News and New Products

Chip enables POE convenience with auxiliary backup

By Maury Wright -- EDN, 1/17/2006

The potential convenience of POE (power over Ethernet) is undeniable. Users can connect devices such as IP (Internet Protocol) phones, remote cameras, or WiFi (wireless-fidelity) access points with no ac adapter. But designers of POE-enabled products (figure) must guard against the possibility that an Ethernet link may not support POE or that users have oversubscribed the power budget of a POE-enabled source. In other words, designers need to prepare for POE power or power from an ac adapter. Targeting this type of power support, the National Semiconductor LM5071 power IC integrates a PD (POE-powered-device) interface and a current-mode dc/dc-converter controller.

An LM5071-based product can operate with ac adapters that output dc voltages from 9.5 to 48V. The dc/dc-converter controller supports various isolated and nonisolated converter topologies, including buck converters. Designers can program functions such as the undervoltage-lockout trip point and hysteresis, as well as adjust the oscillator frequency and duty cycle. Available in lead-free and standard small-footprint TSSOP-16 packages, the IC costs $1.45 (1000).

National Semiconductor, http://www.national.com/pf/LM/LM5071.html.