Linear Technology diode bridge controller maximizes power efficiency in PoE driven devices
The LT4321 dual diode bridge controller replaces two diode bridge rectifiers with low-loss N-channel MOSFET bridges to increase the available power and heat dissipation in a Power over Ethernet (PoE) Powered Device (PD). The diode bridge controller meets IEEE 802.3 PoE specifications required for PDs to accept DC supply voltages of any polarity over their Ethernet inputs.
Linear Technologies has developed a dual ideal diode bridge controller that enables a Power over Ethernet (PoE) powered device (PD) to receive power in either voltage polarity from RJ-45 data pairs, spare pairs, or both. The LT4321 dual diode bridge controller and eight N-channel MOSFETs replace the eight diodes in a passive PoE rectifier bridge to ease the thermal design and increase delivered power.
The space and power-efficient LT4321 dual active bridge rectifies and smoothly combines power from both the data and spare pairs into a single, polarity correct supply output. Circuit size and cost are reduced as the enhanced power efficiency eliminates heat sink requirements. Power savings of 10x or more enables PDs to stay within PoE classification levels or to add functionality while maintaining class.
Carefully designed to be compliant with IEEE 802.3, the LT4321’s bias current does not corrupt detection and classification. Working with 2- or 4-pair Ethernet, the controller is compatible with PoE, PoE+ and LTPoE++™ standards. An integrated charge pump provides the gate drive for the eight low on-resistance N-channel MOSFETs without requiring external capacitors. Although designed for PoE PDs, the LT4321 dual diode bridge controller provides an operating range from 20V to 80V with a 100V absolute maximum, making it suitable for telecom applications employing batteries or reversible supplies. The dual-polarity enable pins provide shutdown capability to the LT4321, reducing its bias current to 32µA from the 0.5mA operating current.
Specified over the -40°C to 125°C ambient temperature range, the LT4321 dual diode bridge controller is offered in a compact 16-pin 4mm x 4mm QFN package. Pricing begins at $2.95 each for 1,000-piece quantities.
For more information, go to the LT4321 dual diode bridge controller product page
Author: Garth Miller Published: 05 May 2014