55 V, 49 A, 17.5 mΩ — what these ratings mean for your power stage
The IRFZ44NLPBF is an N-channel enhancement-mode power MOSFET from Infineon's HEXFET series, built with planar stripe technology.
Gate drive and switching: the 10 V requirement and 63 nC gate charge
The drive voltage for achieving the rated Rds(on) is 10 V — this is not a logic-level MOSFET. At 5 V gate drive the on-resistance roughly doubles, so the design must provide a 10 V gate-source rail or a dedicated gate driver capable of sourcing and sinking the 63 nC gate charge (Qg at 10 V).
Thermal management: 94 W case-limited, 3.8 W ambient
Maximum power dissipation is 94 W when the case is held at 25 °C (Tc), versus only 3.8 W in free air at 25 °C ambient (Ta). That gap tells you this part absolutely requires a heatsink or a thermal path to a metal chassis for any load above a few watts. The TO-262 (I²Pak) through-hole package with a metal tab is designed for bolting to a heatsink or PCB copper plane.
For new designs, select a current-production alternative (such as the IRFZ44NPBF, still active at time of writing, or a newer HEXFET like the IRLZ44NPBF if logic-level drive is acceptable).