2.3 mOhm Rds(on) at 10 V — the conduction loss floor
The AUIRFS8405TRL is an Infineon HEXFET N-channel MOSFET rated for 40 V drain-source breakdown and 120 A continuous drain current. The headline spec is the 2.3 mOhm maximum on-resistance at Vgs=10 V and Id=100 A — that is the conduction loss floor at 25 °C junction temperature. In a 100 A load, the conduction loss sits at 23 W, well within the 163 W power dissipation rating of the D2PAK package when properly heatsunk.
Gate charge and switching loss budget
Total gate charge is 161 nC at Vgs=10 V. That is a substantial charge — the gate driver must source and sink that charge each switching cycle. At 100 kHz switching frequency, the average gate-drive current is 16.1 mA; the driver's peak current capability and the gate-loop inductance determine the turn-on and turn-off times. Plan the gate-drive circuit for at least 2 A peak to keep switching edges clean and avoid Miller-plateau dwell.
Junction temperature range and thermal design
The D2PAK (TO-263) package has an exposed drain tab on the top — the thermal pad on the PCB must be sized to the application's power dissipation. At 163 W maximum dissipation, a multi-layer board with thermal vias under the tab is the baseline; a heatsink on the tab further drops the junction-to-ambient thermal resistance.
Lifecycle and sourcing
No official replacement or second-source alternate is listed; the part is the current production variant in the HEXFET 40 V family.