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LT4275

4275f

Typical applicaTion

FeaTures DescripTion

LTPoE

/PoE

PD Controller

The LT

4275 is a pin-for-pin compatible family of IEEE

802.3 and LTPoE

powered device (PD) controllers.

The LT4275A employs a proprietary LTPoE

classification

scheme, delivering 38.7W, 52.7W, 70W or 90W of power

at the PD RJ45 connector. The LT4275A is fully compat-

ible with IEEE 802.3. The LT4275B is an IEEE 802.3at

compliant, Type 2 (PoE

) PD delivering up to 25.5W. The

LT4275C is an IEEE 802.3af compliant, Type 1 (PoE) PD

delivering up to 13W.

The LT4275 internal charge pump provides an N-channel

MOSFET solution, eliminating a larger and more costly

P-channel MOSFET. A low R

DS(ON)

MOSFET also maxi-

mizes power delivery and efficiency, reduces power and

heat dissipation, and eases thermal design. Startup inrush

current is adjustable with an external capacitor. The LT4275

also includes a power good output, on-board signature

resistor, undervoltage lockout, and thermal protection. The

LT4275A/LT4275B drives a single opto-coupler to indicate

the power level of the attached PSE. Pin-selectable sup-

port for non-standard low voltage operation is provided.

Auxiliary power override is supported with the AUX pin.

The LT4275A can be configured to support all possible

LTPoE

, 802.3at

and 802.3af power levels with external

component changes.

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

LTPoE

and Hot Swap are trademarks of Linear Technology Corporation. All other trademarks

are the property of their respective owners.

LTPoE

90W Powered Device Interface

applicaTions

IEEE 802.3af/at and LTPoE

™ Powered Device

(PD) Controller

LTPoE

Supports Power Levels Up to 90W

LT4275A Supports All of the Following Standards:

LTPoE

38.7W, 52.7W, 70W and 90W

IEEE 802.3at 25.5W Compliant

IEEE 802.3af Up to 13W Compliant

LT4275B is IEEE 802.3at/af Compliant

LT4275C is IEEE 802.3af Compliant

100V Absolute Maximum Input Voltage

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

Overtemperature Protection

Integrated Signature Resistor

External Hot Swap™ N-Channel MOSFET for Lowest

Power Dissipation and Highest System Efficiency

Programmable Aux Power Support as Low as 9V

Optional Support of Non-Standard Low Voltage PoE

Available in 10-Lead MSOP and 3mm × 3mm DFN

Packages

High Power Wireless Data Systems

Outdoor Security Camera Equipment

Commercial and Public Information Displays

High Temperature Industrial Applications

LT4275 Family

MAX DELIVERED

POWER

LT4275 GRADE

A B C

LTPoE

90W

LTPoE

70W

LTPoE

52.7W

LTPoE

38.7W

25.5W

l l

13W

l l l

LT4275A

VPORT HSGATE

GND

4275 TA01a

IEEEUVLO

HSSRC

AUX

RCLASS

CLS++

PWRGD

T2P

CLS

0.1µF

PORT

DATA

PAIR

SPARE

PAIR

RUN

47nF

3.3k

FDMC86102

OUT

–

ISOLATED

POWER

SUPPLY

OPTO

PSE TYPE

(TO µP)

–

PORT

AUX

(9V TO 60V)

Summary of content (12 pages)

