3.1 mOhm at 75 A — the conduction loss floor
The IRL1404ZPBF is an Infineon HEXFET N-channel MOSFET rated 40 V drain-source and 75 A continuous drain at 25 °C case temperature. The headline spec is the 3.1 mOhm maximum on-resistance at Vgs=10 V and Id=75 A — at full load the I²R loss is under 18 W, which keeps the junction within the 175 °C ceiling with a moderate heatsink. The logic-level gate threshold of 2.7 V max at 250 µA means a 5 V or 3.3 V MCU output can turn it on hard, though the datasheet recommends 4.5 V drive for the lowest Rds(on).
175 °C junction — where this 40 V FET goes
The operating junction range spans -55 to 175 °C, which is wider than the typical 150 °C ceiling for logic-level FETs. That 25 °C headroom matters in under-hood automotive, industrial motor-drive enclosures, and downhole instrumentation where ambient air hits 125 °C and the junction needs room to breathe under ripple current. The TO-220AB package with the metal tab solders to a PCB copper plane or bolts to a chassis heatsink — the 230 W power dissipation rating assumes the tab is held at 25 °C.
110 nC gate charge — sizing the driver
Total gate charge at 5 V is 110 nC. For a 100 kHz switching regulator, that translates to 11 mA of average gate-drive current — well within a standard half-bridge driver IC. The input capacitance of 5080 pF at 25 V drain-source sets the Miller plateau width; a gate resistor in the 10–22 Ω range keeps the switching edge under control without excessive ringing. Through-hole mounting in the TO-220-3 footprint means the gate-drive loop can be kept tight with a local resistor and Schottky catch diode soldered directly to the leads.