAGE (V)

–10

–20

–30

–40

–50

4266 G01

PORT 1

VDD = 3.3V

VEE = –54V

FORCED CURRENT DETECTION

FORCED VOLTAGE

DETECTION

802.3af

CLASSIFICATION

POWER ON

GND

VEE

5ms/DIV

GND

0mA

4266 G02

VEE

GATE

VOLTAGE

10V/DIV

PORT

CURRENT

200 mA/DIV

PORT

VOLTAGE

20V/DIV

FOLDBACK

FET ON

425mA

CURRENT LIMIT

LOAD

FULLY

CHARGED

VDD = 3.3V

VEE = –54V

5ms/DIV

VEE

–18.4

PORT

VOLTAGE

10V/DIV

GND

4266 G03

PORT 1

VDD = 3.3V

VEE = –55V

PD IS CLASS 1

10ms/DIV

VEE

–17.6

PORT

VOLTAGE

10V/DIV

GND

4266 G04

PORT 1

VDD = 3.3V

VEE = –55V

PD IS CLASS 4

1ST CLASS EVENT

2ND CLASS EVENT

50µs/DIV

40mA

0mA

4266 G05

–20V

PORT

VOLTAGE

1V/DIV

PORT

CURRENT

20mA/DIV

VDD = 3.3V

VEE = –54V

VDD SUPPLY VOLTAGE (V)

2.7

0.8

IDD SUPPLY CURRENT (mA)

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

2.9 3.1 3.3 3.5

4266 G07

3.7 3.9 4.1 4.3

–40°C

25°C

85°C

VEE Supply Current vs Voltage

802.3at ILIM Threshold vs

Temperature

VEE SUPPLY VOLTAGE (V)

–60

2.0

IEE SUPPLY CURRENT (mA)

2.1

2.2

2.3

2.4

–55 –50 –45 –40

4266 G08

–35 –30 –25 –20

–40°C

25°C

85°C

TEMPERATURE (°C)

–40

210

LIM

(mV)

ILIM (mA)

211

213

212

214

215

840

844

852

848

856

860

0 40

4266 G09

–80 120

VDD = 3.3V

VEE = –54V

RSENSE = 0.25Ω

REG 48h = C0h

CLASSIFICATION CURRENT (mA)

–20

CLASSIFICATION VOLTAGE (V)

–18

–16

–14

–12

–10

–8

–6

–4

–2

0 10 20 30

4266 G06

40 50 60 70

VDD = 3.3V

VEE = –54V

TA = 25°C

LTC4266

4266fg

For more information www.linear.com/LTC4266

typicAl perForMAnce chArActeristics

802.3af ILIM Threshold vs

Temperature

DC Disconnect Threshold vs

Temperature

Current Limit Foldback

ADC Noise Histogram

Current Readback in Fast Mode

ADC Integral Nonlinearity

Current Readback in Fast Mode

TEMPERATURE (°C)

–40

105.00

VLIM (mV)

LIM

(mA)

106.50

105.75

107.25

108.00

420

423

426

429

432

0 40

4266 G10

80 120

VDD = 3.3V

VEE = –54V

RSENSE = 0.25Ω

REG 48h = 80h

PORT 1

802.3at ICUT Threshold vs

Temperature

802.3af ICUT Threshold vs

Temperature

TEMPERATURE (°C)

–40

158

VCUT (mV)

CUT

(mA)

161

160

159

162

163

630

636

640

648

644

652

0 40

4266 G11

80 120

VDD = 3.3V

VEE = –54V

RSENSE = 0.25Ω

REG 47h = E2h

PORT 1

TEMPERATURE (°C)

–40

93.00

VCUT (mV)

CUT

(mA)

94.50

93.75

95.25

96.00

372

375

378

381

384

0 40

4266 G12

80 120

VDD = 3.3V

VEE = –54V

RSENSE = 0.25Ω

REG 47h = D4h

PORT 1

TEMPERATURE (°C)

–40

MIN

(mV)

IMIN (mV)

7.00

7.50

7.25

7.75

8.00

1.7500

1.8125

1.8750

1.9375

2.0000

0 40

4266 G13

80 120

VDD = 3.3V

VEE = –54V

RSENSE = 0.25Ω

REG 47h = E2h

PORT 1

VOUTn (V)

–54

LIM

(mA)

VLIM (mV)

900

800

700

600

500

400

300

200

100

225

200

175

150

125

100

–36–45 –27

4266 G14

–18 –9 0

VDD = 3.3V

VEE = –54V

RSENSE = 0.25Ω

REG 48h = C0h

ADC OUTPUT

191

COUNT

400

350

300

250

200

150

100

193192 194

4266 G15

195 196

VSENSEn – VEE = 110.4mV

CURRENT SENSE RESISTOR INPUT VOLTAGE (mV)

ADC INTEGRAL NONLINEARITY (LSBs)

0.5

400

4266 G16

–0.5

–1.0 100 200 250 500

1.0

300

50 150 450

350

LTC4266

4266fg

For more information www.linear.com/LTC4266

typicAl perForMAnce chArActeristics

ADC Noise Histogram

Current Readback in Slow Mode

ADC Integral Nonlinearity

Current Readback in Slow Mode

ADC Noise Histogram Port

Voltage Readback in Fast Mode

ADC Integral Nonlinearity

Voltage Readback in Fast Mode

ADC Noise Histogram Port

Voltage Readback in Slow Mode

ADC Integral Nonlinearity

Voltage Readback in Slow Mode

INT and SDAOUT Pull Down

Voltage vs Load Current

MOSFET Gate Drive With Fast

Pull Down

ADC OUTPUT

BIN COUNT

300

250

200

150

100

6139 6141

4266 G17

6143 6145 6147

VSENSEn – VEE = 110.4mV

ADC OUTPUT

260

BIN COUNT

600

500

400

300

200

100

262261 263

4266 G19

264 265

AGND – VOUTn = 48.3V

ADC OUTPUT

8532

BIN COUNT

600

500

400

300

200

100

85348533 8535

4266 G21

8536

AGND – VOUTn = 48.3V

LOAD CURRENT (mA)

PULL DOWN VOLTAGE (V)

2.5

1.5

0.5

10515

4266 G23

20 25 30 35 40 100µs/DIV

GND

0mA

4266 G24

VEE

PORT

CURRENT

500mA/DIV

GATE

VOLTAGE

10V/DIV

PORT

VOLTAGE

20V/DIV

CURRENT LIMIT

50Ω FAULT REMOVED

50Ω

FAULT

APPLIED

VDD = 3.3V

VEE = –54V

FAST PULL DOWN

CURRENT SENSE RESISTOR INPUT VOLTAGE (mV)

ADC INTEGRAL NONLINEARITY (LSBs)

0.5

400

4266 G18

–0.5

–1.0 100 200 250 500

1.0

300

50 150 450

350

PORT VOLTAGE (V)

ADC INTEGRAL NONLINEARITY (LSBs)

0.5

4266 G20

–0.5

–1.0 20 30 60

1.0

PORT VOLTAGE (V)

ADC INTEGRAL NONLINEARITY (LSBs)

0.5

4266 G22

–0.5

–1.0 20 30 60

1.0

LTC4266

4266fg

For more information www.linear.com/LTC4266

test tiMing DiAgrAMs

Figure 1. Detect, Class and Turn-On Timing in AUTO Pin or Semi-Auto Modes

Figure 2. Current Limit Timing Figure 3. DC Disconnect Timing

Figure 4. Shut Down Delay Timing Figure 5. I2C Interface Timing

VLIM VCUT

VSENSEn TO VEE

INT

4266 F02

tSTART, tICUT

SCL

SDA

t3tr

t5t6t7t8

4266 F05

VMIN

VSENSEn

TO VEE

INT

tDIS

tMPS 4266 F03

VPORTn

INT

tDETDLY

VOC

VEE

tDET

tME1

tME2

VMARK

VCLASS

15.5V

20.5V

tCLE1

tCLE2

tCLE3

CONNECTED

4266 F01

FORCED-CURRENT

CLASSIFICATION

tPON

FORCED-

VOLTAGE

VGATEn

VEE

MSD or

SHDNn

tSHDN

tMSD

4266 F04

LTC4266

4266fg

For more information www.linear.com/LTC4266

i2c tiMing DiAgrAMs

Figure 6. Writing to a Register

Figure 7. Reading from a Register

SCL

SDA

4266 F06

0 01 AD3 AD2 AD1 AD0 A7 A6 A5 A4 A3 A2 A1 A0

R/W ACK D7 D6 D5 D4 D3 D2 D1 D0

ACK ACK

START BY

MASTER

ACK BY

SLAVE

ACK BY

SLAVE

ACK BY

SLAVE

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

FRAME 3

DATA BYTE

STOP BY

MASTER

SCL

SDA 0 01 AD3 AD2 AD1 AD0 A7 A6 A5 A4 A3 A2 A1 A0

R/W ACK ACK 0 01 AD3 AD2 AD1 AD0 D7 D6 D5 D4 D3 D2 D1 D0

R/W ACK ACK

START BY

MASTER

ACK BY

SLAVE

ACK BY

SLAVE

4266 F07

STOP BY

MASTER

REPEATED

START BY

MASTER

ACK BY

SLAVE

NO ACK BY

MASTER

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

DATA BYTE

Figure 8. Reading the Interrupt Register (Short Form)

