P-channel 60 V MOSFET in TO-252 — the high-side switch you can count on
The NP36P06SLG-E1-AY: The NP36P06SLG--AY is a P-channel power MOSFET from Renesas, rated for 60 V drain-to-source and 36 A continuous drain current at the case temperature.
The 30 mOhm Rds(on) at Vgs=10 V is the figure you use for worst-case conduction loss at 18 A load current. At lower gate drive (4.5 V minimum) the on-resistance rises. Gate charge is 52 nC at 10 V. The 3200 pF input capacitance at 10 V drain-source confirms the gate drive needs a clean, low-inductance path.
Thermal reality — 1.2 W at ambient, 56 W at case
The 1.2 W dissipation limit at 25 °C ambient is the board-level constraint in still air — that is about 3.5 A continuous in a typical layout. The 56 W at the case assumes the TO-252 tab is soldered to a large copper plane or heatsink.