Features

• Reduces Heat, Eliminates Thermal Design Problems
• Maximizes Power Efficiency
• Less than 800μA Quiescent Operating Current
• Fully Compatible with IEEE 802.3 Detection and Classification
• IEEE 802.3 Compliant When Paired with a Powered Device (PD) Controller
• Works with 2-Pair and 4-Pair PoE Applications
• Compatible with PoE, PoE+, and LTPoE++™
• 100V Absolute Maximum Voltage
• H-Grade Version Operates Up to 125°C
• 16-Lead 4mm × 4mm QFN Package

Typical Application

Description

The LT®4321 is a dual ideal diode bridge controller that enables a Power over Ethernet (PoE) powered device (PD) to receive power in either voltage polarity from RJ-45 data pairs, spare pairs, or both. The LT4321 and eight N-channel MOSFETs replace the eight diodes in a passive PoE rectifier bridge. The LT4321 eases thermal design and increases delivered power.

An internal charge pump allows an all-NMOS bridge eliminating larger and more costly PMOS switches. The LT4321 works with 2-pair and 4-pair applications. High impedance input sense pins prevent reverse current on unused pairs. If the power source fails or is shorted, a fast turn-off minimizes reverse current transients. Unlike discrete ideal bridge solutions, the LT4321 will operate through transients without enabling the MOSFETs on unpowered pairs.