LT4276BHUFD#TRPBF - ANALOG DEVICES

LT4276

4276fa

For more information www.linear.com/LT4276

Typical applicaTion

FeaTures DescripTion

LTPoE++/PoE+/PoE

PD Forward/Flyback Controller

The LT

4276 is a pin-for-pin compatible family of IEEE

802.3 and LTPoE++ Powered Device (PD) controllers. It

includes an isolated switching regulator controller capable

of synchronous operation in both forward and flyback

topologies with auxiliary power support.

The LT4276A employs the LTPoE++ classification scheme,

receiving 38.7W, 52.7W, 70W or 90W of power at the PD

RJ45 connector, and is backwards compatible with IEEE

802.3. The LT4276B is a fully 802.3at compliant, 25.5W

Type 2 (PoE+) PD. The LT4276C is a fully 802.3af compli-

ant, 13W Type 1 (PoE) PD.

The LT4276 supports both forward and flyback power

supply topologies, configurable for a wide range of PoE

applications. The flyback topology supports No-Opto

feedback. Auxiliary input voltage can be accurately sensed

with just a resistor divider connected to the AUX pin.

The LT4276 utilizes an external, low RDS(ON) N-channel

MOSFET for the Hot Swap function, maximizing power

delivery and efficiency, reducing heat dissipation, and

easing the thermal design.

LTPoE++ 70W Power Supply in a Forward Mode

applicaTions

n IEEE802.3af/at and LTPoE++

™

90W Powered Device

(PD) with Forward/Flyback Controller

n LT4276A Supports All of the Following Standards:

n LTPoE++ 38.7W, 52.7W, 70W and 90W

n IEEE 802.3at 25.5W Compliant

n IEEE 802.3af up to 13W Compliant

n LT4276B is IEEE 802.3at/af Compliant

n LT4276C is IEEE 802.3af Compliant

n Superior Surge Protection (100V Absolute Maximum)

n Wide Junction Temperature Range (–40°C to 125°C)

n Auxiliary Power Support as Low as 9V

n No Opto-Isolator Required for Flyback Operation

n External Hot Swap

™

N-Channel MOSFET for Lowest

Power Dissipation and Highest System Efficiency

n >94% End-to-End Efficiency with LT4321 Ideal Bridge

n Available in a 28-Lead 4mm × 5mm QFN Package

n High Power Wireless Data Systems

n Outdoor Security Camera Equipment

n Commercial and Public Information Displays

n High Temperature Applications L, LT, LTC, LTM, LTPoE++, Linear Technology and the Linear logo are registered trademarks of

Linear Technology Corporation. All other trademarks are the property of their respective owners.

LT4276 Family

MAX DELIVERED

POWER

LT4276

GRADE

ABC

LTPoE++ 90W l

LTPoE++ 70W l

LTPoE++ 52.7W l

LTPoE++ 38.7W l

25.5W l l

13W lll

••

VPORT

RCLASS

AUX

RCLASS++

VCC VCC

VIN

VCC

0.1µF

10µFBAV19WS

(TRR ≤50ns)

22µF

GATE HS

SRC FFS

DLY PG

ITHB

TO MICROPROCESSOR

ISEN+

ISEN–

4276 TA01

GND FB31 ROSC T2PSS

100µH

AUX

37V-57V

–

FMMT723

20mΩ

13A

–

3.3k

10k

0.1µF 100pF

10nF

100k

LT4276A

OPTO

LT4276

4276fa

For more information www.linear.com/LT4276

pin conFiguraTionabsoluTe MaxiMuM raTings

VPORT, HSSRC, VIN Voltages .....................–0.3 to 100V

HSGATE Current.................................................. ±20mA

VCC Voltage .................................................... –0.3 to 8V

RCLASS, RCLASS++

Voltages .................................–0.3 to 8V (and ≤ VPORT)

SFST, FFSDLY, ITHB, T2P Voltages ......–0.3 to VCC+0.3V

ISEN+, ISEN– Voltages ........................................... ±0.3V

FB31 Voltage ..................................................+12V/–30V

RCLASS/RCLASS++ Current .............................. –50mA

AUX Current ........................................................ ±1.4mA

ROSC Current .....................................................±100µA

RLDCMP Current ................................................±500µA

T2P Current .........................................................–2.5mA

Operating Junction Temperature Range (Note 3)

LT4276AI/LT4276BI/LT4276CI ..............–40°C to 85°C

LT4276AH/LT4276BH/LT4276CH ....... –40°C to 125°C

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

(Notes 1, 2)

9 10

TOP VIEW

UFD PACKAGE

28-LEAD (4mm × 5mm) PLASTIC QFN

11 12 13

28 27 26 25 24

GND

AUX

RCLASS++/NC*

RCLASS

T2P/NC**

VCC

DNC

VCC

GND

ISEN+

ISEN–

RLDCMP

VPORT

HSGATE

HSSRC

VIN

SWVCC

VCC

ROSC

SFST

FFSDLY

ITHB

FB31

815

GND

TJMAX = 150°C, θJC = 3.4°C/W

EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB

*RCLASS++ is not connected in the LT4276B and LT4276C

**T2P is not connected in the LT4276C

orDer inForMaTion

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

LT4276AIUFD#PBF LT4276AIUFD#TRPBF 4276A 90W 28-Lead (4mm × 5mm) Plastic QFN –40°C to 85°C

LT4276AHUFD#PBF LT4276AHUFD#TRPBF 4276A 90W 28-Lead (4mm × 5mm) Plastic QFN –40°C to 125°C

LT4276BIUFD#PBF LT4276BIUFD#TRPBF 4276B 25.5W 28-Lead (4mm × 5mm) Plastic QFN –40°C to 85°C

LT4276BHUFD#PBF LT4276BHUFD#TRPBF 4276B 25.5W 28-Lead (4mm × 5mm) Plastic QFN –40°C to 125°C

LT4276CIUFD#PBF LT4276CIUFD#TRPBF 4276C 13W 28-Lead (4mm × 5mm) Plastic QFN –40°C to 85°C

LT4276CHUFD#PBF LT4276CHUFD#TRPBF 4276C 13W 28-Lead (4mm × 5mm) Plastic QFN –40°C to 125°C

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

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.

LT4276

4276fa

For more information www.linear.com/LT4276

elecTrical characTerisTics

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VPORT, HSSRC, VIN Operating Voltage At VPORT Pin l60 V

VSIG VPORT Signature Range At VPORT Pin l1.5 10 V

VCLASS VPORT Classification Range At VPORT Pin l12.5 21 V

VMARK VPORT Mark Range At VPORT Pin, After 1st Classification Event l5.6 10 V

VPORT AUX Range At VPORT Pin, VAUX ≥ 6.45V l8 60 V

Signature/Class Hysteresis Window l1.0 V

Reset Threshold l2.6 5.6 V

VHSON Hot Swap Turn-On Voltage l 35 37 V

VHSOFF Hot Swap Turn-Off Voltage l 30 31 V

Hot Swap On/Off Hysteresis Window l3 V

Supply Current

VPORT, HSSRC & VIN Supply Current VVPORT = VHSSRC = VVIN = 60V l2 mA

VPORT Supply Current During Classification VVPORT = 17.5V, RCLASS, RCLASS++ Open l0.7 1.0 1.3 mA

VPORT Supply Current During Mark Event VVPORT = VMARK after 1st Classification Event l0.4 2.2 mA

Signature and Classification

Signature Resistance VSIG (Note 4) l23.6 24.4 25.5 kΩ

Signature Resistance During Mark Event VMARK (Note 4) l5.2 8.3 11.4 kΩ

RCLASS/RCLASS++ Voltage –10mA ≥ IRCLASS ≥ –36mA l1.36 1.40 1.43 V

Classification Stability Time VVPORT Step to 17.5V, RCLS = 35.7Ω l2 ms

Digital Interface

VAUXT AUX Threshold VPORT = 17.5V, VIN = VHSSRC = 18.5V l6.05 6.25 6.45 V

IAUXH AUX Pin Current VAUX = 6.05V, VPORT = 17.5V, VIN = 9V, VCC = 0V l3.3 5.3 7.3 µA

T2P Output High VVCC - VT2P, –1mA Load l0.3 V

T2P Leakage VT2P = 0V l–1 1 µA

Hot Swap Control

IGPU HSGATE Pull Up Current VHSGATE - VHSSRC = 5V (Note 5) l–27 –22 –18 µA

HSGATE Voltage –10µA Load, with respect to HSSRC l10 14 V

HSGATE Pull Down Current VHSGATE - VHSSRC = 5V l400 µA

VCC Supply

VCCREG VCC Regulation Voltage l7.2 7.6 8.0 V

Feedback Amplifier

VFB FB31 Regulation Voltage l3.11 3.17 3.23 V

FB31 Pin Bias Current RLDCMP Open -0.1 µA

gm Feedback Amplifier Average Trans-

Conductance Time Average, –2µA < IITHB < 2µA l–52 –40 –26 µA/V

ISINK ITHB Average Sink Current Time Average, VFB31 = 0V l4.4 8.0 13.4 µA

Soft-Start

ISFST Charging Current VSFST = 0.5V, 3.0V l–49 –42 –36 µA

The l denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TJ = 25°C. VVPORT = VHSSRC = VVIN = 40V, VVCC = VCCREG, ROSC, PG, and SG Open,

