4 mOhm Rds(on) at 95 A — the conduction-loss anchor
The AUIRL1404S is an N-channel HEXFET power MOSFET from Infineon Technologies, rated for 160 A pulsed drain current at a 40 V drain-source breakdown voltage. The 4 mOhm value is specified at 95 A, not the 160 A peak — the buyer's steady-state current should be sized against the Rds(on) at the operating current and junction temperature, not the pulsed maximum. At 175 °C junction, the on-resistance roughly doubles from the 25 °C figure, so a 50 A continuous load sees about 8 mOhm hot and dissipates 20 W — well within the 3.8 W package limit only if the PCB copper and airflow handle the thermal resistance.
175 °C junction — the full automotive temperature envelope
Rated for -55 to 175 °C junction temperature, the AUIRL1404S covers the engine-bay temperature band that AEC-Q101-qualified parts serve. A 105 °C ambient under-hood environment leaves 70 °C of junction-to-ambient margin for self-heating — enough for a 20-30 A continuous load with a moderate heatsink or a large copper pour on the PCB. But the peak current during the Miller plateau determines the switching time — a driver with 2 A peak capability turns the FET on in roughly 70 ns, keeping switching losses low.