ORing controller for redundant automotive supply rails
The Texas Instruments LM74700QDBVTQ1 is an N+1 ORing controller designed to replace a Schottky diode in redundant power-supply architectures. It drives an external N-channel MOSFET to steer current from the higher-voltage input to the output, blocking reverse current when a supply fails or shorts. Rated for a 3.2V to 65V supply range, it covers 12V and 24V automotive buses as well as 48V telecom rails. The 5A maximum output current is the MOSFET's rating, not the controller's — the actual load is limited by the external FET and its thermal management.
Switching speed and reverse-current blocking
The on-delay of 1.4 µs allows the controller to wait for the input to stabilize before turning on the FET, preventing false triggering during supply transients. The off-delay of 450 ns is the critical number: when the input drops below the output, the controller turns off the FET in under half a microsecond, limiting reverse current to a few hundred milliamps depending on the gate capacitance and load. Because the LM74700QDBVTQ1 has no internal switch, the designer selects the external N-channel FET. The gate drive is sized for standard logic-level and standard-threshold FETs.
The SOT-23-6 package is a compact, 6-pin surface-mount footprint that fits on the back side of a PCB or in tight spaces near the input connector. The 1:1 input-to-output ratio means one controller handles one ORing leg; for N+1 redundancy, each supply rail gets its own LM74700QDBVTQ1 and external FET.