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. For a 100 kHz switching frequency, the average gate-drive current is Qg × f = 3.67 mA — well within a standard gate-driver IC's output capability. The input capacitance Ciss is 2500 pF at 30 V Vds; this sets the switching loss during the Miller plateau.