270 mOhm Rds(on) — the thermal budget anchor
The BTS308 E3059 is a single-channel high-side power switch from Infineon's PROFET family, built around a vertical N-channel MOSFET with a typical on-resistance of 270 mOhm. That Rds(on) number is the starting point for your conduction loss calculation: at the 1.18 A maximum continuous output, the dissipation is I²R ≈ 0.38 W, which is manageable in the TO-220-5 package but rises fast if you push the load current near the limit in a 150°C ambient. The device switches a load from 4.7 V up to 34 V, covering 12 V and 24 V automotive and industrial rails with margin for load-dump transients.
Fault protection that saves the board
This is a smart switch, not a bare MOSFET — the die integrates current limiting (fixed threshold), open-load detection, overtemperature shutdown, and overvoltage clamping. The auto-restart feature means the output re-enables after a fault condition clears, which is useful for driving lamps or motors where a temporary overload is expected. The input is a simple On/Off logic signal (non-inverting, 1:1 ratio), so no PWM-capable interface — it's a straight enable for the load.
Package and mounting — through-hole for high-reliability connections
The TO-220-5 formed-leads package (P-TO220-5-3 supplier device code) is a through-hole footprint with five pins: load input, load output, ground, and two diagnostic/status pins. The formed leads allow the part to sit flush on the heatsink surface — the metal tab is the drain connection, so the thermal pad area on the PCB or the heatsink interface sets the junction-to-ambient thermal resistance. For the 150°C junction rating, derate the 1.18 A output as the case temperature rises.
For volume BOM positions, this is a stable line with no near-term supply discontinuity.