Revese voltage protection circuit

This circuit has no ability to deliver useful current as-is. The default mosfet settings in EC are more like what youd find in CMOS logic, not power handling. The AO3400/01 are impressive little devices. They are rated for 5.8A continuous, 33mohm RdsON with 4.5V on the gate and as little as 1V threshold to turn on. They have a max drain to source voltage voltage of only 30V and about 600pF input capacitance so detailed simulations should explicitly include an avalanche diode from source to drain (antiparallel) and external caps between (at least) gate and source. The main thing to do on the fly is play with the channel width and length to get your RdsON close to the rated value when the expected gate voltage is applied, and off without it. Threshold should be no less than 1V.