PAGE 1
LT4275 LTPoE++/PoE+/PoE PD Controller Description Features n n n n n n n n n n n n n IEEE 802.3af/at and LTPoE++™ Powered Device (PD) Controller LTPoE++ Supports Power Levels Up to 90W LT4275A 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 LT4275B is IEEE 802.3at/af Compliant LT4275C is IEEE 802.
PAGE 2
LT4275 Absolute Maximum Ratings (Notes 1, 3) VPORT, HSSRC Voltages.......................... –0.3V to 100V HSGATE Current.................................................. ±20mA IEEEUVLO, RCLASS, RCLASS++ Voltages........ –0.3V to 8V (and ≤ VPORT) AUX Current......................................................... ±1.4mA T2P, PWRGD Voltage................................ –0.3V to 100V T2P, PWRGD Current................................................
PAGE 3
LT4275 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 3) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VPORT Operating Input Voltage At VPORT Pin l 23 60 V VSIG VPORT Signature Range At VPORT Pin l 1.5 10 V VCLASS VPORT Classification Range At VPORT Pin l 12.5 21 V VMARK VPORT Mark Range At VPORT Pin, Preceded by VCLASS l 5.
PAGE 4
LT4275 Typical Performance Characteristics VPORT Current vs VPORT Voltage 25k Detection Range 37 T = –40°C T = 25°C T = 75°C T = 125°C 0.3 0.2 35 34 33 32 2 4 6 VPORT VOLTAGE (V) 8 30 –50 10 –25 0 25 50 75 TEMPERATURE (°C) 4275 G01 24.25 5 7 VPORT VOLTAGE (V) Hot Swap OFF –25 0 25 50 75 TEMPERATURE (°C) 2 3 CURRENT (mA) 4 5 4275 G07 –25 0 25 50 75 TEMPERATURE (°C) 125 T2P Frequency 990 DETECT OR MARK TO CLASS CLASS TO MARK 940 11.5 11.0 10.
PAGE 5
LT4275 Pin Functions IEEEUVLO (Pin 1): Hot Swap Turn-on Threshold Level Control. Connect to ground for IEEE compliant turn-on and turn-off (UVLO) voltage thresholds. Leave open for lower turn-on and turn-off voltage thresholds. 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, disables classification and floats the PWRGD pin.
PAGE 6
LT4275 Applications Information Overview VHSON VHSOFF CLASS VPORT 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. Powered device (PD) equipment vendors are running into the 25.5W power limit established by the IEEE 802.3 standard. The LT4275A allows higher power while maintaining backwards compatibility with existing PSE systems.
PAGE 7
LT4275 Applications Information Table 1. Classification Codes, Power Levels and Resistor Selection PD POWER NOMINAL CLASS CLASS AVAILABLE PD TYPE CURRENT 0 13W Type 1 <0.4mA 1 3.84W Type 1 10.5mA 2 6.49W Type 1 18.5mA 3 13W Type 1 28mA 4 25.5W Type 2 40mA 4* 38.7W LTPoE++ 40mA 4* 52.7W LTPoE++ 40mA 4* 70W LTPoE++ 40mA ++ 4* 90W LTPoE 40mA *An LTPoE++ PD will be classified as class 4 by an IEEE 802.3 compliant PSE.
PAGE 8
LT4275 Applications Information 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 less than VAUXT. Use the following equations to set VAUXON and VAUXOFF via R1 and R2 in Figure 4. R1= R2 = R1≥ VAUXON − VAUXOFF VAUXHYS = IAUXH IAUXH + R1  VAUXOFF  − 1  V  AUXT VAUX(MAX) − VAUXT 1.
PAGE 9
LT4275 Typical Applications IEEE 802.3af (Type 1) 13W Powered Device ~ ETHERNET MAGNETICS ~ – ~ + ~ FDN8601 + VPORT CPD 0.1µF SMAJ58A + 3.3k CPORT VIN 47nF VPORT HSGATE – HSSRC ISOLATED POWER SUPPLY PWRGD RUN + VOUT – LT4275A/LT4275B/LT4275C RCLASS RCLASS++ GND IEEEUVLO RCLS T2P AUX 4275 TA02 IEEE 802.3at (Type 2) 25.5W Powered Device ETHERNET MAGNETICS ~ + ~ – ~ + ~ FDN8601 VPORT CPD 0.1µF SMAJ58A + 3.
PAGE 10
LT4275 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DD Package Package 10-Lead Plastic DFNDD (3mm × 3mm) 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699 Rev C) (Reference LTC DWG # 05-08-1699 Rev C) 0.70 ±0.05 3.55 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ±0.10 (4 SIDES) R = 0.125 TYP 6 0.40 ±0.10 10 1.
PAGE 11
LT4275 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MS Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1661 Rev E) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 0.50 0.305 ± 0.038 (.0197) (.0120 ± .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 10 9 8 7 6 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 4.90 ± 0.152 (.193 ± .006) DETAIL “A” 0.497 ± 0.076 (.
PAGE 12
LT4275 Typical Application 25W PD Solution with 12VDC and 24VAC Auxiliary Input VAUX 9V TO 57VDC OR 24VAC B2100 (4plcs) ~ ~ + MMSD4148 (2plcs) 470µF TO ISOLATED POWER SUPPLY MMSD4148 158k 0.1µF FDN8601 13 8.2Ω WÜRTH 7499511001 15 SMAJ58A 16 0.1µF 931k HSGATE 1–12 HSSRC 3.3k 47nF LT4275A/LT4275B 34.