LTC4257CS8-1 Power Switch ICs POE IEEE 802.3af PD Power over Ethernet Interface Controller

Description

The LTC4257-1 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 asingle 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 ofLin-
ear' Technology DC/DC converter products to provide acost
effective power solution for IP phones, wireless access
points and other PDs. Linear Technology also provides
network power contrllrs for Power Sourcing Equipment
(PSE) applications.
The LTC4257-1 is available in the 8-pin S0 and low profile
(3mm x 3mm) DFN packages.

FEATURES

■Complete Power Interface Port for IEEE 802@ .3af
Powered Devices (PDs)
■Onboard 100V, 400mA Power MOSFET
■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 x 3mm)
  DFN Packages

APPLICATIONS
■IP Phone Power Management
■Wireless Access Points
■Telecom Power Control

1. PoE Interface Controller: The LTC4257CS8-1 serves as an interface controller for Powered Devices (PDs)

in PoE applications, allowing them to receive power and data over Ethernet cables.

1. IEEE 802.3af Compliance: The IC complies with the IEEE 802.3af standard, which defines the specifications

for delivering power over Ethernet cables.

1. Power Switching: The LTC4257CS8-1 integrates power switching circuitry, allowing it to control the power

delivery to the connected PD.

1. PD Detection and Classification: The IC includes detection and classification features to identify the power

capabilities of the Power Sourcing Equipment (PSE) and negotiate the appropriate power level for the PD.

1. Overcurrent Protection: The LTC4257CS8-1 incorporates overcurrent protection mechanisms to prevent

excessive current draw and protect the PD from damage.

1. Integrated DC-DC Converter: The IC includes an integrated DC-DC converter, enabling efficient power

conversion for the PD.

1. Package: The LTC4257CS8-1 is available in an 8-lead SOIC (Small Outline Integrated Circuit) package.