100 V N-channel in a DirectFET can — conduction loss and thermal path
The IRF7665S2TRPBF is an N-channel power MOSFET rated at 100 V drain-source with a continuous drain current of 4.1 A. The on-resistance is specified at 62 mOhm maximum when driven with 10 V on the gate and 8.9 A drain current — this is the figure to use for conduction-loss budgeting in a synchronous rectifier or primary-side switch.
At 4.1 A continuous, the I²R conduction loss at 62 mOhm is just over 1 W. The total device dissipation is rated at 2.4 W, so the junction-to-ambient thermal path in the DirectFET package must be managed — the copper area on the drain tab and airflow determine the real thermal limit. Gate charge totals 13 nC at 10 V, which keeps the switching losses moderate at frequencies up to a few hundred kHz. The gate threshold is 5 V maximum at 25 µA, so a 10 V gate drive provides ample overdrive for a hard-switched topology.
Junction temperature range and package thermal reality
This matters in a high-ambient enclosure or a motor-drive bay where the MOSFET sits near the heatsink baseplate. The DirectFET package (listed as Bulk in the spec — the part ships in tape-and-reel as the TR suffix indicates) exposes the drain on the top surface for direct heatsinking or PCB copper spreading.
Infineon lists the IRF7665S2TRPBF as Active.