DC1145B: 12V @ 0.9A POE, 37 ~ 57V in

Summary

Demonstration circuit 1145B, featuring the LTC®4267, provides a complete IEEE 802.3af Powered Device (PD) interface and isolated 12V at 0.9A power supply solution for use in Power over Ethernet (PoE) applications. An optional connection is included for a 12V auxiliary supply on the secondary side that disables PoE when present.

The LTC4267 integrates the 25k signature resistor, classification current source, thermal overload protection, signature disable and power good signal along with an undervoltage lockout optimized for use with the IEEE required diode bridge. The precision dual level input current limit allows the LTC4267 to charge load capacitors and interface with legacy PoE systems.

The LTC4267 combines the above features with a current mode switching controller designed for driving a 6V rated N-channel MOSFET. It features programmable slope compensation, soft-start, and constant frequency operation, minimizing electrical noise even with light loads.

Specifications

Manufacturer	Analog Devices Inc.
Category	Power Management
Sub-Category	POE - Power Over Ethernet
Eval Board Part Number	505-DC1145B-ND
Eval Board Supplier	Analog Devices Inc.
Eval Board	Normally In Stock
Topology	Current Mode Switching Regulator
Outputs and Type	1 Isolated
Voltage Out	12 V
Current Out	900 mA
Voltage In	37 ~ 57 V
Efficiency @ Conditions	>85%, 57 Vin, 12 V @ 0.5 ~ 0.9 A >85%, 48 Vin, 12 V @ 0.4 ~ 0.9 A >83%, 37 Vin, 12 V @ 0.3 ~ 0.9 A
Features	Current Limit (Adj. or Fixed) Power Good Output Shutdown, Enable, Standby Soft Start Thermal Protection Under Voltage Protection, Brown-Out Voltage Reference
Switching Frequency	200 kHz
Component Count + Extras	52 + 21
Design Author	Linear Technology
Internal Switch	No
Main I.C. Base Part	LTC4267
Application / Target Market	PoE, Power Over Ethernet Security IP Camera VOIP Phones WLAN Access Points
Date Created By Author	2011-06
Date Added To Library	2013-12