The LM74681 is an ideal diode bridge controller designed to meet input rectifier requirements in PoE PD applications. A very common application is an IEEE 802.3 powered device, which is required to accept voltage in either polarity at its RJ-45 input (polarity agnostics input). Traditional diode bridges have lower efficiency due to the forward drop generated across two conducting diodes. Schottky diode based bridge rectifier offer lower forward drop compared to standard diode bridge however the schottky bridge may not be suitable for high temperature applications. Schottky diode bridges exhibit temperature induced leakage currents. These leakage currents have a voltage dependency that can invalidate the measured detection signature. In addition, these leakage currents can back-feed through the unpowered branch and the unused bridge, violating IEEE 802.3 specifications. Ideal diode bridge circuits are often implemented with discrete components such as a combination of P-channel and N-channel MOSFETs. These bridges usually exhibit poorer performance in terms of quiescent current, transient immunity against supply transients, and wider variation in leakage currents over temperature.

LM74681 offers integrated gate control for the external MOSFET bridge to realize low-loss rectifier solution for PoE PD applications. This device can handle transient voltages up to 100V, which makes it suitable to meet voltage transient requirements in 48V PoE powered applications. LM74681 features a linear ORing gate control mechanism that stops the powered device from allowing current to back-feed into the Ethernet cable. It also incorporates a built-in under-voltage lockout (UVLO) feature to ensure ultra-low quiescent current during both PoE PD detection (VIN < 10.5V) and classification phases (VIN < 20.5V).