Usually bulk capacitors are placed on the output due to various reasons such as uninterrupted operation during power interruption or micro-short at the input, hold-up requirements for doing a memory dump before turning of the module and filtering requirements as well. This design considers minimum bulk capacitors requirements for meeting functional status "A" during LV124 E10 test case 2 100-µs input interruption. To achieve functional pass status A, acceptable voltage droop in the output of LM7480x-Q1 is based on the UVLO settings of downstream DC-DC converters. For this design, 2.5-V drop in output voltage for 100 µs is considered and the minimum hold-up capacitance required is calculated by

Equation 3.

Minimum hold-up capacitance required for 2.5-V drop in 100 µs is 200 µF. Note that the typical application circuit shows the hold-up capacitor as optional because not all designs require hold-up capacitance.