During input supply failure or micro-short conditions, huge reverse current can flow into the input, discharging the load capacitors used for holdup. Ideal diode controllers feature a very fast reverse comparator and strong gate drive to pull down the gate to source voltage to turn OFF the MOSFET. The internal reverse comparator monitors the voltage across anode and cathode and if it exceeds the reverse current threshold, external MOSFETs gate is shorted to anode (source) with strong pulldown current. Reverse comparator delay and gate pulldown current determine how fast the MOSFET can be turned off. Total reverse current turn off delay includes reverse comparator delay and MOSFET turn off delay.

TI's ideal diode controller LM74700-Q1 features a very low reverse comparator delay of 0.75 µs maximum and gate pulldown current of 2.37A. A MOSFET with 5 nF of gate capacitance can be turned off within 0.75 µs + 21 ns = 0.77 µs, with 21 ns required to discharge 5 nF gate capacitance by 2.37 A of gate pulldown current. Figure 6-5 shows LM74700-Q1 reacting quickly within 0.77 µs to a short circuit at battery input. This prevents hold capacitors at the output from discharged into the shorted battery input line.

Figure 6-5 Input Short Circuit Response of LM74700-Q1