RFFSDLY = 5.23kΩ to GND. AUX connected to GND unless otherwise specified. (Note 2)

LT4276

4276fa

For more information www.linear.com/LT4276

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Gate Outputs

PG, SG Output High Level I = –1mA lVCC –0.1 V

PG, SG Output Low Level I = 1mA l1 V

PG Rise Time, Fall Time PG = 1000pF 15 ns

SG Rise Time, Fall Time SG = 400pF 15 ns

Current Sense/Overcurrent

VFAULT Overcurrent Fault Threshold VISEN+ - VISEN–l125 140 155 mV

ΔVSENSE/

ΔVITHB

Current Sense Comparator Threshold with

Respect to VITHB

l–130 –111 –98 mV/V

VITHB(OS) VITHB Offset l3.03 3.17 3.33 V

Timing

fOSC Default Switching Frequency ROSC Pin Open l 200 214 223 kHz

Switching Frequency ROSC = 45.3kΩ to GND l280 300 320 kHz

fT2P LTPoE++ Signal Frequency fSW/256

tMIN Minimum PG On Time l175 250 330 ns

DMAX Maximum PG Duty Cycle l63 66 70 %

tPGDELAY PG Turn-On Delay-Flyback

PG Turn-On Delay-Forward

5.23kΩ from FFSDLY to GND

52.3kΩ from FFSDLY to GND

10.5kΩ from FFSDLY to VCC

52.3kΩ from FFSDLY to VCC

171

391

tFBDLY Feedback Amp Enable Delay Time 350 ns

tFB Feedback Amp Sense Interval 550 ns

tPGSG PG Falling to SG Rising Delay Time-Flyback

PG Falling to SG Falling Delay Time-

Forward

Resistor from FFSDLY to GND

10.5kΩ from FFSDLY to VCC

52.3kΩ from FFSDLY to VCC

301

tSTART Start Timer (Note 6) Delay After Power Good l80 86 93 ms

tFAULT Fault Timer (Note 6) Delay After Overcurrent Fault l80 86 93 ms

IMPS MPS Current l10 12 14 mA

elecTrical characTerisTics

The l denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TJ = 25°C. VVPORT = VHSSRC = VVIN = 40V, VVCC = VCCREG, ROSC, PG, and SG Open,

RFFSDLY = 5.23kΩ to GND. AUX connected to GND unless otherwise specified. (Note 2)

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. All voltages with respect to GND unless otherwise noted. Positive

currents are into pins; negative currents are out of pins unless otherwise

noted.

Note 3. This IC includes overtemperature protection that is intended

to protect the device during momentary overload conditions. Junction

temperature can exceed 150°C when overtemperature protection is active.

Continuous operation above the specified maximum operating junction

temperature may impair device reliability.

Note 4. Signature resistance specifications do not include resistance

added by the external diode bridge which can add as much as 1.1kΩ to the

port resistance.

Note 5. IGPU available in PoE powered operation. That is, available after

V(VPORT) > VHSON and V(AUX) < VAUXT, over the range where V(VPORT)

is between VHSOFF and 60V.

Note 6. Guaranteed by design, not subject to test.

LT4276

4276fa

For more information www.linear.com/LT4276

Typical perForMance characTerisTics

VFB31 vs Temperature

Feedback Amplifier Output Current

vs VFB31

Switching Frequency

vs Temperature

Current Sense Voltage

vs Duty Cycle, ITHB

PG Delay Time vs Temperature in

Flyback Mode

PG Delay Time vs Temperature in

Forward Mode

Input Current vs Input Voltage

25k Detection Range

Signature Resistance

vs Input Voltage VCC Current vs Temperature

VPORT VOLTAGE (V)

VPORT CURRENT (mA)

0.4

0.3

0.2

0.1

0.5

6 8 102 4

4276 G01

125°C

85°C

25°C

–40°C

VPORT VOLTAGE (V)

23.75

SIGNATURE RESISTANCE (kΩ)

25.75

25.25

24.75

24.25

26.25

65 87 92 43

4276 G02

125°C

85°C

25°C

–40°C

TEMPERATURE (°C)

–50

VCC CURRENT (mA)

5025 10075 1250–25

4276 G03

214KHz

300KHz

TEMPERATURE (°C)

–50

3.162

VFB31 (V)

3.176

3.174

3.172

3.170

3.168

3.166

3.164

3.178

5025 10075 1250–25

4276 G04

FB31 VOLTAGE (V)

2.57

–15

ITHB CURRENT (µA)

–5

–10

3.17 3.37 3.57 3.772.77 2.97

4276 G05

125°C

85°C

25°C

–40°C

TEMPERATURE (°C)

–50

175

FREQUENCY (kHz)

300

275

250

225

200

325

5025 10075 1250–25

4276 G06

ROSC = 45.3k

ROSC OPEN

VITHB = 1.8V

VITHB = 2.3V

VITHB = 2.6V

VITHB = 2.9V

DUTY CYCLE (%)

V(ISEN+ - ISEN–) (mV)

140

100

120

160

4030 6050 702010

4276 G07

VITHB = 0.96V (FB31 = 0V)

TEMPERATURE (°C)

–50

PG DELAY TIME (ns)

200

150

100

250

5025 10075 1250–25

4276 G08

RFFSDLY = 5.23k

RFFSDLY = 52.3k

TPGDELAY, RFFSDLY = 10.5k

TPGSG, RFFSDLY = 10.5k

TPGSG, RFFSDLY = 52.3k

TPGDELAY, RFFSDLY = 52.3k

TEMPERATURE (°C)

–50

DELAY TIME (ns)

350

200

250

300

150

100

400

5025 10075 1250–25

4276 G09

LT4276

4276fa

For more information www.linear.com/LT4276

pin FuncTions

GND(Pins 1, 19, Exposed Pad Pin 29): Device Ground.

Exposed Pad must be electrically and thermally connected

to PCB GND and Pin 19.

RCLASS++ (Pin 3, LT4276A Only): LTPoE++ Class Select

Input. Connect a resistor between RCLASS++ to GND per

Table 1.

AUX (Pin 2): Auxiliary Sense. Assert AUX via a resistive

divider from the auxiliary power input to set the voltage

at which the auxiliary supply takes over. Asserting AUX

pulls down HSGATE, disconnects the signature resistor

and disables classification. The AUX pin sinks IAUXH when

below its threshold voltage of VAUXT to provide hysteresis.

Connect to GND if not used.

RCLASS (Pin 4): Class Select Input. Connect a resistor

between RCLASS to GND per Table 1.

T2P (Pin 5, LT4276A and LT4276B only): PSE Type Indica-

tor. Low impedance to VCC indicates 2-event classification.

Alternating low/high impedance indicates LTPoE++ clas-

sification (LT4276A only, see Applications Information).

High impedance indicates 1-event classification. This pin

is not connected on the LT4276C. See the Applications

Information Section for pin behavior when using the AUX

pin.

DNC (Pin 22): Do Not Connect. Leave pin open.

ROSC (Pin 10): Programmable Frequency Adjustment.

Resistor to GND programs operating frequency. Leave

open for default frequency of 214kHz.

SFST (Pin 11): Soft-Start. Capacitor to GND sets soft-

start timing.

FFSDLY (Pin 12): Forward/Flyback Select and Primary

Gate Delay Adjustment. Resistor to GND adjusts gate drive

delay for a flyback topology. Resistor to VCC adjusts gate

drive delay for a forward topology.

ITHB (Pin 13): Current Threshold Control. The voltage on

this pin corresponds to the peak current of the external

FET. Note that the voltage gain from ITHB to the input of

the current sense comparator (VSENSE) is negative.

FB31 (Pin 14): Feedback Input. In flyback mode, connect

external resistive divider from the third winding feedback.

Reference voltage is 3.17V. Connect to GND in forward

mode.

RLDCMP (Pin 15): Load Compensation Adjustment. Op-

tional resistor to GND controls output voltage set point

as a function of peak switching current. Leave RLDCMP

open if load compensation is not needed.

ISEN– (Pin 16): Current Sense, Negative Input. Route as

a dedicated trace to the current sense resistor.

ISEN+ (Pin 17): Current Sense, Positive Input. Route as

a dedicated trace to the current sense resistor.

SG (Pin 18): Secondary (Synchronous) Gate Drive, Output.

PG (Pin 20): Primary Gate Drive, Output.