Figure 9. Reading from Alert Response Address

SCL

SDA

4266 F08

0 1 0AD3 AD2 AD1 AD0 D7 D6 D5 D4 D3 D2 D1 D0

R/W ACK ACK

START BY

MASTER

ACK BY

SLAVE

NO ACK BY

MASTER

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

DATA BYTE

STOP BY

MASTER

SCL

SDA

4266 F09

0 0 110AD30000 1 AD2 AD1 AD0

R/W ACK ACK1

START BY

MASTER

ACK BY

SLAVE

NO ACK BY

MASTER

FRAME 1

ALERT RESPONSE ADDRESS BYTE

FRAME 2

SERIAL BUS ADDRESS BYTE

STOP BY

MASTER

LTC4266

4266fg

For more information www.linear.com/LTC4266

pin Functions

RESET: Chip Reset, Active Low. When the RESET pin is

low, the LTC4266 is held inactive with all ports off and

all internal registers reset to their power-up states. When

RESET is pulled high, the LTC4266 begins normal opera-

tion. RESET can be connected to an external capacitor or

RC network to provide a power turn-on delay. Internal

filtering of the RESET pin prevents glitches less than 1µs

wide from resetting the LTC4266. Internally pulled up to

VDD.

MID: Midspan Mode Input. When high, the LTC4266 acts

as a midspan device. Internally pulled down to DGND.

INT: Interrupt Output, Open Drain. INT will pull low when

any one of several events occur in the LTC4266. It will

return to a high impedance state when bits 6 or 7 are set

in the Reset PB register (1Ah). The INT signal can be used

to generate an interrupt to the host processor, eliminating

the need for continuous software polling. Individual INT

events can be disabled using the Int Mask register (01h).

See LTC4266 Software Programming documentation for

more information. The INT pin is only updated between

I2C transactions.

SCL: Serial Clock Input. High impedance clock input for

the I2C serial interface bus. SCL must be tied high if not

used.

SDAOUT: Serial Data Output, Open Drain Data Output for

the I2C Serial Interface Bus. The LTC4266 uses two pins

to implement the bidirectional SDA function to simplify

opto-isolation of the I2C bus. To implement a standard

bidirectional SDA pin, tie SDAOUT and SDAIN together.

SDAOUT should be grounded or left floating if not used.

See Applications Information for more information.

SDAIN: Serial Data Input. High impedance data input for

the I2C serial interface bus. The LTC4266 uses two pins

to implement the bidirectional SDA function to simplify

opto-isolation of the I2C bus. To implement a standard

bidirectional SDA pin, tie SDAOUT and SDAIN together.

SDAIN must be tied high if not used. See Applications

Information for more information.

AD3: Address Bit 3. Tie the address pins high or low to

set the I

C serial address to which the LTC4266 responds.

This address will be 010A3A2A1A0b. Internally pulled up

to VDD.

AD2: Address Bit 2. See AD3.

AD1: Address Bit 1. See AD3.

AD0: Address Bit 0. See AD3.

NC, DNC: All pins identified with “NC” or “DNC” must be

left unconnected.

DGND: Digital Ground. DGND is the return for the V

supply.

VDD: Logic Power Supply. Connect to a 3.3V power supply

relative to DGND. VDD must be bypassed to DGND near

the LTC4266 with at least a 0.1µF capacitor.

SHDN1: Shutdown Port 1, Active Low. When pulled low,

SHDN1 shuts down port 1, regardless of the state of

the internal registers. Pulling SHDN1 low is equivalent

to setting the Reset Port 1 bit in the Reset Pushbutton

vents glitches less than 1µs wide from resetting the port.

Internally pulled up to VDD.

SHDN2: Shutdown Port 2, Active Low. See SHDN1.

SHDN3: Shutdown Port 3, Active Low. See SHDN1.

SHDN4: Shutdown Port 4, Active Low. See SHDN1.

AGND: Analog Ground. AGND is the return for the VEE

supply.

SENSE4: Port 4 Current Sense Input. SENSE4 monitors

the external MOSFET current via a 0.5Ω or 0.25Ω sense

resistor between SENSE4 and VEE. Whenever the voltage

across the sense resistor exceeds the overcurrent detec-

tion threshold VCUT, the current limit fault timer counts

up. If the voltage across the sense resistor reaches the

current limit threshold VLIM, the GATE4 pin voltage is low-

ered to maintain constant current in the external MOSFET.

See Applications Information for further details. If the port

is unused, the SENSE4 pin must be tied to VEE.

LTC4266

4266fg

For more information www.linear.com/LTC4266

pin Functions

GATE4: Port 4 Gate Drive. GATE4 should be connected

to the gate of the external MOSFET for port 4. When the

MOSFET is turned on, the gate voltage is driven to 12V

(typ) above VEE. During a current limit condition, the

voltage at GATE4 will be reduced to maintain constant

current through the external MOSFET. If the fault timer

expires, GATE4 is pulled down, turning the MOSFET off

and recording a tCUT or tSTART event. If the port is unused,

float the GATE4 pin.

OUT4: Port 4 Output Voltage Monitor. OUT4 should be

connected to the output port. A current limit foldback

circuit limits the power dissipation in the external MOSFET

by reducing the current limit threshold when the drain-to-

source voltage exceeds 10V. The port 4 Power Good bit is

set when the voltage from OUT4 to VEE drops below 2.4V

(typ). A 500k resistor is connected internally from OUT4

to AGND when the port is idle. If the port is unused, OUT4

pin must be floated.

SENSE3: Port 3 Current Sense Input. See SENSE4.

GATE3: Port 3 Gate Drive. See GATE4.

OUT3: Port 3 Output Voltage Monitor. See OUT4.

VEE: Main Supply Input. Connect to a –45V to –57V

supply, relative to AGND.

SENSE2: Port 2 Current Sense Input. See SENSE4.

GATE2: Port 2 Gate Drive. See GATE4.

OUT2: Port 2 Output Voltage Monitor. See OUT4.

SENSE1: Port 1 Current Sense Input. See SENSE4.

GATE1: Port 1 Gate Drive. See GATE 4.

OUT1: Port 1 Output Voltage Monitor. See OUT4.

AUTO: AUTO Pin Mode Input. AUTO pin mode allows the

LTC4266 to detect and power up a PD even if there is no

host controller present on the I2C bus. The voltage of the

AUTO pin determines the state of the internal registers

when the LTC4266 is reset or comes out of VDD UVLO

(see the Register map). The states of these register bits

can subsequently be changed via the I2C interface. The

real-time state of the AUTO pin is read at bit 0 in the Pin

Status register (11h). Internally pulled down to DGND.

Must be tied locally to either VDD or DGND.

MSD: Maskable Shutdown Input. Active low. When pulled

low, all ports that have their corresponding mask bit set

in the Misc Config register (17h) will be reset, equivalent

to pulling the SHDN pin low. Internal filtering of the MSD

pin prevents glitches less than 1µs wide from resetting

ports. Internally pulled up to VDD.

LTC4266

4266fg

For more information www.linear.com/LTC4266

operAtion

Figure 10. Power Over Ethernet System Diagram

Overview

Power over Ethernet, or PoE, is a standard protocol for

sending DC power over copper Ethernet data wiring.

