The IRF640NSTRRPBF is marked obsolete by the manufacturer.
The maximum on-resistance is 150 mΩ at a gate drive of 10 V and 11 A drain current. These ratings place it in the medium-voltage, medium-current class suitable for DC-DC converters, power supplies, and motor drives where the bus voltage stays under 200 V and peak currents stay within the 18 A continuous envelope. These switching parameters determine the gate drive requirements and switching losses at frequency — a gate driver capable of sourcing and sinking the charge in the desired switching interval is needed.
D2PAK surface-mount package — design-in considerations
The part comes in a TO-263-3 (D2PAK) surface-mount package with two leads plus a tab.
Gate drive and threshold
The absolute maximum gate-source voltage is ±20 V. For logic-level drive at 5 V, the on-resistance will be higher than the 150 mΩ spec — the 10 V drive condition is the one to design around for full rated performance.