VCC (Pins 6, 7, 8, 9, 21): Switching Regulator Controller

Supply Voltage. Connect a local 1µF ceramic capacitor

from VCC pin 21 to GND pin 19 as close as possible to

LT4276 as shown in Table 2.

SWVCC(Pin 23): Switch Driver for VCC’s Buck Regulator.

This pin drives the base of a PNP in a buck regulator to

generate VCC.

VIN (Pin 24): Buck Regulator Supply Voltage. Usually

separated from HSSRC by a pi filter.

HSSRC (Pin 25): External Hot Swap MOSFET Source.

Connect to source of the external MOSFET.

HSGATE (Pin 26): External Hot Swap MOSFET Gate Con-

trol, Output. Capacitance to GND determines inrush time.

NC (Pin 27): No Connection. Not internally connected.

VPORT (Pin 28): PD Interface Supply Voltage and External

Hot Swap MOSFET Drain Connection.

LT4276

4276fa

For more information www.linear.com/LT4276

block DiagraM

–

SLOPE

COMP

OSC

TSD

SWITCHING

REGULATOR

CONTROLLER

PD INTERFACE

CONTROLLER

START-UP

REGULATOR

INTERNAL

BUCK

CONTROLLER

1.4V

HSGATE

HSSRC

11V

VPORT

VPORT SWVCCVIN

VCC

ITHB

SFST

FFSDLY

ROSC

ISEN+

ISEN–

4276 BD

T2P

GND

VCC

VPORT

RCLASS

RCLASS++

AUX

VAUXT

IAUXH

FB31

RLDCMP

FEEDBACK AMP

gm = –40µA/V

LOAD

COMP

CURRENT

FAULT

COMPARATOR

CURRENT

SENSE

COMPARATOR

VFB

VFAULT

AV = 10

AV = 1

VCC

VSENSE

VITHB(OS)

AV =∆VSENSE

∆VITHB

LT4276

4276fa

For more information www.linear.com/LT4276

OVERVIEW

Power over Ethernet (PoE) continues to gain popularity

as products take advantage of DC power and high speed

data available from a single RJ45 connector. The LT4276A

allows higher power while maintaining backwards compat-

ibility with existing PSE systems. The LT4276 combines

a PoE PD controller and a switching regulator controller

capable of either flyback or forward isolated power sup-

ply operation.

SIGNIFICANT DIFFERENCES FROM PREVIOUS

PRODUCTS

The LT4276 has several significant differences from pre-

vious Linear Technology products. These differences are

briefly summarized below. See Applications Information

for more detail.

ITHB Is Inverted from the Usual ITH pin

The ITHB pin voltage has an inverse relationship to the cur-

rent sense comparator threshold, VSENSE. Furthermore, the

ITHB pin offset voltage, VITHB(OS), is 3.17V. See Figure 1.

Duty-Cycle Based Soft-Start

The LT4276 uses a duty cycle ramp soft-start that injects

charge into ITHB. This allows startup without appreciable

overshoot and with inexpensive external components.

The Feedback Pin (FB31) is 3.17V rather than 1.25V

The error amp feedback voltage (VFB) is 3.17V.

applicaTions inForMaTion

Figure 1. VSENSE vs. VITHB

Flyback/Forward Mode Is Pin Selectable

The LT4276 operates in flyback mode if FFSDLY is pulled

down by a resistor to GND. It operates in forward mode

if FFSDLY is pulled up by a resistor to VCC. The value of

this resistor determines the tPGDELAY and tPGSG.

T2P Pin Polarity Is Reversed

The T2P pin pulls up to VCC when active rather than pull-

ing down to GND.

VCC Is Powered by Internally Driven Buck Regulator

The LT4276 includes a buck regulator controller that must

be used to generate the VCC supply voltage.

PoE MODES OF OPERATION

The LT4276 has several modes of operation, depending

on the input voltage sequence applied to the VPORT pin.

VSENSE

∆VSENSE

∆VITHB

VITHB

VITHB(OS)

4276 F01

Table 1. Classification Codes, Power Levels and Resistor Selection

CLASS

PD POWER

AVAILABLE PD TYPE

NOMINAL CLASS

CURRENT

LT4276 GRADE CAPABILITY RESISTOR (1%)

A B C RCLS RCLS++

0 13W Type 1 0.7mA √ √ √ Open Open

1 3.84W Type 1 10.5mA √ √ √ 150Ω Open

2 6.49W Type 1 18.5mA √ √ √ 80.6Ω Open

3 13W Type 1 28mA √ √ √ 52.3Ω Open

4 25.5W Type 2 40mA √ √ 35.7Ω Open

4* 38.7W LTPoE++ 40mA √Open 35.7Ω

4* 52.7W LTPoE++ 40mA √150Ω 47.5Ω

4* 70W LTPoE++ 40mA √80.6Ω 64.9Ω

4* 90W LTPoE++ 40mA √52.3Ω 118Ω

*An LTPoE++ PD classifies as class 4 by an IEEE 802.3 compliant PSE.

LT4276

4276fa

For more information www.linear.com/LT4276

Figure 2. Type 1 Detect/Class Signaling Waveform

Figure 3. Type 2 Detect/Class Signaling Waveform

Figure 4. LTPoE++ Detect/Class Signaling Waveform

applicaTions inForMaTion

Detection

During detection, the PSE looks for a 25kΩ signature

resistor which identifies the device as a PD. The LT4276

signature resistor is smaller than 25k to compensate for

the additional series resistance introduced by the IEEE

required bridge.

Classification

The detection/classification process varies depending on

whether the PSE is Type 1, Type 2, or LTPoE++. A Type 1

PSE, after a successful detection, may apply a classifica-

tion probe voltage of 15.5V to 20.5V and measure current.

In 2-event classification, a Type 2 PSE probes for power

classification twice as shown in Figure 3. The LT4276A or

LT4276B recognizes this and pulls the T2P pin up to VCC to

signal the load that Type 2 power is available. Otherwise it

does not pull up on the T2P pin, indicating that only Type

1 power is available. If an LT4276A senses an LTPoE++

PSE it alternates between pulling T2P up and floating T2P

at a rate of fT2P to indicate the LTPoE++ power is available.

LTPoE++ Classification

The LT4276A allows higher power allocation while main-

taining backwards compatibility with existing PSE systems

by extending the classification signaling of IEEE 802.3.

Linear Technology PSE controllers capable of LTPoE++

are listed in the Related Parts section. IEEE PSEs classify

an LTPoE++ PD as a Type 2 PD.

Classification Resistors (RCLS and RCLS++)

The RCLS and RCLS++ resistors set the classification cur-

rent corresponding to the PD power classification. Select

the value of RCLS from Table 1 and connect the resistor

between the RCLASS pin and GND. For LTPoE++, use

the LT4276A and select the value of RCLS++ from Table

1 in addition to RCLS. The resistor tolerance must be 1%

or better to avoid degrading the overall accuracy of the

classification circuit.

Signature Corrupt During Mark

During the mark state, the LT4276 presents <11kΩ to the

port as required by the IEEE specification.

4276 F02

VPORT

VHSON

VHSOFF

VCLASSMIN

VSIGMAX

VSIGMIN

VRESET

DETECT

CLASS

POWER ON

4276 F03

VPORT

VHSON

VHSOFF

VCLASSMIN

VSIGMAX

VSIGMIN

VRESET

DETECT

1ST CLASS

1ST MARK 2ND MARK

2ND CLASS

POWER ON

4276 F04

VPORT

VHSON

VHSOFF

VCLASSMIN

VSIGMAX

VSIGMIN

VRESET

DETECT

1ST CLASS

1ST MARK 2ND MARK 3RD MARK

2ND CLASS 3RD CLASS

POWER ON

LT4276

4276fa

For more information www.linear.com/LT4276

applicaTions inForMaTion

Inrush and Powered On

Once the PSE detects and optionally classifies the PD, the

PSE then powers on the PD. When the port voltage rises

above the VHSON threshold, it begins to source IGPU out

of the HSGATE pin. This current flows into an external

capacitor (CGATE in Figure 5) that causes a voltage to ramp

up the gate of the external MOSFET. The external MOSFET

acts as a source follower and ramps the voltage up on

the output bulk capacitor (CPORT in Figure 5), thereby

determining the inrush current (IINRUSH in Figure 5). To

meet IEEE requirements, design IINRUSH to be ~100mA.

The LT4276 internal charge pump provides an N-channel

MOSFET solution, eliminating a larger and more costly

P-channel FET. The low RDS(ON) MOSFET also maximizes

power delivery and efficiency, reduces power and heat

dissipation, and eases thermal design.

Figure 5. Programming IINRUSH

Figure 6. VCC Buck Regulator

EXTERNAL VCC SUPPLY

The external VCC supply must be configured as a buck

regulator shown in Figure 6. To optimize the buck regulator,

use the external component values in Table 2 correspond-

ing to the VIN operating range. This buck regulator runs

in discontinuous mode with the inductor peak current

considerably higher than average load current on VCC.

