Power Electronics

Chip Enables PoE Devices to Run off AC Adapters

National Semiconductor’s LM5071 is designed for Power-over-Ethernet (PoE) devices that operate from alternative power sources or the PoE-enabled network. The single-chip solution is a Powered Device (PD) interface and dc-dc converter IC that simplifies the design of a variety of PoE applications requiring an auxiliary power source, such as an ac adapter.

Devices powered by a PoE network include IP phones and security cameras. Operating these PoE devices from alternate power sources often is necessary to relieve the burden on the Power Sourcing Equipment (PSE) or to operate the device on a network that is not PoE-enabled. Current solutions limit the choice of auxiliary power sources, which can drive up overall system cost or complexity.

The device is an IEEE 802.3af-compliant PD interface port and pulse-width modulation (PWM) controller designed to accept power from external ac adapters. The device integrates a PD front end that accepts power from the PSE or auxiliary power to a single chip with a dc-dc controller that steps down the input voltage to power various PD loads.

The LM5071 is fabricated with National’s ABCD150-XV1 high-voltage analog bipolar/CMOS/DMOS technology and offers advantages such as an integrated, high-frequency, current-mode dc-dc controller, user-programmable undervoltage threshold and hysteresis, and a highly accurate fault current control loop. It features a maximum input voltage of 80 V, user-programmable oscillator frequency up to 1 MHz and overtemperature protection, as well as a voltage reference and high-performance error amplifier for nonisolated applications.

National’s LM5071 is available in lead-free and standard small-footprint TSSOP-16 packages. The product is priced at $1.45 each in 1000-unit quantities.

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