35W Power over Ethernet PD Controller with Synchronous NoOpto Flyback Controller Bridges the PoE+ Gap

At the heart of the LTC4268-1 is a high-performance switching regulator optimized for isolated PoE applications. The LTC4268-1 incorporates Linear Technology’s patented 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 synchronous flyback converter provides a low part count design with the advantage that additional outputs can be obtained by simply adding windings. Synchronous rectification offers the benefit of higher output power, increased conversion efficiency and improved cross regulation in applications with multiple outputs. The LTC4268-1 offers the flexibility of programmable switching frequency from 50kHz to 250kHz for optimized power supply design. In low-noise system designs, the controller can be synchronized to an external oscillator.

The LTC4268-1 includes a field-proven PD controller front end for worry-free use in hostile PoE environments. By incorporating a precision dual current limit, the LTC4268-1 ensures trouble-free interoperability with any Power Sourcing Equipment (PSE). The LTC4268-1 is capable of handling 750mA with the lowest on-resistance (0.55 Ohm typ) Hot Swap™ MOSFET on the market. The ultra-low FET on-resistance minimizes device heating and improves overall efficiency. For even higher output power, the normal current limit can be disabled, allowing implementation of proprietary, ultra high-power designs.