Thus, the saturation current rating of the inductor must

exceed the values shown in Table 2. Place the capacitor, C,

as close as possible to VCC pin 21 and GND pin 19. For

optimal performance, place the external components as

close as possible to the LT4276.

LT4276

HSGATE

GND

4276 F05

VPORT HSSRC

CGATE

IGPU

3.3k

CPORT

VPORT

IINRUSH

IINRUSH =IGPU •CPORT

CGATE

DELAY START

After the HSGATE charges up to approximately 7V above

HSSRC, fully enhancing the external Hot Swap MOSFET,

the switching regulator controller operates after a delay

of tSTART. During this delay, the LT4276 draws IMPS from

VPORT to ensure that the PSE does not DC disconnect

the PD due to Maintain Power Signature requirements.

VIN

VCC

VIN

VCC

GND

SWVCC

LT4276

FMMT723

PBSS9110T

L(µH)

C(µF)

4276 F06

AUXILIARY SUPPLY OVERRIDE

If the AUX pin is held above VAUXT, the LT4276 enters

auxiliary power supply override mode. In this mode the

signature resistor is disconnected, classification is dis-

abled, and HSGATE is pulled down. The T2P pin pulls up

to VCC on the LT4276B (or the LT4276A when no RCLS++

resistor is present). The T2P pin alternates between pulling

up and floating at fT2P on the LT4276A when the RCLS++

resistor is present.

The AUX pin allows for setting the auxiliary supply turn on

(VAUXON) and turn off (VAUXOFF) voltage thresholds. The

auxiliary supply hysteresis voltage (VAUXHYS) is set by

sinking current (IAUXH) only when the AUX pin voltage is

Table 2 . Buck Regulator Component Selection

VIN C L ISAT Re

9V-57V

PoE 22µF

10µF 22µH

100µH ≥1.2A

≥300mA 1Ω

20Ω

LT4276

4276fa

For more information www.linear.com/LT4276

applicaTions inForMaTion

Figure 7. AUX Threshold and Hysteresis Calculation

LT4276

GND

4276 F08a

AUX

VAUX

–

R1=VAUXON −VAUXOFF

IAUXH =VAUXHYS

IAUXH

R2 =R1

VAUXOFF

VAUXT −1











R1≥VAUX(MAX) −VAUXT

1.4mA

SWITCHING REGULATOR CONTROLLER OPERATION

The switching regulator controller portion of the LT4276

is a current mode controller capable of implementing

either a flyback or a forward power supply. When used in

flyback mode, no opto-isolator is required for feedback

because the output voltage is sensed via the transformer’s

third winding.

Flyback Mode

The LT4276 is programmed into flyback mode by placing

a resistor RFFSDLY from the FFSDLY pin to GND. This resis-

tor must be in the range of 5.23kΩ to 52.3kΩ. If using a

potentiometer to adjust RFFSDLY, ensure the adjustment

of the potentiometer does not exceed 52.3kΩ.The value

of RFFSDLY determines tPGDELAY according to the following

equations:

PGDELAY

≈2.69ns / kΩ•R

FFSDLY

+30ns

tPGSG ≈20ns

The PG and SG relationships in flyback mode are shown

in Figure 8.

The SG pin must be connected to the secondary side

MOSFET through a gate drive transformer as shown in

Figure 9. Add a Schottky diode from PG to GND as shown

in Figure 9 to prevent PG from going negative.

Figure 8: PG and SG Relationship in Flyback Mode

Figure 9: Example PG and SG Connections in Flyback Mode

4276 F07

tPGDELAY

tPGon

tPGSG

•

••

SGGND

LT4276

4276 F08

FFSDLY

RFFSDLY

ISEN+

ISEN–

Forward Mode

The LT4276 is programmed into forward mode by placing

a resistor RFFSDLY from the FFSDLY pin to VCC. The RFFSDLY

resistor must be in the range of 10.5kΩ to 52.3kΩ. If using

a potentiometer to adjust RFFSDLY ensure the adjustment

of the potentiometer does not exceed 52.3kΩ.

The value of RFFSDLY determines tPGDELAY and tPGSG ac-

cording to the following equations:

tPGDELAY ≈ 7.16ns/kΩ • RFFSDLY + 17ns

tPGSG ≈ 5.60ns/kΩ • RFFSDLY + 7.9ns

The PG and SG relationships in forward mode are shown

in Figure 10.

less than VAUXT. Use the following equations to set VAUXON

and VAUXOFF via R1 and R2 in Figure 7. A capacitor up to

1000pF may be placed between the AUX pin and GND to

improve noise immunity.

VAUXON must be lower than VHSOFF.

LT4276

4276fa

For more information www.linear.com/LT4276

applicaTions inForMaTion

Figure 10: PG and SG relationship in Forward Mode

In forward mode, the SG pin has the correct polarity to

drive the active clamp P-channel MOSFET through a simple

level shifter as shown in Figure 11. Add a Schottky diode

from the PG to GND as shown in Figure 11 to prevent PG

from going negative.

FEEDBACK AMPLIFIER

In the flyback mode, the feedback amplifier senses the

output voltage through the transformer’s third winding as

shown in Figure 12. The amplifier is enabled only during the

fixed interval, tFB, as shown in Figure 13. This eliminates

the opto-isolator in isolated designs, thus greatly improving

the dynamic response and stability over lifetime. Since tFB

is a fixed interval, the time-averaged transconductance,

gm, varies as a function of the user-selected switching

frequency.

4276 F09

tPGDELAY tPGSG

Figure 11: Example PG and SG Connections in Forward Mode

••

VCC

GND

LT4276

4276 F10

FFSDLY

RFFSDLY

ISEN+

ISEN–

–

•

FEEDBACK

FB31 LT4276 THIRD

PRIMARY

4276 F11

SECONDARY

ITHB

ISEN+

ISEN–

RLDCMP

RFB2

VIN

VOUT

RSENSE

VFB

RFB1

RLDCMP

AV = 10

Figure 12: Feedback and Load Compensation Connection

Figure 13: Feedback Amplifier Timing Diagram

FB31

VOLTAGE GND

4276 F09

tFB

tFBDLY

VFB

FEEDBACK AMPLIFIER OUTPUT, ITHB

As shown in the Block Diagram, VSENSE is the input of

the Current Sense Comparator. VSENSE is derived from

the output of a linear amplifier whose input is the voltage

on the ITHB pin, VITHB.

This linear amplifier inverts its input, VITHB, with a gain,

ΔVSENSE/ΔVITHB, and with an offset voltage of VITHB(OS)

to yield its output, VSENSE. This relationship is shown

graphically in Figure 1. Note the slope ΔVSENSE/ΔVITHB

is a negative number and is provided in the electrical

characteristics table.

VITHB =VITHB(OS) +VSENSE •ΔVSENSE

ΔVITHB

⎛

⎝

⎜⎞

⎠

⎟

–1

LT4276

4276fa

For more information www.linear.com/LT4276

The block diagram shows VSENSE is compared against

the voltage across the current sense resistor, V(ISEN+)-

V(ISEN–) modified by the internal slope compensation

voltage discussed subsequently.

LOAD COMPENSATION

As can be seen in Figure 13, the voltage on the FB31 pin

droops slightly during the flyback period. This is mostly

caused by resistances of components of the secondary

side such as: the secondary winding, RDS(ON) of the syn-

chronous MOSFET, ESR of the output capacitor, etc. These

resistances cause a feedback error that is proportional to

the current in the secondary loop at the time of feedback

sample window. To compensate for this error, the LT4276

places a voltage proportional to the peak current in the

primary winding on the RLDCMP pin.

Determining Feedback and Load Compensation

Resistors

Because the resistances of components on the secondary

side are generally not well known, an empirical method

must be used to determine the feedback and load com-

pensation resistor values.

INITIALLY SET R

FB2

=2kΩ

RFB1 ≈RFB2

VOUT

NTHIRD

SECONDARY

–RFB2

Connect the resistor RLDCMP between the RLDCMP pin and

GND. RLDCMP must be at least 10kΩ. Adjust RLDCMP for

minimum change of VOUT over the full input and output load

range. A potentiometer in series with 10kΩ may be initially

used for RLDCMP and adjusted. The potentiometer+10kΩ

may then be removed, measured, and replaced with the

equivalent fixed resistor. The resulting VOUT differs from

the desired VOUT due to offset injected by load compensa-

tion. The change to RFB2 to correct this is predicted by:

ΔRFB2 =ΔVOUT

NTHIRD

SECONDARY

RFB22

FB1

applicaTions inForMaTion

Where: ΔVOUT is the desired change to VOUT

ΔRFB2 is the required change to RFB2

NTHIRD/NSECONDARY is the transformer third

winding to secondary winding

OPTO-ISOLATOR FEEDBACK

For forward mode operation, the flyback voltage cannot be

sensed across the transformer. Thus, opto-isolator feed-

back must be used. When using opto-isolator feedback,

connect the FB31 pin to GND and leave the RLDCMP pin

open. In this condition, the feedback amplifier sinks an

average current of ISINK into the ITHB pin. An example for

feedback connections is shown in Figure 14. Note that

since ISINK is time-averaged over the switching period,

the sink current varies as a function of the user-selected

switching frequency.

