Features

• IEEE802.3af/at and LTPoE++™ 90W Powered Device (PD) with Forward/Flyback Controller
• LT4276A Supports All of the Following Standards:
• LTPoE++ 38.7W, 52.7W, 70W and 90W
• IEEE 802.3at 25.5W Compliant
• IEEE 802.3af up to 13W Compliant
• LT4276B is IEEE 802.3at/af Compliant
• LT4276C is IEEE 802.3af Compliant
• Superior Surge Protection (100V Absolute Maximum)
• Wide Junction Temperature Range (–40°C to 125°C)
• Auxiliary Power Support as Low as 9V
• No Opto-Isolator Required for Flyback Operation
• External Hot Swap™ N-Channel MOSFET for Lowest Power Dissipation and Highest System Efficiency
• >94% End-to-End Efficiency with LT4321 Ideal Bridge
• Available in a 28-Lead 4mm × 5mm QFN Package

Typical Application

Description

The LT®4276 is a pin-for-pin compatible family of IEEE 802.3 and LTPoE++ Powered Device (PD) controllers. It includes an isolated switching regulator controller capable of synchronous operation in both forward and flyback topologies with auxiliary power support.

The LT4276A employs the LTPoE++ classification scheme, receiving 38.7W, 52.7W, 70W or 90W of power at the PD RJ45 connector, and is backwards compatible with IEEE 802.3. The LT4276B is a fully 802.3at compliant, 25.5W Type 2 (PoE+) PD. The LT4276C is a fully 802.3af compliant, 13W Type 1 (PoE) PD.

The LT4276 supports both forward and flyback power supply topologies, configurable for a wide range of PoE applications. The flyback topology supports No-Opto feedback. Auxiliary input voltage can be accurately sensed with just a resistor divider connected to the AUX pin.

The LT4276 utilizes an external, low R_DS(ON) N-channel MOSFET for the Hot Swap function, maximizing power delivery and efficiency, reducing heat dissipation, and easing the thermal design.