9.2.2.7 EMI Filter Consideration

In this example it is assumed that the EMI filter is right after the hot swap and the bulk cap is after the EMI filter. The EMI filter adds significant inductance and needs to be accounted for. During a Hot Short, the inductor builds up significant current that needs to go somewhere after the FET opens. For that a free wheeling diode should be used along with a snubber. For this example a 150 V, SMA diode was used: STPS1150A. The snubber consisted of a 10-Ω resistor in series with a 1-µF ceramic capacitor. In addition a 0.1-µF ceramic cap was tied directly on the output.