The important MOSFET electrical parameters are the maximum continuous drain current I_D, the maximum drain-to-source voltage V_DS(MAX), the maximum gate-to-source voltage V_GS(MAX) and the drain-to-source On resistance R_DSON.

The maximum continuous drain current, I_D, rating must exceed the maximum continuous load current. The maximum drain-to-source voltage, V_DS(MAX), must be high enough to withstand the highest differential voltage seen in the application. This requirement would include any anticipated fault conditions. The maximum V_GS LM74502 can drive is 13.9 V, so a MOSFET with 15-V minimum V_GS rating must be selected. If a MOSFET with V_GS rating < 15 V is selected, a zener diode can be used between GATE to SRC pin to clamp V_GS to safe level.

To reduce the MOSFET conduction losses, lowest possible R_DS(ON) is preferred. Selecting a MOSFET with RDS(ON) that gives VDS drop 20 mV to 50 mV provides good trade off in terms of power dissipation and cost.

Thermal resistance of the MOSFET must be considered against the expected maximum power dissipation in the MOSFET to ensure that the junction temperature (T_J) is well controlled.