5 mOhm at 20 A — the conduction-loss ceiling
The IAUZ40N06S5L050ATMA1: For a 20 A load, the dissipation at 5 mOhm is 2 W; at 100 °C junction the Rds(on) roughly doubles per the datasheet's normalized curve, so budget 4 W in a hot environment.
AEC-Q101 and the 175 °C junction ceiling
AEC-Q101 qualified — this part is released for automotive stress grades: under-hood, transmission control, and chassis-domain power stages. The junction temperature range extends to 175 °C, 25 °C above the typical 150 °C limit, which buys margin in engine-bay or exhaust-adjacent mounting where ambient air hits 125 °C. The PG-TSDSON-8-33 package has an exposed drain pad; the PCB copper area under that pad sets the RthJA, so the layout determines whether the 71 W power dissipation rating is reachable or thermally limited.
Gate charge and drive budget
Total gate charge is 36.7 nC at 10 V. The input capacitance Ciss is 2500 pF at 30 V Vds; this sets the switching loss during the Miller plateau.