The IEEE group that administers the 802.3 Ethernet data

standards added PoE powering capability in 2003. This

original PoE spec, known as 802.3af, allowed for 48V DC

power at up to 13W. This initial spec was widely popular,

but 13W was not adequate for some requirements. In

2009, the IEEE released a new standard, known as 802.3at

or PoE+, increasing the voltage and current requirements

to provide 25W of power.

The IEEE standard also defines PoE terminology. A device

that provides power to the network is known as a PSE,

or power sourcing equipment, while a device that draws

power from the network is known as a PD, or powered

device. PSEs come in two types: Endpoints (typically net-

work switches or routers), which provide data and power;

and Midspans, which provide power but pass through

data. Midspans are typically used to add PoE capabil-

ity to existing non-PoE networks. PDs are typically IP

phones, wireless access points, security cameras, and

similar devices, but could be nearly anything that runs

from 25W or less and includes an RJ45-style network

connector.

The LTC4266 is a third-generation quad PSE controller

that implements four PSE ports in either an endpoint

or midspan design. Virtually all necessary circuitry is

included to implement a IEEE 802.3at compliant PSE

design, requiring only an external power MOSFET and

sense resistor per channel; these minimize power loss

compared to alternative designs with on-board MOSFETs

and increase system reliability in the event a single chan-

nel is damaged.

PoE Basics

Common Ethernet data connections consist of two or four

twisted pairs of copper wire (commonly known as CAT-5

cable), transformer-coupled at each end to avoid ground

loops. PoE systems take advantage of this coupling

arrangement by applying voltage between the center-taps

of the data transformers to transmit power from the PSE

to the PD without affecting data transmission. Figure 10

shows a high-level PoE system schematic.

To avoid damaging legacy data equipment that does not

expect to see DC voltage, the PoE spec defines a proto-

col that determines when the PSE may apply and remove

power. Valid PDs are required to have a specific 25k com-

mon-mode resistance at their input. When such a PD is

connected to the cable, the PSE detects this signature

resistance and turns on the power. When the PD is later

4266 F10

DATA PAIR

VEE GATE

SPARE PAIR

1/4

LTC4266

AGND

I2C

–54V

CAT 5

20Ω MAX

ROUNDTRIP

0.05µF MAX

RJ45

PSE PD

PWRGD

–54VOUT

LTC4265

GND

DC/DC

CONVERTER +

–

VOUT

GND

–54VIN

LTC4266

4266fg

For more information www.linear.com/LTC4266

operAtion

disconnected, the PSE senses the open circuit and turns

power off. The PSE also turns off power in the event of a

current fault or short circuit.

When a PD is detected, the PSE optionally looks for a

classification signature that tells the PSE the maximum

power the PD will draw. The PSE can use this information

to allocate power among several ports, police the current

consumption of the PD, or to reject a PD that will draw

more power that the PSE has available. The classification

step is optional; if a PSE chooses not to classify a PD, it

must assume that the PD is a 13W (full 802.3af power)

device.

New in 802.3at

The newer 802.3at standard supersedes 802.3af and

brings several new features:

• A PD may draw as much as 25.5W. Such PDs (and

the PSEs that support them) are known as Type 2.

Older 13W 802.3af equipment is classified as Type 1.

Type 1 PDs will work with all PSEs; Type 2 PDs may

require Type 2 PSEs to work properly. The LTC4266

is designed to work in both Type 1 and Type 2 PSE

designs, and also supports non-standard configura-

tions at higher power levels.

• The Classification protocol is expanded to allow Type

2 PSEs to detect Type 2 PDs, and to allow Type 2 PDs

to determine if they are connected to a Type 2 PSE.

Two versions of the new Classification protocol are

available: an expanded version of the 802.3af Class

Pulse protocol, and an alternate method integrated

with the existing LLDP protocol (using the Ethernet

data path). The LTC4266 fully supports the new Class

Pulse protocol and is also compatible with the LLDP

protocol (which is implemented in the data commu-

nications layer, not in the PoE circuitry).

• Fault protection current levels and timing are adjusted

to reduce peak power in the MOSFET during a fault;

this allows the new 25.5W power levels to be reached

using the same MOSFETs as older 13W designs.

BACKWARDS COMPATIBILITY

The LTC4266 is designed to be backward compatible

with earlier PSE chips in both software and pin functions.

Existing systems using either the LTC4258 or LTC4259A

(or compatible) devices can be substituted with the

LTC4266 without software or PCB layout changes; only

minor BOM changes are required to implement a fully

compliant 802.3at design.

Because of the backwards compatibility features, some of

the internal registers are redundant or unused when the

LTC4266 is operated as recommended. For more details

on usage in compatibility mode, refer to the LTC4258/

LTC4259A device data sheets.

Special Compatibility Mode Notes

• The LTC4266 can use either 0.5Ω or 0.25Ω sense

resistors, while the LTC425x chips always used 0.5Ω.

To maintain compatibility, if the AUTO pin is low when

the LTC4266 powers up it assumes the sense resis-

tor is 0.5Ω; if it is high at power up, the LTC4266

assumes 0.25Ω. The resistor value setting can be

reconfigured at any time after power up. In particu-

lar, systems that use 0.25Ω sense resistors and have

AUTO tied low must reconfigure the resistor settings

after power up.

• The LTC4259A included both AC and DC disconnect

sensing circuitry, but the LTC4266 has only DC dis-

connect sensing. For the sake of compatibility, regis-

ter bits used to enable AC disconnect in the LTC4259A

are implemented in the LTC4266, but they simply mir-

ror the bits used for DC disconnect.

• The LTC4258 and LTC4259A required 10k resis-

tors between the OUTn pins and the drains of the

external MOSFETs. These resistors must be shorted

or replaced with zero ohm jumpers when using the

LTC4266.

• The LTC4258 and LTC4259A included a BYP pin,

decoupled to AGND with 0.1µF. This pin changes to

the MID pin on the LTC4266. The capacitor should be

removed for Endspan applications, or replaced with a

zero ohm jumper for Midspan applications.

LTC4266

4266fg

For more information www.linear.com/LTC4266

ApplicAtions inForMAtion

Operating Modes

The LTC4266 includes four independent ports, each of

which can operate in one of four modes: manual, semi-

auto, AUTO pin or shutdown.

Table 1. Operating Modes

MODE

AUTO

PIN OPMD

DETECT/

CLASS POWER-UP

AUTOMATIC

ICUT/ILIM

ASSIGNMENT

AUTO Pin 1 11b Enabled at

Reset

Automatically

Yes

Reserved 0 11b N/A N/A N/A

Semi-auto 0 10b Host

Enabled

Upon

Request

Manual 0 01b Once Upon

Request

Upon

Request

Shutdown 0 00b Disabled Disabled No

• In manual mode, the port waits for instructions from

the host system before taking any action. It runs a

single detection or classification cycle when com-

manded to by the host, and reports the result in its

Port Status register. The host system can command

the port to turn on or off the power at any time. This

mode should only be used for diagnostic and test

purposes.

• In semi-auto mode, the port repeatedly attempts to

detect and classify any PD attached to it. It reports

the status of these attempts back to the host, and

waits for a command from the host before turning

on power to the port. The host must enable detec-

tion (and optionally classification) for the port before

detection will start.

• AUTO pin mode operates the same as semi-auto

mode except that it will automatically turn on the

power to the port if detection is successful. In AUTO

pin mode, ICUT and ILIM values are set automatically

by the LTC4266. This operational mode is only valid if

the AUTO pin is high at reset or power-up and remains

high during operation.

• In shutdown mode, the port is disabled and will not

detect or power a PD.

Regardless of which mode it is in, the LTC4266 will

remove power automatically from any port that gener

ates a current limit fault. It will also automatically remove

power from any port that generates a disconnect event if

disconnect detection is enabled. The host controller may

also command the port to remove power at any time.

Reset and the AUTO/MID Pins

The initial LTC4266 configuration depends on the state

of the AUTO and MID pins during reset. Reset occurs at

power-up, or whenever the RESET pin is pulled low or

the global Reset All bit is set. Changing the state of AUTO

or MID after power-up will not properly change the port

behavior of the LTC4266 until a reset occurs.

Although typically used with a host controller, the LTC4266

can also be used in a standalone mode with no connec-

tion to the serial interface. If there is no host present, the

AUTO pin must be tied high so that, at reset, all ports

will be configured to operate automatically. Each port will

detect and classify repeatedly until a PD is discovered,

set ICUT and ILIM according to the classification results,

apply power after successful detection, and remove power

when a PD is disconnected. Similarly, if the standalone

application is a midspan, the MID pin must be tied high

to enable correct midspan detection timing.

