P-channel load switching — why this part fits
The IRF9540NLPBF is a P-channel HEXFET MOSFET from Infineon in a TO-262 through-hole package. P-channel polarity means you can switch the high side of a power rail without a charge pump — the gate is pulled low to turn it on, which simplifies the drive circuit in battery-protection, reverse-polarity protection, and load-switch applications. The 100 V Vdss rating handles 48 V telecom rails, 72 V industrial buses, and 12 V/24 V automotive systems with margin.
At lower gate voltages the Rds(on) climbs — the datasheet curve shows roughly double at 5 V, so this part is optimised for 10 V gate drive, not logic-level signals. If your microcontroller drives the gate directly through a level shifter, budget the gate charge: 110 nC at 10 V means a 1 A gate driver can switch it in about 110 ns; a weaker driver stretches the switching edge and increases crossover loss.
Maximum power dissipation is 3.1 W at ambient (Ta) and 110 W at the case (Tc) — the case rating assumes a good heatsink or metal-chassis mount through the TO-262 tab. The 150°C Tj max means you can push the part hard in a pulsed load, but continuous dissipation needs the heatsink sized to keep the junction below that ceiling.
It is a current-production Infineon part in the long-running HEXFET family, so supply is stable through standard distribution. For BOM planning, the base product number IRF9540 covers multiple package variants (TO-220, D²Pak, TO-262); the NLPBF suffix specifies the TO-262 lead-formed version with lead-free plating.