Linear Tech Adds 35W PoE PD Controller with Synchronous NoOpto Flyback Controller
Linear Technology introduced the LTC4268-1, a Power over Ethernet (PoE) interface controller with a synchronous, current mode, switching regulator for delivering precise regulation and high efficiency to power-hungry Powered Devices (PDs). The LTC4268-1 provides up to 35W for 2-pair systems and as much as 70W for 4-pair systems. As the momentum for PoE continues to grow, the LTC4268-1 bridges the gap to enable development of innovative high-power PoE devices in anticipation of the evolving PoE+ (IEEE 802.3at) standard.
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 50 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 what is claimed to be the lowest on-resistance (0.55Ω typ) Hot Swap™ MOSFET on the market. The ultra-low FET on-resistance is said to minimize device heating and improve overall efficiency. For even higher output power, the normal current limit can be disabled, allowing implementation of proprietary, ultra high-power designs.
Specified over the commercial and industrial temperature ranges, the LTC4268-1 is offered in a space saving 32-pin 7mm x 4mm thermally enhanced DFN package. Available immediately, pricing begins at $2.40 each in 1,000 piece quantities.