Table 2 shows the ICUT and ILIM values that will be auto-

matically set in AUTO pin mode, based on the discovered

class.

Table 2. ICUT and ILIM Values in AUTO pin mode

CLASS ICUT ILIM

Class 1 112mA 425mA

Class 2 206mA 425mA

Class 3 or Class 0 375mA 425mA

Class 4 638mA 850mA

The automatic setting of the ICUT and ILIM values only

occurs if the LTC4266 is reset with the AUTO pin high.

LTC4266

4266fg

For more information www.linear.com/LTC4266

RESISTANCE

PSE

0Ω 10k

15k

4266 F11

19k 26.5k

26.25k23.75k

150Ω (NIC)

20k 30k

33k

Figure 11. IEEE 802.3af Signature Resistance Ranges

ApplicAtions inForMAtion

DETECTION

Detection Overview

To avoid damaging network devices that were not

designed to tolerate DC voltage, a PSE must determine

whether the connected device is a real PD before apply-

ing power. The IEEE specification requires that a valid PD

have a common-mode resistance of 25k ±5% at any port

voltage below 10V. The PSE must accept resistances that

fall between 19k and 26.5k, and it must reject resistances

above 33k or below 15k (shaded regions in Figure 11).

The PSE may choose to accept or reject resistances in

the undefined areas between the must-accept and must-

reject ranges. In particular, the PSE must reject standard

computer network ports, many of which have 150Ω com-

mon-mode termination resistors that will be damaged if

power is applied to them (the black region at the left of

Figure 11).

first forced-current test, the detection cycle will abort and

Short Circuit will be reported. Table 3 shows the possible

detection results.

Table 3. Detection Status

MEASURED PD SIGNATURE DETECTION RESULT

Incomplete or Not Yet Tested Detect Status Unknown

<2.4k Short Circuit

Capacitance > 2.7µF CPD too High

2.4k < RPD < 17k RSIG too Low

17k < RPD < 29k Detect Good

>29k RSIG too High

>50k Open Circuit

Voltage > 10V Port Voltage Outside Detect Range

Operating Modes

The port’s operating mode determines when the LTC4266

runs a detection cycle. In manual mode, the port will

idle until the host orders a detect cycle. It will then run

detection, report the results, and return to idle to wait for

another command.

In semi-auto mode, the LTC4266 autonomously polls a

port for PDs, but it will not apply power until commanded

to do so by the host. The Port Status register is updated

at the end of each detection cycle. If a valid signature

resistance is detected and classification is enabled, the

port will classify the PD and report that result as well.

The port will then wait for at least 100ms (or 2 seconds if

midspan mode is enabled), and will repeat the detection

cycle to ensure that the data in the port status register is

up-to-date.

Figure 12. PD Detection

FIRST

DETECTION

POINT

SECOND

DETECTION

POINT

VALID PD

25kΩ SLOPE

275

165

CURRENT (µA)

0V-2V

OFFSET VOLTAGE

4266 F12

4-Point Detection

The LTC4266 uses a 4-point detection method to dis-

cover PDs. False-positive detections are minimized by

checking for signature resistance with both forced-current

and forced-voltage measurements. Initially, two test cur-

rents are forced onto the port (via the OUTn pin) and the

resulting voltages are measured. The detection circuitry

subtracts the two V-I points to determine the resistive

slope while removing offset caused by series diodes or

leakage at the port (see Figure 12). If the forced-current

detection yields a valid signature resistance, two test

voltages are then forced onto the port and the resulting

currents are measured and subtracted. Both methods

must report valid resistances for the port to report a valid

detection. PD signature resistances between 17k and 29k

(typically) are detected as valid and reported as Detect

Good in the corresponding Port Status register. Values

outside this range, including open and short circuits, are

also reported. If the port measures less than 1V at the

LTC4266

4266fg

For more information www.linear.com/LTC4266

ApplicAtions inForMAtion

If the port is in semi-auto mode and high power opera-

tion is enabled, the port will not turn on in response to

a power-on command unless the current detect result is

Detect Good. Any other detect result will generate a tSTART

fault if a power-on command is received. If the port is not

in high power mode, it will ignore the detection result and

apply power when commanded, maintaining backwards

compatibility with the LTC4259A.

Behavior in AUTO pin mode is similar to semi-auto;

however, after Detect Good is reported and the port is

classified (if classification is enabled), it is automatically

powered on without further intervention. In AUTO pin

mode, the ICUT and ILIM thresholds are automatically set;

see the Reset and the AUTO/MID Pins section for more

information.

The signature detection circuitry is disabled when the port

is initially powered up with the AUTO pin low, in shutdown

mode, or when the corresponding detect enable bit is

cleared.

Detection of Legacy PDs

Proprietary PDs that predate the original IEEE 802.3af

standard are commonly referred to today as legacy

devices. One type of legacy PD uses a large common-

mode capacitance (>10μF) as the detection signature.

Note that PDs in this range of capacitance are defined as

invalid, so a PSE that detects legacy PDs is technically

noncompliant with the IEEE spec.

The LTC4266 can be configured to detect this type of

legacy PD. Legacy detection is disabled by default, but can

be manually enabled on a per-port basis. When enabled,

the port will report detect good when it sees either a valid

IEEE PD or a high-capacitance legacy PD. With legacy

mode disabled, only valid IEEE PDs will be recognized.

CLASSIFICATION

802.3af Classification

A PD can optionally present a classification signature to

the PSE to indicate the maximum power it will draw while

operating. The IEEE specification defines this signature

as a constant current draw when the PSE port voltage

is in the VCLASS range (between 15.5V and 20.5V), with

the current level indicating one of 5 possible PD classes.

Figure 13 shows a typical PD load line, starting with the

slope of the 25kΩ signature resistor below 10V, then tran-

sitioning to the classification signature current (in this

case, Class3) in the VCLASS range. Table 4 shows the

possible classification values.

Table 4. Classification Values

CLASS RESULT

Class 0 No Class Signature Present; Treat Like Class 3

Class 1 3W

Class 2 7W

Class 3 13W

Class 4 25.5W (Type 2)

If classification is enabled, the port will classify the PD

immediately after a successful detection cycle in semi-

auto or AUTO pin modes, or when commanded to in man-

ual mode. It measures the PD classification signature by

applying 18V for 12ms (both values typical) to the port via

the OUTn pin and measuring the resulting current; it then

reports the discovered class in the port status register. If

the LTC4266 is in AUTO pin mode, it will additionally use

the classification result to set the I

CUT

and I

LIM

thresholds.

See the Reset and the AUTO/MID Pins section for more

information.

The classification circuitry is disabled when the port is

initially powered up with the AUTO pin low, in shutdown

mode, or when the corresponding class enable bit is

cleared.

VOLTAGE (VCLASS)

CURRENT (mA)

05 10 15 20

4266 F13

TYPICAL

CLASS 3

PD LOAD

LINE

48mA

33mA

PSE LOAD LINE

23mA

14.5mA

6.5mA

CLASS 4

CLASS 2

CLASS 1

CLASS 0

CLASS 3

OVER

CURRENT

Figure 13. PD Classification

LTC4266

4266fg

For more information www.linear.com/LTC4266

ApplicAtions inForMAtion

802.3at 2-Event Classification

The 802.3at spec defines two methods of classifying a

Type 2 PD.

One method adds extra fields to the Ethernet LLDP data

protocol; although the LTC4266 is compatible with this

classification method, it cannot perform classification

directly since it doesn’t have access to the data path.

LLDP classification requires the PSE to power the PD as

a standard 802.3af (Type 1) device. It then waits for the

host to perform LLDP communication with the PD and

update the PSE port data. The LTC4266 supports chang-

ing the ILIM and ICUT levels on the fly, allowing the host

to complete LLDP classification.

The second 802.3at classification method, known as

2-event classification or ping-pong, is fully supported by

the LTC4266. A Type 2 PD that is requesting more than

13W will indicate Class 4 during normal 802.3af classifi-

cation. If the LTC4266 sees Class 4, it forces the port to

a specified lower voltage (called the mark voltage, typi-

cally 9V), pauses briefly, and then re-runs classification

to verify the Class 4 reading (Figure 1). It also sets a bit in

the High Power Status register to indicate that it ran the

second classification cycle. The second cycle alerts the

PD that it is connected to a Type 2 PSE which can supply

Type 2 power levels.

