55 V, 49 A, 17.5 mOhm — the switching sweet spot
The IRFZ44NSPBF is an N-channel enhancement-mode MOSFET from Infineon's HEXFET series, built on planar stripe technology. The D2PAK (TO-263) surface-mount package suits automated assembly on power-ground planes with a thermal pad for heatsinking.
Gate charge and switching losses
With a maximum gate charge of 63 nC at 10 V drive, this part falls in the moderate-charge class for a 49 A FET. For a 100 kHz switching frequency, the gate-drive power loss is roughly Qg × Vgs × fsw = 63 nC × 10 V × 100 kHz = 63 mW, which is manageable with a standard gate-driver IC. The input capacitance of 1470 pF at 25 V drain-source gives a rough idea of the switching speed — expect turn-on and turn-off delays in the tens of nanoseconds with a 10 Ω gate resistor.
Temperature range and thermal management
The maximum power dissipation is 3.8 W at 25°C ambient (still air) and 94 W at 25°C case temperature. The 94 W figure assumes the case is held at 25°C via a heatsink; in practice, a TO-263 on a 1 oz copper pad on a 2-layer board will dissipate roughly 2–3 W before the junction hits 175°C in free air. For continuous 49 A, a substantial heatsink or forced airflow is mandatory — the junction-to-case thermal resistance is not listed here, but the 94 W rating at Tc = 25°C implies roughly 1.6°C/W junction-to-case.
Supplied in a D2PAK (TO-263-3, 2 leads plus tab) surface-mount package. The gate threshold voltage is 4 V maximum at 250 µA drain current, so logic-level drive at 3.3 V will not fully enhance the channel — a 5 V or 10 V gate drive is required for rated Rds(on).
This means no last-time-buy risk for new designs, and the usual supply-channel availability through independent distribution. The part is RoHS-compliant as indicated by the 'SPBF' suffix (lead-free plating).