It is recommended that the external MOSFET (Q1) selection be based on the following criteria:

• The BV_DSS rating should be greater than the maximum system voltage (V_SYS), plus ringing and transients which can occur at V_SYS when the circuit card, or adjacent cards, are inserted or removed.
• The maximum continuous current rating should be based on the current limit threshold (50 mV/R_S), not the maximum load current, since the circuit can operate near the current limit threshold continuously.
• The Pulsed Drain Current spec (I_DM) must be greater than the current threshold for the circuit breaker function (100 mV/R_S).
• The SOA (Safe Operating Area) chart of the device, and the thermal properties, should be used to determine the maximum power dissipation threshold set by the R_PWR resistor. The programmed maximum power dissipation should have a reasonable margin from the maximum power defined by the FET's SOA chart if the LM5067-2 is used since the FET will be repeatedly stressed during fault restart cycles. The FET manufacturer should be consulted for guidelines.
• R_DS(on) should be sufficiently low that the power dissipation at maximum load current (I_L(max)² x R_DS(on)) does not raise its junction temperature above the manufacturer’s recommendation.

If the device chosen for Q1 has a maximum V_GS rating less than 13V, an external zener diode must be added from its gate to source, with the zener voltage less than the maximum V_GS rating. The zener diode’s forward current rating must be at least 110 mA to conduct the GATE pull-down current during startup and in the circuit breaker mode.