2-event ping-pong classification is enabled by setting a

bit in the port’s High Power Mode register. Note that a

ping-pong enabled port only runs the second classifica-

tion cycle when it detects a Class 4 device; if the first cycle

returns Class 0 to 3, the port assumes it is connected to

a Type 1 PD and does not run the second classification

cycle.

Invalid Type 2 Class Combinations

The 802.3at spec defines a Type 2 PD class signature as

two consecutive Class 4 results; a Class 4 followed by a

Class 0-3 is not a valid signature. In AUTO pin mode, the

LTC4266 will power a detected PD regardless of the clas-

sification results, with one exception: if the PD presents

an invalid Type 2 signature (Class 4 followed by Class 0

to 3), the LTC4266 will not provide power and will restart

the detection process. To aid in diagnosis, the Port Status

pulse, so an invalid Class 4–Class 2 combination would

report a second class pulse was run in the High Power

Status register (which implies that the first cycle found

Class 4), and Class 2 in the Port Status register.

POWER CONTROL

External MOSFET, Sense R Summary

The primary function of the LTC4266 is to control the

delivery of power to the PSE port. It does this by control-

ling the gate drive voltage of an external power MOSFET

while monitoring the current via an external sense resis-

tor and the output voltage at the OUT pin. This circuitry

serves to couple the raw VEE input supply to the port in

a controlled manner that satisfies the PD’s power needs

while minimizing power dissipation in the MOSFET and

disturbances on the VEE backplane.

The LTC4266 is designed to use 0.25Ω sense resistors to

minimize power dissipation. It also supports 0.5Ω sense

resistors, which are the default when LTC4258/LTC4259A

compatibility is desired.

Inrush Control

Once the command has been given to turn on a port, the

LTC4266 ramps up the GATE pin of that port’s external

MOSFET in a controlled manner. Under normal power-up

circumstances, the MOSFET gate will rise until the port

current reaches the inrush current limit level (typically

450mA), at which point the GATE pin will be servoed to

maintain the specified IINRUSH current. During this inrush

period, a timer (t

START

) runs. When output charging is

complete, the port current will fall and the GATE pin will

be allowed to continue rising to fully enhance the MOSFET

and minimize its on-resistance. The final V

is nominally

12V. If the tSTART timer expires before the inrush period

completes, the port will be turned back off and a tSTART

fault reported.

Current Limit

Each LTC4266 port includes two current limiting thresh-

olds (ICUT and ILIM), each with a corresponding timer (tCUT

and tLIM). Setting the ICUT and ILIM thresholds depends

LTC4266

4266fg

For more information www.linear.com/LTC4266

ApplicAtions inForMAtion

on several factors: the class of the PD, the voltage of the

main supply (V

), the type of PSE (1 or 2), the sense

resistor (0.5Ω or 0.25Ω), the SOA of the MOSFET, and

whether or not the system is required to implement class

enforcement.

Per the IEEE spec, the LTC4266 will allow the port cur-

rent to exceed ICUT for a limited period of time before

removing power from the port, whereas it will actively

control the MOSFET gate drive to keep the port current

below ILIM. The port does not take any action to limit the

current when only the ICUT threshold is exceeded, but

does start the tCUT timer. The tLIM timer starts when the

ILIM threshold is exceeded and current limit is active. If

the current drops below the ICUT current threshold before

its timer expires, the tCUT timer counts back down, but

at 1/16 the rate that it counts up. This allows the current

limit circuitry to tolerate intermittent overload signals with

duty cycles below about 6%; longer duty cycle overloads

will turn the port off.

ICUT is typically set to a lower value than ILIM to allow the

port to tolerate minor faults without current limiting.

Per the IEEE specification, the LTC4266 will automatically

set I

LIM

to 425mA (shown in bold in Table 5) during inrush

at port turn-on, and then switch to the programmed ILIM

setting once inrush has completed. To maintain IEEE com-

pliance, ILIM should kept at 425mA for all Type 1 PDs, and

850mA if a Type 2 PD is detected. ILIM is automatically

reset to 425mA when a port turns off.

Table 5. Example Current Limit Settings

ILIM (mA)

INTERNAL REGISTER SETTING (hex)

RSENSE = 0.5Ω RSENSE = 0.25Ω

53 88

106 08 88

159 89

213 80 08

266 8A

319 09 89

372 8B

425 00 80

478 8E

531 92 8A

584 CB

638 10 90

744 D2 9A

850 40 C0

956 4A CA

1063 50 D0

1169 5A DA

1275 60 E0

1488 52 49

1700 40

1913 4A

2125 50

2338 5A

2550 60

2975 52

PD VOLTAGE (V) AT VPSE = 58V

0.0

PSE CURRENT (A)

0.2

0.4

0.6

10 20 30 40

4266 F14

0.8

1.0

0.1

0.3

0.5

0.7

0.9

802.3af FOLDBACK

2 x 802.3af FOLDBACK

SOA 75ms AT 25°C

SOA DC AT 90°C

PD VOLTAGE (V) AT VPSE = 58V

0.0

PSE CURRENT (A)

0.2

0.4

0.6

10 20 30 40

4266 F15

0.8

1.0

0.1

0.3

0.5

0.7

0.9

LTC4266 FOLDBACK

802.3af FOLDBACK

SOA DC AT 90°C

SOA 75ms AT 90°C

SOA 75ms AT 25°C

Figure 14. Turn On Currents vs FET Safe Operating

Area at 90°C Ambient

Figure 15. LTC4266 Foldback vs FET Safe Operating

Area at 90°C Ambient

LTC4266

4266fg

For more information www.linear.com/LTC4266

ApplicAtions inForMAtion

ILIM Foldback

The LTC4266 features a two-stage foldback circuit that

reduces the port current if the port voltage falls below the

normal operating voltage. This keeps MOSFET power dis-

sipation at safe levels for typical 802.3af MOSFETs, even at

extended 802.3at power levels. Current limit and foldback

behavior are programmable on a per-port basis. Figure

14 shows MOSFET power dissipation with 802.3af-style

foldback compared with a typical MOSFET SOA curve;

Figure 15 demonstrates how two-stage foldback keeps

the FET within its SOA under the same conditions. Table5

gives examples of recommended ILIM register settings.

The LTC4266 will support current levels well beyond the

maximum values in the 802.3at specification. The shaded

areas in Table 5 indicate settings that may require a larger

external MOSFET, additional heat sinking, or a reduced

tLIM setting.

MOSFET Fault Detection

LTC4266 PSE ports are designed to tolerate significant

levels of abuse, but in extreme cases it is possible for the

external MOSFET to be damaged. A failed MOSFET may

short source to drain, which will make the port appear to

be on when it should be off; this condition may also cause

the sense resistor to fuse open, turning off the port but

causing the LTC4266 SENSE pin to rise to an abnormally

high voltage. A failed MOSFET may also short from gate to

drain, causing the LTC4266 GATE pin to rise to an abnor-

mally high voltage. The LTC4266 SENSE and GATE pins

are designed to tolerate up to 80V faults without damage.

If the LTC4266 sees any of these conditions for more than

180μs, it disables all port functionality, reduces the gate

drive pull-down current for the port and reports a FET Bad

fault. This is typically a permanent fault, but the host can

attempt to recover by resetting the port, or by resetting

the entire chip if a port reset fails to clear the fault. If the

MOSFET is in fact bad, the fault will quickly return, and

the port will disable itself again. The remaining ports of

the LTC4266 are unaffected.

An open or missing MOSFET will not trigger a FET Bad

fault, but will cause a tSTART fault if the LTC4266 attempts

to turn on the port.

Voltage and Current Readback

The LTC4266 measures the output voltage and current

at each port with an internal A/D converter. Port data is

only valid when the port power is on. The converter has

two modes:

• Slow mode: 14 samples per second, 14.5 bits resolution

• Fast mode: 440 samples per second, 9.5 bits resolution

In fast mode, the least significant 5 bits of the lower byte

are zeroes so that bit scaling is the same in both modes.

Disconnect

The LTC4266 monitors the port to make sure that the

PD continues to draw the minimum specified current.

