Features

• 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 802.3at 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

Typical Application

Description

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.