This document describes how to replace ORing diodes with MOSFETs to reduce heat and save space. By using the LTC4354 negative voltage diode-OR controller, near-ideal diode behavior can be achieved, and external N-channel MOSFETs are used to replace the diodes. This design reduces power dissipation, saves board space, and increases the input operating range.
This document describes a design technique for replacing traditional ORing diodes with N-channel MOSFETs actively driven by the LTC4354 controller. This approach eliminates the significant forward voltage drop and power dissipation associated with discrete diodes, which is critical for high availability telecom systems using redundant power supplies or battery feeds.
Using an LTC4354 driving a MOSFET reduces dissipation to 1.8W, whereas a heat sink is required for 6.2W of power dissipation from a Schottky diode.
The device turns off the MOSFET in less than 1us to prevent reverse current from reaching a damaging level.
The open-drain FAULT pin goes high when the voltage drop across a fully on pass transistor exceeds 260mV.