A gate discharge timer decides the time duration for which external MOSFET is kept on after the LM74501-Q1 fall below its PoR threshold (V_PORF) or when EN pin is pulled low. A ISO7637-2 pulse 1 transient lasts for typically 2 ms. At the end of 2-ms ISO7637-2 pulse 1, amplitude has already fallen to 10% of its peak value. Assuming a ISO7637-2 pulse 1 transient with amplitude of –150 V, at the end of 2 ms, the voltage seen by the LM74501-Q1 is around –15 V. With a VDS rating of external MOSFET of 40 V, the gate discharge timer capacitor, C_T, can be selected such that external FET remains on for less than 2 ms. A C_T timer capacitor value of 22 nF is selected for the given MOSFET as per Equation 2.