The MOSFET is the most critical part of the hot swap control circuit. This is the main switch which, if damaged, could result in the board not powering up or never powering down. Selection begins by determining the maximum operating current, multiplying this by 2, and looking for current ratings higher than the result. This elevated rating will protect against surges and transients that may damage the MOSFET. In high current systems, the RDSon is very important in that the lower the better since high “on” resistances will result in voltage drops and power loss. To determine the maximum voltage required, use the same approach as when determining the current in that the rated Vds of the MOSFET should be greater than 2x the nominal voltage to protect against transients.