LTC4257

1

4257fb

The LTC

interface functions for a device operating in an IEEE

802.3af Power over Ethernet (PoE) system. The LTC4257

simplifies Powered Device (PD) design by incorporating

the 25k signature resistor, the classification current source,

input current limit with thermal foldback, undervoltage

lockout and power good signalling, all in a single 8-pin

package. By incorporating a high voltage power MOSFET

onboard, the LTC4257 provides the system designer with

reduced cost while also saving board space.

The LTC4257 can interface directly with a variety of Linear

Technology DC/DC converter products to provide a cost

effective power solution for IP phones, wireless access

points and other PDs. Linear Technology also provides

solutions for Power Sourcing Equipment (PSE) applica-

tions with quad network power controllers.

The LTC4257 is available in the 8-pin SO and low profile

(3mm

× 3mm) DFN packages.

■

IP Phone Power Management

, LTC and LT are registered trademarks of Linear Technology Corporation.

®

Powered Devices (PDs)

■

Onboard 100V, 400mA Power MOSFET

■

Programmable Classification Current (Class 0-4)

■

Power Good Signal

× 3mm)

DFN Packages

IEEE 802.3af PD

Power over Ethernet

Interface Controller

GND

SMAJ58A

0.1

µF

PWRGD

LTC4257

SHDN

5

µF

MIN

100k

3.3V

TO LOGIC

RTN

SWITCHING

POWER SUPPLY

–48V FROM

POWER SOURCING

EQUIPMENT

(PSE)

4257 TA01

+

–

+

DF01SA

~

~

+

–

Powered Device (PD)

5ms/DIV

50V/DIV

20V/DIV

200mA/DIV

PWRGD

50V/DIV

4225 TA02

LTC4257 Charging 300

µF

Load Capacitor

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

All other trademarks are the property of their respective owners.