A disconnect timer counts up whenever port current is

below 7.5mA (typ), indicating that the PD has been dis-

connected. If the tDIS timer expires, the port will be turned

off and the disconnect bit in the fault event register will be

set. If the current returns before the tDIS timer runs out,

the timer resets and will start counting from the beginning

if the undercurrent condition returns. As long as the PD

exceeds the minimum current level more often than tDIS,

it will stay powered.

Although not recommended, the DC disconnect fea-

ture can be disabled by clearing the corresponding DC

Disconnect Enable bits. Note that this defeats the protec-

tion mechanisms built into the IEEE spec, since a powered

port will stay powered after the PD is removed. If the still-

powered port is subsequently connected to a non-PoE

data device, the device may be damaged.

The LTC4266 does not include AC disconnect circuitry,

but includes AC disconnect enable bits to maintain com-

patibility with the LTC4259A. If the AC Disconnect Enable

bits are set, DC disconnect will be used.

Shutdown Pins

The LTC4266 includes a hardware SHDN pin for each port.

When a SHDN pin is pulled to DGND, the corresponding

port will be shut off immediately. The port remains shut

down until re-enabled via I2C or a device reset in AUTO

pin mode.

LTC4266

4266fg

For more information www.linear.com/LTC4266

Masked Shutdown

The LTC4266 provides a low latency port shedding fea-

ture to quickly reduce the system load when required. By

allowing a pre-determined set of ports to be turned off,

the current on an overloaded main power supply can be

reduced rapidly while keeping high priority devices pow-

ered. Each port can be configured to high or low priority;

all low-priority ports will shut down within 6.5μs after

the MSD pin is pulled low. If multiple ports in a LTC4266

device are shut down via MSD, they are staggered by at

least 0.55μs to help reduce voltage transients on the main

supply. If a port is turned off via MSD, the corresponding

detection and classification enable bits are cleared, so

the port will remain off until the host explicitly re-enables

detection.

SERIAL DIGITAL INTERFACE

Overview

The LTC4266 communicates with the host using a stan-

dard SMBus/I

C 2-wire interface. The LTC4266 is a slave-

only device, and communicates with the host master using

the standard SMBus protocols. Interrupts are signaled to

the host via the INT pin. The timing diagrams (Figures 5

through 9) show typical communication waveforms and

their timing relationships. More information about the

SMBus data protocols can be found at www.smbus.org.

The LTC4266 requires both the VDD and VEE supply rails

to be present for the serial interface to function.

Bus Addressing

The LTC4266’s primary serial bus address is 010xxxxb,

with the lower four bits set by the AD3-AD0 pins; this

allows up to 16 LTC4266s on a single bus. All LTC4266s

also respond to the address 0110000b, allowing the host

to write the same command (typically configuration com-

mands) to multiple LTC4266s in a single transaction. If

the LTC4266 is asserting the INT pin, it will also respond

to the alert response address (0001100b) per the SMBus

spec.

Interrupts and SMBALERT

Most LTC4266 port events can be configured to trigger

an interrupt, asserting the INT pin and alerting the host

to the event. This removes the need for the host to poll

the LTC4266, minimizing serial bus traffic and conserving

host CPU cycles. Multiple LTC4266s can share a com-

mon INT line, with the host using the SMBALERT protocol

(ARA) to determine which LTC4266 caused an interrupt.

For information on serial bus usage and device con-

figuration and status, refer to the LTC4266 Software

Programming documentation.

EXTERNAL COMPONENT SELECTION

Power Supplies and Bypassing

The LTC4266 requires two supply voltages to operate. V

requires 3.3V (nominally) relative to DGND. VEE requires

a negative voltage of between –45V and –57V for Type 1

PSEs, or –51V to –57V for Type 2 PSEs, relative to AGND.

The relationship between the two grounds is not fixed;

AGND can be referenced to any level from VDD to DGND,

although it should typically be tied to either VDD or DGND.

VDD provides power for most of the internal LTC4266 cir-

cuitry, and draws a maximum of 3mA. A ceramic decou-

pling cap of at least 0.1μF should be placed from VDD to

DGND, as close as practical to each LTC4266 chip.

Figure 16 shows a three component low dropout regula-

tor for a negative supply to DGND generated from the

negative VEE supply. VDD is tied to AGND and DGND is

ApplicAtions inForMAtion

Figure 16. Negative LDO to DGND

4266 F16

750k

CMHZ4687-4.3V 0.1µF

CMPTA92

VEE

VDD

LTC4266

AGND

VEE

DGND

10Ω

SMAJ58A

1µF

100V

LTC4266

4266fg

For more information www.linear.com/LTC4266

ApplicAtions inForMAtion

negative referenced to AGND. This regulator drives a sin-

gle LTC4266 device. In Figure 17, DGND is tied to AGND

in this boost converter circuit for a positive VDD supply of

3.3V above AGND. This circuit can drive multiple LTC4266

devices and opto couplers.

VEE is the main supply that provides power to the PDs.

Because it supplies a relatively large amount of power and

is subject to significant current transients, it requires more

design care than a simple logic supply. For minimum IR

loss and best system efficiency, set VEE near maximum

amplitude (57V), leaving enough margin to account for

transient over- or undershoot, temperature drift, and the

line regulation specs of the particular power supply used.

Bypass capacitance between AGND and V

is very impor-

tant for reliable operation. If a short circuit occurs at one

of the output ports it can take as long as 1μs for the

LTC4266 to begin regulating the current. During this time

the current is limited only by the small impedances in the

circuit and a high current spike typically occurs, causing a

voltage transient on the VEE supply and possibly causing

the LTC4266 to reset due to a UVLO fault. A 1μF, 100V

X7R capacitor placed near the VEE pin is recommended

to minimize spurious resets.

Isolating the Serial Bus

The LTC4266 includes a split SDA pin (SDAIN and

SDAOUT) to ease opto-isolation of the bidirectional SDA

line.

IEEE 802.3 Ethernet specifications require that network

segments (including PoE circuitry) be electrically isolated

from the chassis ground of each network interface device.

However, network segments are not required to be iso-

lated from each other, provided that the segments are

connected to devices residing within a single building on

a single power distribution system.

For simple devices such as small PoE switches, the isola-

tion requirement can be met by using an isolated main

power supply for the entire device. This strategy can be

used if the device has no electrically conducting ports

other than twisted-pair Ethernet. In this case, the SDAIN

and SDAOUT pins can be tied together and will act as a

standard I2C/SMBus SDA pin.

If the device is part of a larger system, contains additional

external non-Ethernet ports, or must be referenced to pro-

tective ground for some other reason, the Power over

Ethernet subsystem (including all LTC4266s) must be

Figure 17. Positive VDD Boost Converter

4266 F17

R54

56k

C79

2200pF

GND

ITH/RUN

LTC3803

VCC

VFB

NGATE Q15

FDC2512

Q13

FMMT723

Q14

FMMT723

SENSE

C74

100µF

6.3V

C75

10µF

16V

100µH

SUMIDA CDRH5D28-101NC

R51

4.7k

R53

4.7k

R52

3.32k

3.3V AT 400mA

R55

806Ω

R59

0.100Ω

1%, 1W

R56

47.5k

R57

D28

B1100

R58

10Ω

R60

10Ω

C73

10µF

6.3V

10µH

SUMIDA CDRH4D28-100NC

C77

0.22µF

100V

C78

0.22µF

100V

C76

10µF

100V

LTC4266

4266fg

For more information www.linear.com/LTC4266

ApplicAtions inForMAtion

Figure 18. Opto-Isolating the I2C Bus

4266 F18

VDD

INT

SCL

SDAIN

SDAOUT

AD0

AD1

AD2

AD3

DGND

AGND

LTC4266

0.1µF

200Ω

HCPL-063L

VDD CPU

SCL

SDA

SMBALERT

GND CPU

U1: FAIRCHILD NC7WZ17

U2, U3: AGILENT HCPL-063L

CONTROLLER

0100000

0100001

0100010

0101111

I2C ADDRESS

0.1µF

10Ω

SMAJ58A 1µF

100V

VEE

SMAJ5.0A

ISOLATED

3.3V

ISOLATED

GND

ISOLATED

–54V

10µF

TVSBULK

CBULK

VDD

INT

SCL

SDAIN

SDAOUT

AD0

AD1

AD2

AD3

DGND

AGND

LTC4266

0.1µF

10Ω

SMAJ58A 1µF

100V

VEE

SMAJ5.0A

VDD

INT

SCL

SDAIN

SDAOUT

AD0

AD1

AD2

AD3

DGND

AGND

LTC4266

0.1µF

10Ω

SMAJ58A 1µF

100V

VEE

SMAJ5.0A

VDD

INT

SCL

SDAIN

SDAOUT

AD0

AD1

AD2

AD3

DGND

AGND

LTC4266

0.1µF

10Ω

SMAJ58A 1µF

100V

VEE

SMAJ5.0A

•

LTC4266

4266fg

For more information www.linear.com/LTC4266

electrically isolated from the rest of the system. Figure 18

shows a typical isolated serial interface. The SDAOUT pin

of the LTC4266 is designed to drive the inputs of an opto-

coupler directly. Standard I

C/SMBus devices typically

cannot drive opto-couplers, so U1 is used to buffer the

signals from the host controller side.

