The LTC4354 is a negative voltage diode-OR controller that drives two external N-channel MOSFETs. It replaces two Schottky diodes and the associated heatsink, saving power and area. The power dissipation is greatly reduced by using N-channel MOSFETs as the pass transistors. Power sources can easily be ORed together to increase total system power and reliability. When first powered up, the MOSFET body diode conducts the load current until the pass transistor is turned on. The LTC4354 servos the voltage drop across the pass transistors to ensure smooth transfer of current from one transistor to the other without oscillation. The MOSFETs are turned off in less than 1µs whenever the corresponding power source fails or is shorted. Fast turnoff prevents the reverse current from reaching a level that could damage the pass transistors. A fault detection circuit with an open drain output capable of driving an LED or opto-coupler indicates either MOSFET short, MOSFET open or supply failed.
