9 mOhm Rds(on) at 15 A — conduction loss anchor for the SMPS stage
The IRF3709SPBF is an N-channel HEXFET power MOSFET from Infineon (formerly International Rectifier), rated 30 V drain-source with a continuous drain current of 90 A. The 3 V maximum gate threshold at 250 µA confirms it is fully enhanced by a standard 5 V gate drive rail. Total gate charge is 41 nC at 5 V, which sets the switching energy per cycle and the gate driver peak current requirement. At a 200 kHz switching frequency, the average gate drive current is roughly 8.2 mA — well within a typical 1 A to 2 A driver's capability, though the peak current during the Miller plateau still needs to be budgeted.
Junction rating to 150 °C — thermal headroom for enclosed supplies
For a 3.1 W device, the junction-to-ambient thermal resistance must be kept below 40 °C/W to stay within the 150 °C ceiling at full dissipation in a 25 °C ambient — this typically requires a copper pour on the drain tab footprint or a small heatsink. The 0.0027 µF (2.7 nF) output capacitance is the energy stored on the die output — it contributes to switching losses during hard-switching transitions and should be factored into the FET's Coss-related loss term in the converter design.
The buyer can commit the BOM position for current production runs without obsolescence risk.