External MOSFET

Careful selection of the power MOSFET is critical to system

reliability. LTC recommends either Fairchild IRFM120A,

FDT3612, FDMC3612 or Philips PHT6NQ10T for their

proven reliability in Type 1 and Type 2 PSE applications.

Non-standard applications that provide more current

than the 850mA IEEE maximum may require heat sink-

ing and other MOSFET design considerations. Contact

LTC Applications before using a MOSFET other than one

of these recommended parts.

Sense Resistor

The LTC4266 is designed to use either 0.5Ω or 0.25Ω

current sense resistors. For new designs 0.25Ω is recom-

mended to reduce power dissipation; the 0.5Ω option is

intended for existing systems where the LTC4266 is used

as a drop-in replacement for the LTC4258 or LTC4259A.

The lower sense resistor values reduce heat dissipation.

Four commonly available 1Ω resistors (0402 or larger

package size) can be used in parallel in place of a single

0.25Ω resistor. In order to meet the ICUT and ILIM accuracy

required by the IEEE specification, the sense resistors

should have ±1% tolerance or better, and no more than

±200ppm/°C temperature coefficient.

Output Cap

Each port requires a 0.22μF cap across its outputs to keep

the LTC4266 stable while in current limit during startup

or overload. Common ceramic capacitors often have sig-

nificant voltage coefficients; this means the capacitance

is reduced as the applied voltage increases. To minimize

this problem, X7R ceramic capacitors rated for at least

100V are recommended.

Surge Protection

Ethernet ports can be subject to significant cable surge

events. To keep PoE voltages below a safe level and pro-

tect the application against damage, protection compo-

nents, as shown in Figure 19, are required at the main

supply, at the LTC4266 pins, and at each port.

Bulk transient voltage suppression (TVSBULK) and bulk

capacitance (C

BULK

) are required across the main PoE

supply and should be sized to accommodate system

level surge requirements. A large capacitance of 10μF or

greater (C3) is required across the +3.3V supply if VDD

is above AGND.

Each LTC4266 requires a 10Ω, 0805 resistor (R1) in series

from supply AGND to the LTC4266 AGND pin. Across the

LTC4266 AGND pin and VEE pin are an SMAJ58A, 58V

TVS (D1) and a 1μF, 100V bypass capacitor (C1). These

components must be placed close to the LTC4266 pins.

If the VDD supply is above AGND, each LTC4266 requires

a 10Ω, 0805 resistor (R2) in series from the +3.3V supply

positive rail to the LTC4266 V

pin. Across the LTC4266

ApplicAtions inForMAtion

Figure 19. LTC4266 Surge Protection

D4 S1B

COUT

0.22μF

100V

X7R

1µF

100V

X7R

VEE SENSE GATE OUT

VDD

AUTO

SCL

SDAIN

DGND

AGND

1/4

LTC4266

–54V

4266 F19

S1B

OUTn

TO PORT

0.1µF

SMAJ5.0A

10Ω

10µF

CBULK

TVSBULK

+3.3V

SMAJ58A

10Ω

LTC4266

4266fg

For more information www.linear.com/LTC4266

ApplicAtions inForMAtion

VDD pin and DGND pin are an SMAJ5.0A, 5.0V TVS (D2)

and a 0.1μF capacitor (C2). These components must be

placed close to the LTC4266 pins. DGND is tied directly

to the protected AGND pin. Pull-ups at the logic pins

should be to the protected side of the 10Ω resistors at

the V

pin. Pull-downs at the logic pins should be to

the protected side of the 10Ω resistors at the tied AGND

and DGND pins.

Finally, each port requires a pair of S1B clamp diodes, one

from OUTn to supply AGND (D3) and one from OUTn to

supply VEE (D4). The diodes at the ports steer harmful

surges into the supply rails where they are absorbed by

the surge suppressors and the VEE bypass capacitance.

The layout of these paths must be low impedance.

Further considerations include LTC4266 applications

with off-board connections, such as a daughter card to

a mother board or headers to an external supply or host

control board. Additional protection may be required at

the LTC4266 pins to these off-board connections.

LAYOUT GUIDELINES

Standard power layout guidelines apply to the LTC4266:

place the decoupling caps for the VDD and VEE supplies

near their respective supply pins, use ground planes, and

use wide traces wherever there are significant currents.

The main layout challenge involves the arrangement of

the current sense resistors, and their connections to the

LTC4266. Because the sense resistor values are very

low, layout parasitics can cause significant errors. Care

is required to achieve specified accuracy, particularly with

disconnect currents.

Figure 20 illustrates the problem. In the example on the

left, two ports have load currents I1 and I2 that return to

the V

power supply through a mutual resistance R

represents the combined resistances of any traces,

planes, and vias in the PCB that I1 and I2 share as they

return to the V

supply. The LTC4266 measures the volt-

age difference between its SENSE and VEE pins to sense

the voltage drop across RS1, but as the example shows,

RM introduces errors.

Figure 20. Layout Affects Current Readback Accuracy

RS1

MUTUAL RESISTANCE

RS2

4266 F20

IEE

– –

I1I2

I1 + I2 + IEE

VS = I1RS1 + I1RM + I2RM

LTC4266

GATE

SENSE

SIGNAL

SCALE ERROR

CROSSTALK ERROR

VEE

RKRM

RS1

KELVIN SENSE LINE

RS2

IEE

I1I2

VS = I1RS1 – IEERK

I1 + I2 + IEE

LTC4266

GATE

SENSE

SIGNAL

SMALL OFFSET ERROR

VEE

LTC4266

4266fg

For more information www.linear.com/LTC4266

Figure 21. Layout Strategy to Reduce Mutual Resistance

LTC4266

PORTS A THROUGH D

SENSE1

SENSE2

SENSE3

SENSE4

VEE

VIA VIA

4266 F21

BY KEEPING THESE COPPER FILLS SEPARATE ON

THE SURFACE, MUTUAL RESISTANCE BETWEEN

PORTS A-D AND E-H IS ELIMINATED

THIS TRACE PROVIDES VEE TO U1

BUT ALSO ACTS AS A KELVIN

SENSE LINE FOR PORTS A-D

VEE COPPER FILL ON SURFACE LAYER

VEE PLANE ON INNER LAYER

LTC4266

PORTS E THROUGH H

SENSE1

SENSE2

SENSE3

SENSE4

VEE RSENSE

RETURN TO

VEE POWER SUPPLY

ApplicAtions inForMAtion

The example on the right shows how errors can be mini-

mized with a good layout. The circuit is rearranged so

that RM no longer affects VS, and the VEE connection to

the LTC4266 is used as a Kelvin sense trace. VEE is not

a perfect Kelvin connection because all four ports con-

trolled by the LTC4266 share the same sense trace, and

because the current through the trace (IEE) is not zero.

However, as the equation shows, the remaining error is a

small offset term.

Figure 21 shows two LTC4266 chips controlling eight

ports (A though H). The ports are separated into two

groups of four; each has its own trace on the top PCB

layer that connects to the VEE plane with a via. Currents

from the U1 sub-circuit are effectively isolated from the

U2 sub-circuit, reducing the layout problem down to

4-port chunks; this arrangement can be expanded for

any number of ports.

Figure 22 shows an example of good 4-port layout. Each

0.25Ω sense resistor consists of four 1Ω resistors in

parallel. The four groups of resistors are arranged to

minimize the overlap in their current flows, which mini-

mizes mutual resistance. The horizontal slits cut in the

copper help to keep the currents separate. Wide copper

paths connect each group of resistors to the vias at the

center, so the resistance is very low.

