What this N-channel HEXFET brings to a power stage
The Infineon IRFZ44ZSPBF is a 55 V, 51 A N-channel MOSFET from the HEXFET family, built on planar stripe technology. The D2PAK (TO-263) surface-mount package carries an 80 W power dissipation rating at the case, so the thermal design — PCB copper area and via stitching under the tab — determines how much current it can actually handle in a given layout.
That is the number to use for conduction loss at full load. The maximum gate threshold voltage of 4 V at 250 µA means the device is fully enhanced only when the gate-source voltage exceeds 4 V; a 5 V logic-level gate drive may not saturate it to the minimum Rds(on), so the design should budget for higher on-resistance if the gate drive is below 10 V.
The 80 W power dissipation at the case assumes a proper thermal interface to a heatsink or PCB copper plane — without that, the junction will exceed 175°C well before reaching 80 W in still air.