Figure 14: Opto-isolator Feedback

Connections in the Forward Mode

LT4276

ITHB

4276 F13

VCC VOUT

FB31GND

SOFT-START

In PoE applications, a proper soft-start design is required

to prevent the PD from drawing more current than the

PSE can provide.

The soft-start time, tSFST, is approximately the time in

which the power supply output voltage, VOUT, is charg-

ing its output capacitance, COUT. This results in an inrush

current at the port of the PD, Iport_inrush. Care must be

taken in selecting tSFST to prevent the PD from drawing

more current than the PSE can provide.

LT4276

4276fa

For more information www.linear.com/LT4276

applicaTions inForMaTion

In the absence of an output load current, the Iport_inrush,

is approximated by the following equation:

Iport_inrush ≈ (COUT • VOUT2)/(η • tSFST • VIN)

where η is the power supply efficiency,

VIN is the input voltage of the PD

Iport_inrush plus the port current due to the load current

must be below the current the PSE can provide. Note that

the PSE current capability depends on the PSE operating

standard.

The LT4276 contains a soft-start function that controls

tSFST by connecting an external capacitor, CSFST, between

the SFST pin and GND. The SFST pin is pulled up with ISFST

when the LT4276 begins switching. The voltage ramp on

the SFST pin is proportional to the duty cycle ramp for PG.

For flyback mode, the soft-start time is:

tSFST =600µA

CSFST

ISFST

⎛

⎝

⎜⎞

⎠

⎟tPGon +tPGDELAY – tMIN

( )

where tPGon is the time when PG is high as shown in

Figure 8 once the power supply is in steady-state.

In forward mode, each of the back page applications sche-

matics provides a chart with tSFST vs. CSFST. Select the

application and choose a value of CSFST that corresponds

to the desired soft-start time.

CURRENT SENSE COMPARATOR

The LT4276 uses a differential current sense comparator

to reduce the effects of stray resistance and inductance

on the measurement of the primary current. ISEN+ and

ISEN– must be Kelvin connected to the sense resistor pads.

Like most switching regulator controllers, the current

sense comparator begins sensing the current tMIN after

PG turns on. Then, the comparator turns PG off after the

voltage across ISEN+ and ISEN– exceeds the current

sense comparator threshold, VSENSE. Note that the voltage

across ISEN+ and ISEN– is modified by LT4276’s internal

slope compensation.

SLOPE COMPENSATION

The LT4276 incorporates current slope compensation.

Slope compensation is required to ensure current loop

stability when the duty cycle is greater than or near 50%.

The slope compensation of the LT4276 does not reduce

the maximum peak current at higher duty cycles.

CONTROL LOOP COMPENSATION

In flyback mode, loop frequency compensation is per-

formed by connecting a resistor/capacitor network from

the output of the feedback amplifier (ITHB pin) to GND as

shown in Figure 12. In forward mode, loop compensation

is performed by varying RX and CX in Figure 14.

ADJUSTABLE SWITCHING FREQUENCY

The LT4276 has a default switching frequency, fOSC, of 214

kHz when the ROSC pin is left open. If a higher switching

frequency, fSW, is desired (up to 300 kHz), a resistor no

smaller than 45.3kΩ may be added between the ROSC pin

to GND. The resistor can be calculated below:

ROSC =

3900kΩ•kHz

fSW – fOSC

( )

kΩ

( )

SHORT CIRCUIT RESPONSE

If the power supply output voltage is shorted, overloaded,

or if the soft-start capacitor is too small, an overcurrent

fault event occurs when the voltage across the sense pins

exceeds VFAULT (after the blanking period of tMIN). This

begins the internal fault timer tFAULT. For the duration

of tFAULT, the LT4276 turns off PG and SG and pulls the

SFST pin to GND. After tFAULT expires, the LT4276 initi-

ates soft-start.

The fault and soft-start sequence repeats as long as the

short circuit or overload conditions persist. This condition

is recognized by the PG waveform shown in Figure 15

re peating at an interval of tFAULT.

Figure 15: PG Waveform with Output Shorted

tFAULT

4276 F14

LT4276

4276fa

For more information www.linear.com/LT4276

applicaTions inForMaTion

OVERTEMPERATURE PROTECTION

The IEEE 802.3 specification requires a PD to withstand

any applied voltage from 0V to 57V indefinitely. During

classification, however, the power dissipation in the LT4276

may be as high as 1.5W. The LT4276 can easily tolerate

this power for the maximum IEEE classification timing but

overheats if this condition persists abnormally.

The LT4276 includes an over-temperature protection

feature which is intended to protect the device during

momentary overload conditions. If the junction temperature

exceeds the over-temperature threshold, the LT4276 pulls

down HSGATE pin, disables classification, and disables

the switching regulator operation.

MAXIMUM DUTY CYCLE

The maximum duty cycle of the PG pin is modified by the

chosen tPGDELAY and fSW. It is calculated below:

MAX POWER SUPPLY DUTY CYCLE

=DMAX – tPGDELAY •fSW

For an appropriate margin during transient operation, the

forward or flyback power supply should be designed so

that its maximum steady-state duty cycle should be about

10% lower than the LT4276 Maximum Power Supply Duty

Cycle calculated above.

EXTERNAL INTERFACE AND COMPONENT SELECTION

PoE Input Diode Bridge

PDs are required to polarity-correct its input voltage.

When diode bridges are used, the diode forward voltage

drops affect the voltage at the VPORT pin. The LT4276

is designed to tolerate these voltage drops. The voltage

parameters shown in the Electrical Characteristics are

specified at the LT4276 package pins.

For high efficiency applications, the LT4276 supports

an LT4321-based PoE ideal diode bridge that reduces

the forward voltage drop from 0.7V to nearly 20mV per

diode in normal operation, while maintaining IEEE 802.3

compliance.

Auxiliary Input Diode Bridge

Some PDs are required to receive AC or DC power from an

auxiliary power source. A diode bridge is typically required

to handle the voltage rectification and polarity correction.

In high efficiency applications, the voltage drop across the

rectifier cannot be tolerated. The LT4276 can be configured

with an LT4320-based ideal diode bridge to recover the

diode voltage drop and ease thermal design.

Input Capacitor

A 0.1µF capacitor is needed from VPORT to GND to meet

the input impedance requirement in IEEE 802.3 and to

properly bypass the LT4276. This capacitor must be placed

as close as possible to the VPORT and GND pins.

Transient Voltage Suppressor

The LT4276 specifies an absolute maximum voltage of

100V and is designed to tolerate brief overvoltage events

due to Ethernet cable surges.

To protect the LT4276, install a unidirectional transient

voltage suppressor (TVS) such as an SMAJ58A between

the VPORT and GND pins. This TVS must be placed as close

as possible to the VPORT and GND pins of the LT4276.

For PD applications that require an auxiliary power input,

install a TVS between VIN and GND as close as possible

to the LT4276.

For extremely high cable discharge and surge protection

contact Linear Technology Applications.

LT4276

4276fa

For more information www.linear.com/LT4276

Typical applicaTions

+VOUT

5V AT 2.3A

–VOUT

L1: COILCRAFT, DO1813P-181HC

L2: COILCRAFT, DO1608C-103

L4: COILCRAFT, DO1608C-104

C2: 22µF, 6.3V, MURATA GRM31CR70J226KE19

C5: 47µF, 6.3V, PANASONIC 6SVP47M

C7: 2.2µF, 100V, MURATA GRM32ER72A225KA35

T1: WÜRTH, 750313109

Q1: PSMN075-100MSE

T2: PCA EPA4271GE OR PULSE PE-68386NL

VPORT

GND

10µH L1

180nH

100µH

10µF

100V

10nF

100V

3.3k

10µF

10V

HSSRC SWVCC FB31

ITHBROSCSFSTFFSDLYRCLASSGND

VPORT

LT4276C

HSGATE

ISEN+

ISEN–

VIN VCC

2.2µF

FDN86246

BAT54WS

BAT46WS

4276 TA02

PSMN4R2-30MLD

MMBT3906 MMBT3904

1nF

1µF

6.04k

20Ω

270Ω

1/4W

11Ω

1/4W

60mΩ

1/4W

15Ω

100Ω

1µF

330pF

0.1µF

107k5.23k52.3Ω

8.2Ω

PTVS58VP1UTP

4.7nF

2.2nF

2KV

20k

10k

2.2nF

22µF C5

47µF

6.3V

47pF

630V

0.1µF

100V

2.2nF

2kV

BAV19WS

••

•

FMMT723

13W (TYPE 1) PoE Power Supply in Flyback Mode with 5V, 2.3A Output

Efficiency vs Load Current Output Regulation vs Load Current

LOAD CURRENT (A)