Proper connection of the sense line is also important. In

Figure 22, U1 is not connected directly to the VEE plane

but is connected instead to a Kelvin sense trace that leads

to the sense resistor array. Similarly, the via at the center

of the sense resistor array has a matching hole in the

VEE plane. This arrangement prevents the mutual resis-

tance of the four large vias from influencing the current

measurements.

LTC4266

4266fg

For more information www.linear.com/LTC4266

Figure 22. Good PCB Layout Example

4266 F22

PORT A RSENSE PORT B RSENSE

FOUR LARGE VIAS

TO VEE PLANE

PIN 1

U1 THE PADDLE IS

CONNECTED TO

VEE PINS

KELVIN SENSE TRACE CONNECTS U1

TO VEE THROUGH THE VIAS ON THE RIGHT

EDGE OF VEE PLANE (ON SOME INNER LAYER)

VIAS TO SOURCE PIN OF

THE PORT D MOSFET

LOCATED ON THE OPPOSITE

SIDE OF THE BOARD

HOLE IN VEE PLANE

PORT C RSENSE PORT D RSENSE

ApplicAtions inForMAtion

LTC4266

4266fg

For more information www.linear.com/LTC4266

pAckAge Description

GW36 SSOP 0204

0° – 8° TYP

0.355

REF

0.231 – 0.3175

(.0091 – .0125)

0.40 – 1.27

(.015 – .050)

7.417 – 7.595**

(.292 – .299)

× 45°

0.254 – 0.406

(.010 – .016)

2.286 – 2.388

(.090 – .094)

0.1 – 0.3

(.004 – .0118)

2.44 – 2.64

(.096 – .104)

0.800

(.0315)

BSC

0.28 – 0.51

(.011 – .02)

TYP

15.291 – 15.545*

(.602 – .612)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

10.11 – 10.55

(.398 – .415)

36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19

10.804 MIN

RECOMMENDED SOLDER PAD LAYOUT

7.75 – 8.258

1936

181

0.800 BSC0.520 ±0.0635

1.40 ±0.127

DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH

SHALL NOT EXCEED 0.152mm (0.006") PER SIDE

DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD

FLASH SHALL NOT EXCEED 0.254mm (0.010") PER SIDE

MILLIMETERS

(INCHES)

NOTE:

1. CONTROLLING DIMENSION: MILLIMETERS

2. DIMENSIONS ARE IN

GW Package

36-Lead Plastic SSOP (Wide .300 Inch)

(Reference LTC DWG # 05-08-1642)

Please refer to http://www.linear.com/product/LTC4266#packaging for the most recent package drawings.

LTC4266

4266fg

For more information www.linear.com/LTC4266

pAckAge Description

5.00 ±0.10

NOTE:

1. DRAWING CONFORMS TO JEDEC PACKAGE

OUTLINE M0-220 VARIATION WHKD

2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

PIN 1

TOP MARK

(SEE NOTE 6)

BOTTOM VIEW—EXPOSED PAD

5.50 REF

5.15 ±0.10

7.00 ±0.10

0.75 ±0.05

R = 0.125

TYP

R = 0.10

TYP

0.25 ±0.05

(UH) QFN REF C 1107

0.50 BSC

0.200 REF

0.00 – 0.05

RECOMMENDED SOLDER PAD LAYOUT

APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED

3.00 REF

3.15 ±0.10

0.40 ±0.10

0.70 ±0.05

0.50 BSC

5.5 REF

3.00 REF 3.15 ±0.05

4.10 ±0.05

5.50 ±0.05 5.15 ±0.05

6.10 ±0.05

7.50 ±0.05

0.25 ±0.05

PACKAGE

OUTLINE

4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE

MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm ON ANY SIDE

5. EXPOSED PAD SHALL BE SOLDER PLATED

6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION

ON THE TOP AND BOTTOM OF PACKAGE

PIN 1 NOTCH

R = 0.30 TYP OR

0.35 × 45° CHAMFER

UHF Package

38-Lead Plastic QFN (5mm × 7mm)

(Reference LTC DWG # 05-08-1701 Rev C)

Please refer to http://www.linear.com/product/LTC4266#packaging for the most recent package drawings.

LTC4266

4266fg

For more information www.linear.com/LTC4266

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

revision history

REV DATE DESCRIPTION PAGE NUMBER

B 3/11 Revised AGND and DGND pin references throughout data sheet.

Revised auto mode to AUTO pin mode throughout data sheet.

Added text to Operating Modes and made minor text edits throughout Applications Information section.

1 to 6, 9, 13

1 to 26

19 to 26

C 8/11 Changed –48 Supply Voltage to Main PoE Supply Voltage.

Changed Gate Typical voltage to 12V.

Changed SCL, SDAIN VIL to 1.0V (I2C compliance).

Fix tCUT to differentiate from tLIM, Electrical Characteristics.

Added (mA) to Classification Current Compliance, x-axis title.

802.3af Classification section, changed Figure 14 reference to Figure 13.

Power Supplies and Bypassing section changed to –45 for Type 1 minimum and –51 for Type 2 minimum.

3, 13, 19

D 1/12 Revised MAX value for VILD I2C Input Low Voltage

Clarified AUTO pin mode relationship to reset pin

E 5/14 Fixed part marking for GW package. 2

F 06/15 Updated surge protection recommendations

Simplified Power over Ethernet system diagram

Updated Figure numbers

Added component value (Figure 17)

1, 22, 24, 25, 30

25 to 27

G 06/17 Updated Figures 16 and 19 22, 25

(Revision history begins at Rev B)

LTC4266

4266fg

For more information www.linear.com/LTC4266

 LINEAR TECHNOLOGY CORPORATION 2009

LT 0617 REV G • PRINTED IN USA

www.linear.com/LTC4266

relAteD pArts

PART NUMBER DESCRIPTION COMMENTS

LTC3803 Constant Frequency Current Mode Flyback DC/DC

Controller in ThinSOT™

200kHz Operation, Adjustable Slope Compensation

LTC4258 Quad IEEE 802.3af PoE PSE Controller DC Disconnect Sensing Only

LTC4263 Single IEEE 802.3af PSE Controller Internal FET Switch

LTC4265 IEEE 802.3at PD Interface Controller 100V, 1A Internal Switch, 2-Event Classification Recognition

LTC4266A Quad LTPoE++ PSE Controller Up to 90W, Backwards Compatible with IEEE 802.3af and IEEE 802.3at PDs

LTC4266C Quad IEEE 802.3af PSE Controller Programmable ICUT/ILIM, 1-Event Classification

LTC4267 IEEE 802.3af PD Interface With Integrated Switching

Regulator

Internal 100V, 400mA Switch, Dual Inrush Current, Programmable Class

LTC4269-1 IEEE 802.3at PD Interface Integrated Switching Regulator 2-Event Classification, Programmable Classification, Synchronous No-Opto

Flyback Controller, 50kHz to 250kHz

LTC4269-2 IEEE 802.3at PD Interface Integrated Switching Regulator 2-Event Classification, Programmable Classification, Synchronous Forward

Controller, 100kHz to 500kHz

One Complete Isolated Powered Ethernet Port

typicAl ApplicAtion

4266 TA02

0.1µF

200Ω

HCPL-063L

VDD CPU

SCL

SDA

GND CPU

INTERRUPT

CONTROLLER

PHY

(NETWORK

PHYSICAL

LAYER

CHIP)

VEE SENSE GATE OUT

DGND

SCL

SDAIN

SDAOUT

INT

AGND

RSENSE

0.25Ω

1/4

LTC4266

VDD

ISOLATED

–54V S1B

ISOLATED

3.3V

0.01µF

200V

0.01µF

200V

0.01µF

200V

0.01µF

200V

75Ω75Ω

RJ45

CONNECTOR

1000pF

2000V

•

•• ••

•

FB1

FB2

Q1: FAIRCHILD IRFM120A OR PHILIPS PHT6NQ10T

U1: FAIRCHILD NC7WZ17

U2, U3: AGILENT HCPL-063L

FB1, FB2: TDK MPZ2012S601A

T1: PULSE H6096NL OR COILCRAFT ETH1-230LD

0.1µF

S1B

0.22µF

100V

X7R

CBULK

TVSBULK

SMAJ58A

10Ω

1µF

100V

X7R

0.1µF

SMAJ5.0A

10Ω

10µF