100 V N-channel in a DirectFET can — the thermal path is the story
The IRF6645TRPBF is an Infineon HEXFET N-channel MOSFET rated for 100 V drain-source with a maximum Rds(on) of 35 mOhm at 5.7 A drain current and 10 V gate drive. The DirectFET Isometric SJ package is a metal-can SMT package with a solderable top-side drain contact — the drain tab is the top of the can, not a bottom pad. This changes the thermal path: heat conducts up through the can into a heatsink or board copper, rather than down through a traditional exposed pad. The PCB layout needs a thermal land on the top layer under the can, and the reflow profile must accommodate the can's mass.
Rds(on) and current rating — the package derating trap
The continuous drain current is rated at 5.7 A at 25 °C ambient (Ta) but 25 A at 25 °C case temperature (Tc). That 4.4× spread tells you the die can carry 25 A if the case is held at 25 °C — but in still air at room temperature, the package self-heating limits you to 5.7 A. The 2.2 W maximum power dissipation at Ta versus 42 W at Tc confirms that the board copper area and any airflow or heatsink directly determine the usable current.