LT4321

1

4321f

For more information www.linear.com/LT4321

Typical applicaTion

FeaTures

DescripTion

PoE Ideal Diode Bridge

Controller

The LT®4321 is a dual ideal diode bridge controller that

enables a Power over Ethernet (PoE) powered device

(PD) to receive power in either voltage polarity from

RJ-45 data pairs, spare pairs, or both. The LT4321 and

eight N-channel MOSFETs replace the eight diodes in a

passive PoE rectifier bridge. The LT4321 eases thermal

design and increases delivered power.

An internal charge pump allows an all-NMOS bridge

eliminating larger and more costly PMOS switches. The

LT4321 works with 2-pair and 4-pair applications. High

impedance input sense pins prevent reverse current on

unused pairs. If the power source fails or is shorted, a

fast turn-off minimizes reverse current transients. Unlike

discrete ideal bridge solutions, the LT4321 will operate

through transients without enabling the MOSFETs on

unpowered pairs.

Powered Device for PoE (to 13W), PoE+ (to 25.5W), or Linear LTPoE++ (to 90W) Systems

applicaTions

L

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

PowerPath and LTPoE++ are trademarks of Linear Technology Corporation. All other trademarks

are the property of their respective owners.

n

Reduces Heat, Eliminates Thermal Design Problems

n

Maximizes Power Efficiency

n

Less than 800µA Quiescent Operating Current

n

Fully Compatible with IEEE 802.3 Detection and

Classification

n

IEEE 802.3 Compliant When Paired with a Powered

Device (PD) Controller

n

Works with 2-Pair and 4-Pair PoE Applications

n

Compatible with PoE, PoE+, and LTPoE++™

n

100V Absolute Maximum Voltage

n

H-Grade Version Operates Up to 125°C

n

16-Lead 4mm × 4mm QFN Package

n

PoE/PoE+/ LTPoE++ Powered Devices

n

DC Polarity Correction and Ideal Diode-ORing of

Telecom Supplies

4321 TA01

LT4321

TG36

BG12

BG36

IN36

IN45

IN78

IN12

DATA

PAIRS

1

2

3

6

4

5

8

7

SPARE

PAIRS

OUTN

EN

OUTP

VPORT

PWRGD

HSGATE

LT4275

GND

EN

TG12

BG78

TG45

TG78

BG45

HSSRC

10µF

ISOLATED

POWER

SUPPLY

GND

RUN

0.1µF

SMAJ60A

–

+

+