IEEE 802.3at PD with Synchronous No-Opto Flyback Controller and 12V Aux Support

The LTC4278 is an integrated Powered Device (PD) controller and switching regulator intended for high power IEEE 802.3at and 802.3af applications. With a wide input voltage range, the LTC4278 is specifically designed to support PD applications that include a low-voltage auxiliary power input such as a 12V wall adaptor. The inclusion of a shutdown pin provides simple implementation of both PoE and auxiliary dominate applications. In addition, the LTC4278 supports both 1-event and 2-event classifications as defined by the IEEE, thereby allowing the use in a wide range of product configurations.

The LTC4278 synchronous, current mode, flyback controller generates multiple supply rails in a single conversion step providing for the highest system efficiency while maintaining tight regulation across all outputs. The LTC4278 includes Linear Technology’s patented No-Opto feedback topology to provide full IEEE 802.3 isolation without the need of an opto-isolator circuit. A true soft-start function allows graceful ramp-up of all output voltages.

The LTC4278 is available in a space saving 32-pin DFN package.

Applications

* VoIP Phones with Advanced Display Options

* Dual-Radio Wireless Access Points

* PTZ Security Cameras

* RFID Readers

* Industrial Controls

* 25.5W IEEE 802.3at Compliant (Type 2) PD

* 10V to 57V Auxiliary Power Input

* Shutdown Pin for Flexible Auxiliary Power Support

* Integrated State-of-the-Art No-Opto Synchronous Flyback Controller

* – Isolated Power Supply Efficiency >92%

* – 88% Efficiency Including Diode Bridge and Hot Swap™ FET

* Superior EMI Performance

* Robust 100V 0.7Ω (Typ) Integrated Hot Swap MOSFET

* IEEE 802.3 at High Power Available Indicator

* Integrated Signature Resistor and Programmable Class Current

* Undervoltage, Overvoltage and Thermal Protection

* Short-Circuit Protection with Auto-Restart

* Programmable Soft-Start and Switching Frequency

* Complementary Power Good Indicators

* Thermally Enhanced 7mm × 4mm DFN Package