PoE PD Controller Eliminates Optoisolator

Sep 5, 2007 2:41 PM

Linear Technology’s LTC4268-1 is a PoE interface controller for powered devices (PDs) with NoOpto feedback topology to provide full IEEE 802.3 isolation without the need for optoisolator circuitry. A feedback amplifier senses the output voltage through the transformer winding during the flyback period and uses this voltage to tightly regulate the output. The transformer isolates the load from the input supply and provides feedback, improving output-transient response and overall reliability. The LTC4268-1 provides up to 35 W for 2-pair systems, and as much as 70 W for 4-pair systems.

As the momentum for PoE continues to grow, the LTC4268-1 can enable high-power PoE devices in anticipation of the evolving PoE+ (IEEE 802.3at) standard. The LTC4268-1 offers a programmable switching frequency from 50 kHz to 250 kHz. The controller can also be synchronized to an external oscillator. By incorporating a precision dual-current limit, the LTC4268-1 ensures trouble-free interoperability with any power sourcing equipment (PSE). The device is housed in a 32-pin, 7-mm x 4-mm thermally enhanced DFN package. Pricing begins at $2.40 each in 1000-piece quantities.