0.2

EFFICIENCY (%)

1.21.0 1.6 1.8 2.0 2.21.4 2.40.4 0.80.6

4276 TA02a

VPORT = 37V

VPORT = 48V

VPORT = 57V

LOAD CURRENT (A)

0.2

4.80

VOUT (V)

5.15

5.10

5.05

5.00

4.95

4.90

4.85

5.20

1.21.0 1.6 1.8 2.0 2.21.4 2.40.4 0.80.6

4276 TA02b

VPORT = 37V

VPORT = 48V

VPORT = 57V

LT4276

4276fa

For more information www.linear.com/LT4276

Typical applicaTions

+VOUT

5V AT 4.7A

–VOUT

L1: COILCRAFT, DO1813P-181HC

L2: COILCRAFT, DO1608C-103

L4: COILCRAFT, DO1608C-104

C2, C3: 22µF, 6.3V, MURATA GRM31CR70J226KE19

C5: 47µF, 6.3V, PANASONIC 6SVP47M

C7: 2.2µF, 100V, MURATA GRM32ER72A225KA35

T1: WÜRTH, 750313082 OR PCA EPC3409G

Q1-Q9: PSMN075-100MSE

T2: PCA EPA4271GE OR PULSE PE-68386NLL2

10µH L1

180nH

100µH

10µF

100V

10nF

100V

3.3k

24V

8.2Ω

10µF

10V

HSSRC

SWVCC FB31

T2P

ITHBROSCSFSTFFSDLYRCLASSGND

VPORT

LT4276B

HSGATE

ISEN+

ISEN–

VIN VCC

2.2µF

BSZ520N15NS3G

BAT54WS

BAT46WS

TO MICROPROCESSOR

4276 TA03

PSMN2R4-30MLD

MMBT3906 MMBT3904

1nF

1µF

5.90k20Ω

160Ω||160Ω

1/4W

5.1Ω

1/4W

40mΩ

1/4W

15Ω

100Ω

1µF

220pF

0.1µF

107k7.50k35.7Ω

PTVS58VP1UTP 3.3nF

2.2nF

2KV

20k

10k

2.2nF

C2, C3

22µF||22µF C5

47µF

100pF

100V

47nF

100V

2.2nF

2kV

OPTO

BG36

LT4321

BG12TG12 TG36

TG78TG45BG45 BG78

OUTP

OUTN

IN12

Q2 Q3

Q4 Q5

Q6 Q7

Q8 Q9

DATA

PAIRS

SPARE

PAIRS

IN36

IN45

IN78

47nF

100V

BAV19WS

••

•

FMMT723

25.5W (Type 2) PoE+ Power Supply in Flyback Mode with 5V, 4.7A Output

Efficiency vs Load Current VOUT vs Load Current

LOAD CURRENT (A)

0.5

EFFICIENCY (%)

2.01.5 3.0 3.5 4.0 4.52.5 5.01.0

4276 TA03a

VPORT = 42.5V

VPORT = 50V

VPORT = 57V

LOAD CURRENT (A)

0.5

4.80

VOUT (V)

5.15

5.10

5.05

5.00

4.95

4.90

4.85

5.20

2.01.5 3.0 3.5 4.0 4.52.5 5.01.0

4276 TA03b

VPORT = 42.5V

VPORT = 50V

VPORT = 57V

LT4276

4276fa

For more information www.linear.com/LT4276

Typical applicaTions

10nF

100V

3.3k

100µH

10µF

10V

BAV19WS

FMMT723

8.2Ω

PTVS58VP1UTP

0.1µF

100V

2.2µH

100µF

(×2)

100µF

6HVA100M

4.9µH

22µF

100V

HSSRC SWVCC FFSDLY

ITHBROSCSFSTRCLASS++

RCLASSGND FB31

T2P

VPORT

LT4276A

HSGATE

ISEN+

ISEN–

VIN VCC

VCC

+VOUT

+5V AT

13A

VCC

2.2µF

(×2)

BAT54WS

BSC190N12NS3

4276 TA04

20m

1/4W

100Ω

1206

10nF

250V

5Ω

100nF

250V

750Ω

330Ω 240Ω

4.7n

ZR431

10k 10.0k

10.0k

10Ω

CMMSH1-40L BSC054N04NSBSC054N04NS

CMMSH1-40L

8.2V

CMHZ4694

18V

CMHZ5248B

18V

CMHZ5248B

2.2nF

2kV

33nF

0.1µF

10k

0.1µF FDMC2523P

CMMSH1-40L

M0C207M

MMBT3904

VPORT

GND

13k

20Ω

80.6Ω 64.9Ω

0.47µF 100pF

100k

107k

••

L1: COILCRAFT, XAL-1010-222ME

L2: WÜRTH, 744314490

L4: COILCRAFT, DO1608C-104

C5, 100µF, 6.3V, SUNCON 6HVA100M

C7: 2.2µF, 100V, MURATA GRM32ER72A225KA35L

C8: 100µF, 6.3V, SUNCON 6HVA100M

T1: WÜRTH, 750313095

Q1: PSMN040-100MSE

TO MICROPROCESSOROPTO

10nF

Efficiency vs Load Current VOUT vs Load Current

70W LTPoE++ Power Supply in Forward Mode with 5V, 13A Output

LOAD CURRENT (A)

EFFICIENCY (%)

76 9 10 11 128 1332 54

4276 TA04a

VPORT = 41V

VPORT = 50V

VPORT = 57V

LOAD CURRENT (A)

4.80

VOUT (V)

5.15

5.10

5.05

5.00

4.95

4.90

4.85

5.20

76543 9 10 11 128 132

4276 TA04b

VPORT = 41V

VPORT = 50V

VPORT = 57V

CSFST (µF) tSFST (ms)

0.10 1.2

0.33 3.8

1.0 12

3.3 38

LT4276

4276fa

For more information www.linear.com/LT4276

Efficiency vs Load Current VOUT vs Load Current

6.5µH

22µF

100V

HSSRC

SWVCC FFSDLY

ITHBROSCSFSTRCLASS++

RCLASSGND FB31

T2P

VPORT

LT4276A

HSGATE

ISEN+

ISEN–

VIN VCC

VCC

+VOUT

+12V AT

VCC

2.2µF

(×2)

BAT54WS

BSC190N12NS3

4276 TA05

15mΩ

1/4W

100Ω

1206

33nF

250V

0.22µF

250V

750Ω

820Ω 20k

ZR431

10k

10.0k

100pF

38.3k

13k

10Ω

CMMSH1-60

BSC123N08S3

CMMSH1-100

13V

CMHZ4700

7.5V

CMHZ5236B

2.2nF

2kV

6.8nF

0.1µF

10k

0.1µF FDMC2523P

CMMSH1-40L

M0C207M

MMBT3904

29.4k

VCC

BG36

LT4321

BG12TG12 TG36

TG78TG45BG45 BG78

OUTP

OUTN

IN12

Q2 Q3

Q4 Q5

Q6 Q7

Q8 Q9

DATA

PAIRS

SPARE

PAIRS

IN36

IN45

IN78

76.8Ω 64.9Ω

1µF 100pF*

100pF

100k

107k 330pF

20Ω ••

7.5Ω

10nF

100V

47nF

100V

3.3k

100µH

10µF

10V

8.2Ω

PTVS58VP1UTP

47nF

100V

8.2µH

22µF

16V

(×2)

100µF

16V

16HVA100M

L1: COILCRAFT, XAL-1010-822ME

L2: WÜRTH, 744314650

L4: COILCRAFT, DO1608C-104

C5, 100µF, 6.3V, TDK C3225X5R0J107M

C7: 2.2µF, 100V, MURATA GRM32ER72A225KA35L

C8: 100µF, 16V, SUNCON 16HVA100M

T1: PCA EPC3577G-LF

T2: WÜRTH, 749022016

Q1: PSMN040-100MSE

Q2-Q9: PSMN075-100MSE

TO MICROPROCESSOROPTO

FMMT723 820pF 100pF

+VOUT

7.5V

CMHZ5236B

5.1k

FMMT624

5.1k

100pF

BAV19WS

Typical applicaTions

90W LTPoE++ Power Supply in Forward Mode with 12V, 7A Output

LOAD CURRENT (A)

0.7

EFFICIENCY (%)

2.82.1 4.2 4.9 5.6 6.33.5 7.01.4

4276 TA05a

VPORT = 41V

VPORT = 50V

VPORT = 57V

LOAD CURRENT (A)

0.7

11.5

VOUT (V)

