IEEE 802.3af PD Power over Ethernet Interface Controller with Dual Current Limit

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 overload protection, signature disable and power good signalling, 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 compatibility 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 ADI DC/DC converter products to provide a cost effective power solution for IP phones, wireless access points and other PDs. Analog Devices 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 x 3mm) DFN packages.

Applications

* IP Phone Power Management

* Wireless Access Points

* Telecom Power Control

* 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