Linear Technology LTC4257CS8-1, Power-Over-Ethernet Interface Controller, Vsig = 48V, Vout = 3.3V DC671A DC671A Fiche De Données

LTC4257-1

1

42571fb

The LTC

®

4257-1 provides complete signature and power

interface functions for a device operating in an IEEE
802.3af Power over Ethernet (PoE) system. The LTC4257-1
simplifies Powered Device (PD) design by incorporating
the 25k signature resistor, classification current source,
input current limit, undervoltage lockout, thermal over-
load protection, signature disable and power good signal-
ling, all in a single 8-pin package. The LTC4257-1 includes
a precision, dual level current limit circuit. This allows it to
charge large load capacitors and interface with legacy
Power over Ethernet systems while maintaining compat-
ibility with the current IEEE 802.3af specification. By
incorporating a high voltage power MOSFET onboard, the
LTC4257-1 provides the system designer with reduced
cost while also saving board space.

The LTC4257-1 can interface directly with a variety of Lin-
ear 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
network power controllers for Power Sourcing Equipment
(PSE) applications.

The LTC4257-1 is available in the 8-pin SO and low profile
(3mm 

× 3mm) DFN packages.

■

IP Phone Power Management

■

Wireless Access Points

■

Telecom Power Control

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

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■

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Precision Dual Level Current Limit

■

Onboard 25k Signature Resistor with Disable

■

Programmable Classification Current (Class 0-4)

■

Undervoltage Lockout

■

Thermal Overload Protection

■

Power Good Signal

■

Available in 8-Pin SO and Low Profile (3mm 

× 3mm)

DFN Packages

IEEE 802.3af PD

Power over Ethernet Interface

Controller with Dual Current Limit

GND

R

CLASS

R

CLASS

SMAJ58A

0.1

µF

SIGDISA

PWRGD

LTC4257-1

V

IN

SHDN

100k

5

µF

MIN

3.3V

TO LOGIC

RTN

SWITCHING

POWER SUPPLY

V

IN

V

OUT

–48V FROM 

POWER SOURCING

EQUIPMENT

(PSE)

42571 TA01

+

–

+

DF01SA

~

~

+

–

All other trademarks are the property of their respective owners.