12.4

12.3

12.2

12.1

12.0

11.9

11.8

11.7

11.6

12.5

2.82.11.4 4.2 4.9 5.6 6.33.5 7.0

4276 TA05b

VPORT = 41V

VPORT = 50V

VPORT = 57V

CSFST (µF) tSFST (ms)

0.10 1.5

0.33 4.9

1.0 15

3.3 48

LT4276

4276fa

For more information www.linear.com/LT4276

Typical applicaTions

38.7W LTPoE++ Power Supply in Flyback Mode with 5V, 7A Output

VOUT

5V AT 7A

–VOUT

L1: COILCRAFT, DO1813P-181HC

L2: COILCRAFT, DO1608C-103

L4: COILCRAFT, DO1608C-104

C2, C3: 47µF, 6.3V, GRM31CR60J476ME19L

C5: 47µF, 6.3V, PANASONIC 6SVP47M

C7: 2.2µF, 100V, MURATA GRM32ER72A225KA35L

T1: WÜRTH, 750314783 OR PCA EPC3586G

Q1-Q9: PSMN075-100MSE

T2: PCA EPA4271GE OR PULSE PE-68386NLL2

10µH L1

180nH

100µH

10µF

100V

10nF

100V

47nF

100V

3.3k

24V

8.2Ω

10µF

10V

HSSRC

SWVCC FB31

T2P

ITHBROSCSFSTFFSDLYRCLASS++

GND

VPORT

LT4276A

HSGATE

ISEN+

ISEN–

VIN VCC

2.2µF

BSZ900N20

NS3G

BAT54WS

BAT46WS

TO MICROPROCESSOR

4276 TA06

PSMN2R4-30MLD

MMBT3906 MMBT3904

1nF

1µF

5.90k

2.00kΩ

80Ω

1/4W

5.1Ω

1/4W

40mΩ

1/4W

15Ω

100Ω

20Ω

1µF

220pF

0.1µF

107k7.50k

RLDCMP

51k35.7Ω

PTVS58VP1UTP 3.3nF

2.2nF

2KV

20k

10k

2.2nF

C2, C3

47µF||47µF C5

47µF

100pF

100V

47µF

100V

2.2nF

2kV

OPTO

BG36

LT4321

BG12TG12 TG36

TG78TG45BG45 BG78

OUTP

OUTN

IN12

Q2 Q3

Q4 Q5

Q6 Q7

Q8 Q9

DATA

PAIRS

SPARE

PAIRS

IN36

IN45

IN78

BAV19WS

••

•

FMMT723

Efficiency vs Load Current

Output Regulation

vs Load Current

LOAD CURRENT (A)

0.5

EFFICIENCY (%)

4.03.5 5.0 5.5 6.0 6.54.5 7.03.02.52.01.51.0

4276 TA06a

VPORT = 50V

VPORT = 57V

LOAD CURRENT (A)

0.5

4.80

VOUT (V)

5.15

5.10

5.05

5.00

4.95

4.90

4.85

5.20

4.03.5 5.0 5.5 6.0 6.54.5 7.03.02.52.01.51.0

4276 TA06b

VPORT = 50V

VPORT = 57V

LT4276

4276fa

For more information www.linear.com/LT4276

Typical applicaTions

25.5W (Type 2) PoE+ and 9V-57V Auxiliary Input Power Supply in Flyback Mode with 12V, 1.9A Output

Efficiency vs Load Current

Output Regulation

vs Load Current

VOUT

12V AT 1.9A

–VOUT

L1: COILCRAFT, DO1813P-561ML

L2: WÜRTH, 7443330820

L3: MURATA, LQM31PN2R2M00L

L4: COILCRAFT, DO1813H-223

C2, C3: 10µF, 16V, MURATA GRM31CR61C106KA88

C5: 33µF, 20V, KEMET, T494V336M020AS

C7, C8: 3.3µF, 100V, TDK C3225X7S2A335M

T1: PCA EPC3601G OR WÜRTH 750315422

Q1: PSMN075-100MSE

Q1-Q9:PSMN075-100MSE

T2: PCA EPA4271GE OR PULSE PE-68386NL

8.2µH

2.2µH

1µF

680µF

63V

560nH

22µH

10µF

100V

68nF

100V

0.1µF

3.3k 158k

931k

24V

47nF

100V

8.2Ω

22µF

10V

PMEG10010ELR

HSSRC

SWVCC FB31

T2P

ITHBROSCSFSTFFSDLYRCLASSGND

VPORT

AUX

LT4276B

HSGATE

ISEN+

ISEN–

VIN VCC

C7, C8

3.3µF

FDMC86160

BAT54WS

BAT46WS

TO MICROPROCESSOR

4276 TA08

BSZ900NF20NS3

CMLT7820G CMLT3820G

220pF

1µF

4.75k

2.00k

62Ω

1/4W

82Ω||82Ω

1/4W

15mΩ

1/4W

15Ω

100Ω

1µF

220pF

0.1µF

107k9.31k

RLDCMP

51k35.7Ω

PTVS58VP1UTP

4.7nF

2.2nF

2KV

43k

10k

2.2nF

C2, C3

10µF||10µF C5

33µF

100pF

100V

47nF

100V

2.2nF

2kV

OPTO

BG36

LT4321

BG12TG12 TG36

TG78TG45BG45 BG78

OUTP

OUTN

IN12

TG2

TG1 OUTP

OUTN

IN1

IN2

BG2

BG1

Q2 Q3

Q4 Q5

Q6 Q7

Q8 Q9

DATA

PAIRS

SPARE

PAIRS

IN36

IN45

IN78

LT4320

BSZ110N06NS3 x4

MMSD4148 x3

VAUX

9V TO 57VDC

OR 24VAC

1Ω

••

•

FMMT723

LOAD CURRENT (A)

0.2

EFFICIENCY (%)

1.2 1.6 1.81.4 2.01.00.80.60.4

4276 TA08a

VAUX = 57V

VAUX = 42.5V

VAUX = 24V

VAUX = 9V

LOAD CURRENT (A)

0.2

11.5

VOUT (V)

12.4

12.3

12.2

12.1

12.0

11.9

11.8

11.7

11.6

12.5

1.2 1.6 1.81.4 2.01.00.80.60.4

4276 TA08b

VAUX = 57V

VAUX = 42.5V

VAUX = 24V

VAUX = 9V

LT4276

4276fa

For more information www.linear.com/LT4276

Typical applicaTions

25.5W (Type 2) PoE+ Power Supply in Flyback Mode with 3.3V, 6.8A Output

Efficiency vs Load Current

Output Regulation

vs Load Current

+VOUT

3.3V AT 6.8A

–VOUT

L1: COILCRAFT, DO1813P-181HC

L2: COILCRAFT, DO1608C-103

L4: COILCRAFT, DO1608C-104

C2, C3: 22µF, 6.3V, MURATA GRM31CR70J226KE19

C5: 68µF, 4V, 4SVPA68MAA

C7: 2.2µF, 100V, MURATA GRM32ER72A225KA35

T1: WÜRTH, 750310743 OR PCA EPC3408G

Q1-Q9: PSMN075-100MSE

T2: PCA EPA4271GE OR PULSE PE-68386NLL2

10µH L1

180nH

100µH

10µF

100V

10nF

100V

47nF

100V

3.3k

24V

8.2Ω

10µF

10V

HSSRC

SWVCC FB31

T2P

ITHBROSCSFSTFFSDLYRCLASSGND

VPORT

LT4276B

HSGATE

ISEN+

ISEN–

VIN VCC

2.2µF

BSZ900N20NS3

BAT54WS

BAT46WS

TO MICROPROCESSOR

4276 TA09

PSMN2R4-30MLD

MMBT3906 MMBT3904

1nF

47Ω

1µF

6.49k

100Ω

1/4W

5.1Ω

1/4W

40mΩ

1/4W

15Ω

100Ω

1µF

470pF

0.1µF

107k6.81k35.7Ω

PTVS58VP1UTP 4.7nF

2.2nF

2KV

8.25k

10k

2.2nF

C2, C3

22µF||22µF C5

68µF

100pF

100V

47nF

100V

2.2nF

2kV

OPTO

BG36

LT4321

BG12TG12 TG36

TG78TG45BG45 BG78

OUTP

OUTN

IN12

Q2 Q3

Q4 Q5

Q6 Q7

Q8 Q9

DATA

PAIRS

SPARE

PAIRS

IN36

IN45

IN78

B0540WS

BAV19WS

20Ω

••

•

FMMT723

LOAD CURRENT (A)

0.7

EFFICIENCY (%)

4.2 5.6 6.34.9 7.03.52.82.11.4

4276 TA09a

VPORT = 57V

VPORT = 50V

VPORT = 42.5V

LOAD CURRENT (A)

0.7

3.1

VOUT (V)

