13 mOhm Rds(on) — the thermal budget anchor
The Infineon BTS443PAUMA1 is a single-channel PROFET high-side switch with a typical on-resistance of 13 mOhm. At 21 A continuous output, the conduction loss is I²R = 5.7 W — that heat has to go somewhere. The PG-TO252-5-11 package's exposed tab is the primary thermal path; a solid copper pour on the PCB landing pad is non-negotiable if you plan to run near the 21 A ceiling.
21 A output — derate before you design
The 21 A maximum output is the fixed current-limit threshold, not a continuous rating at high ambient. The part integrates fixed current limiting, over-temperature, and over-voltage protection — so the switch will fold back before it fries itself. But if your load draws 18 A steady-state in a 85°C enclosure, you'll hit the thermal shutdown long before the current limit. Plan your derating from the junction temperature ceiling of 150°C.
It is still available for existing production runs, but Infineon has flagged it for eventual phase-out.
The load supply range spans 5 V to 36 V, covering 12 V automotive, 24 V industrial, and 5 V logic-level loads. The input is non-inverting and the switch is self-powered from the load supply — no separate Vcc bias rail is required. That simplifies the BOM, but it means the gate drive voltage tracks the load supply, so Rds(on) will be higher at 5 V than at 12 V. At 5 V load, budget for the on-resistance increase versus the 13 mOhm typical at nominal conditions.