3.5

3.4

3.3

3.2

3.6

4.2 5.6 6.34.9 7.03.52.82.11.4

4276 TA09b

VPORT = 57V

VPORT = 50V

VPORT = 42.5V

LT4276

4276fa

For more information www.linear.com/LT4276

Typical applicaTions

25.5W (Type 2) PoE+ Power Supply in Flyback Mode with 24V, 1A Output

Efficiency vs Load Current VOUT vs Load Current

VOUT

24V AT 1A

–VOUT

L2: COILCRAFT, DO1608C-103

L4: COILCRAFT, DO1608C-104

C2: 4.7µF, 50V, MURATA GRM31CR71H475M012

C5: 22µF, 35V, PANASONIC EEH-ZA1V220R

C7: 2.2µF, 100V, MURATA GRM32ER72A225KA35

T1: WÜRTH, 750314782 OR PCA EPC3603G

Q1-Q9: PSMN075-100MSE

T2: PCA EPA4271GE OR PULSE PE-68386NL

10µH

100µH

10µF

100V

10nF

100V

3.3k

24V

8.2Ω

10µF

10V

HSSRC

SWVCC FB31

T2P

ITHBROSCSFSTFFSDLYRCLASSGND

VPORT

LT4276B

HSGATE

ISEN+

ISEN–

VIN VCC

2.2µF

BSZ520N15NS3G

BAT54WS

BAT46WS

TO MICROPROCESSOR

4276 TA10

BSZ12DN20NS3

MMBT3906 MMBT3904

150pF

0.1µF

6.49k

2.00kΩ

20Ω

100Ω

1/4W

120Ω||120Ω

1/4W

40mΩ

1/4W

15Ω

100Ω

1µF

10pF

0.47µF

107k5.23k

RLDCMP

24k35.7Ω

PTVS58VP1UTP 3.3nF

2.2nF

2KV

160k

10k

2.2nF

C2, C3

4.7µF

50V

22µF

47pF

100V

47nF

100V

2.2nF

2kV

OPTO

BG36

LT4321

BG12TG12 TG36

TG78TG45BG45 BG78

OUTP

OUTN

IN12

Q2 Q3

Q4 Q5

Q6 Q7

Q8 Q9

DATA

PAIRS

SPARE

PAIRS

IN36

IN45

IN78

47nF

100V

BAV19WS

••

•

FMMT723

LOAD CURRENT (A)

0.1

EFFICIENCY (%)

0.6 0.8 0.90.7 1.00.50.40.30.2

4276 TA10a

VPORT = 57V

VPORT = 50V

VPORT = 42.5V

LOAD CURRENT (A)

0.1

23.0

VOUT (V)

24.6

24.4

24.8

24.2

24.0

23.8

23.6

23.4

23.2

25.0

0.6 0.8 0.90.7 1.00.50.40.30.2

4276 TA10b

VPORT = 57V

VPORT = 50V

VPORT = 42.5V

LT4276

4276fa

For more information www.linear.com/LT4276

package DescripTion

Please refer to http://www.linear.com/product/LT4276#packaging for the most recent package drawings.

4.00 ±0.10

(2 SIDES)

2.50 REF

5.00 ±0.10

(2 SIDES)

NOTE:

1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WXXX-X).

2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

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

MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm 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

TOP MARK

(NOTE 6)

0.40 ±0.10

27 28

BOTTOM VIEW—EXPOSED PAD

3.50 REF

0.75 ±0.05 R = 0.115

TYP

R = 0.05

TYP

PIN 1 NOTCH

R = 0.20 OR 0.35

× 45° CHAMFER

0.25 ±0.05

0.50 BSC

0.200 REF

0.00 – 0.05

(UFD28) QFN 0506 REV B

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED

0.70 ±0.05

0.25 ±0.05

0.50 BSC

2.50 REF

3.50 REF

4.10 ±0.05

5.50 ±0.05

2.65 ±0.05

3.10 ±0.05

4.50 ±0.05

PACKAGE OUTLINE

2.65 ±0.10

3.65 ±0.10

3.65 ±0.05

UFD Package

28-Lead Plastic QFN (4mm × 5mm)

(Reference LTC DWG # 05-08-1712 Rev B)

LT4276

4276fa

For more information www.linear.com/LT4276

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

A 12/15 Changed diode type of diode between SWVCC and VCC from Schottky to regular (BAV19WS) on all applicable

schematics.

Added additional conditions to VAUXT and IAUXH parameters.

Revised graph: PG Delay Time vs Temperature in Flyback Mode.

Added T2 transformer part number recommendation to all flyback schematics.

Updated parts list for 25.5W (12V/1.9A) flyback schematic.

1, 10, 16-20,

22, 23

16, 17, 19-23, 26

LT4276

4276fa

For more information www.linear.com/LT4276

 LINEAR TECHNOLOGY CORPORATION 2015

LT 1215 REV A • PRINTED IN USA

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LT4276

relaTeD parTs

Typical applicaTion

PART NUMBER DESCRIPTION COMMENTS

LTC4267/

LTC4267-1/

LTC4267-3

IEEE 802.3af PD Interface With Integrated

Switching Regulator Internal 100V, 400mA Switch, Programmable Class, 200/300kHz Constant Frequency

PWM

LTC4269-1 IEEE 802.3af PD Interface With Integrated

Flyback Switching Regulator 2-Event Classification, Programmable Class, Synchronous No-Opto Flyback Controller,

50kHz to 250kHz, Aux Support

LTC4269-2 IEEE 802.3af PD Interface With Integrated

Forward Switching Regulator 2-Event Classification, Programmable Class, Synchronous Forward Controller, 100kHz to

500kHz, Aux Support

LT4275A/B/C LTPoE++/PoE+/PoE PD Controller External Switch, LTPoE++ Support

LTC4278 IEEE 802.3af PD Interface With Integrated

Flyback Switching Regulator 2-Event Classification, Programmable Class, Synchronous No-Opto Flyback Controller,

50kHz to 250kHz, 12V Aux Support

LTC4290/LTC4271 8-Port PoE/PoE+/LTPoE++ PSE Controller Transformer Isolation, Supports IEEE 802.3af, IEEE 802.3at and LTPoE++ PDs

LT4320/LT4320-1 Ideal Diode Bridge Controller 9V-72V ,DC to 600Hz Input. Controls 4-NMOSFETs, Voltage Rectification without Diode Drops

LT4321 PoE Ideal Diode Bridge Controller Controls 8-NMOSFETs for IEEE-required PD Voltage Rectification without Diode Drops

25.5W (Type 2) PoE+ Power Supply in Flyback Mode with 12V, 1.9A Output

Efficiency vs Load Current Output Regulation vs Load Current

OUT

12V AT 1.9A

–V

OUT

C5: 22µF, 16V, PANASONIC 16SVP22M

C7: 2.2µF, 100V, MURATA GRM32ER72A225KA35

T1: WÜRTH, 750310742 OR PCA EPC3410G

Q1-Q9: PSMN075-100MSE

T2: PCA EPA4271GE OR PULSE PE-68386NL

10µH L1

180nH

100µH

10µF

100V

10nF

100V

3.3k

24V

8.2Ω

10µF

10V

HSSRC

SWVCC FB31

T2P

ITHBROSCSFSTFFSDLYRCLASSGND

VPORT

LT4276B

HSGATE

ISEN+

ISEN–

2.2µF

BSZ520N15NS3G

BAT54WS

BAT46WS

MOC207M

OUT

TO MICROPROCESSOR

4276 TA11

FDMC86160

MMBT3906 MMBT3904

470pF

1µF

6.49k

2.00kΩ

150V

1/4W

13Ω

1/4W

40mΩ

1/4W

15Ω

100Ω

1µF

220pF

0.1µF

107k5.23k35.7Ω

PTVS58VP1UTP 3.3nF

2.2nF

2KV

26.1k

10k

2.2nF

10µF C5

22µF

47pF

630V

47nF

100V

2.2nF

2kV

BG36

LT4321

BG12TG12 TG36

TG78TG45BG45 BG78

OUTP

OUTN

IN12

Q2 Q3

Q4 Q5

Q6 Q7

Q8 Q9

DATA

PAIRS

SPARE

PAIRS

IN36

IN45

IN78

47nF

100V

L1: COILCRAFT, DO1813P-181HC

L2: COILCRAFT, DO1608C-103

L4: COILCRAFT, DO1608C-104

C2: 10µF, 16V, MURATA GRM31CR61C106KA88

BAV19WS

10k

47k

20Ω

••

•

FMMT723

LOAD CURRENT (A)

0.2

EFFICIENCY (%)

1.2 1.6 1.81.4 2.01.00.80.60.4

4276 TA11a

VPORT = 57V

VPORT = 50V

VPORT = 42.5V

LOAD CURRENT (A)

0.2

11.5

VOUT (V)

12.3

12.2

12.1

12.0

11.9

11.8

11.7

11.6

12.5

12.4

1.2 1.6 1.81.4 2.01.00.80.60.4

4276 TA11b

VPORT = 57V

VPORT = 50V

VPORT = 42.5V