The Infineon BTS409L1 E3062A is a single-channel PROFET high-side power switch — it connects a 5 V to 34 V load to the supply rail under logic control, with integrated protection that saves board space. The 160 mOhm typical Rds(on) sets the conduction loss floor: at 1.8 A the dissipation is about 0.5 W, which the PG-TO263-5-2 package's exposed tab sinks to the board copper.
The 160 mOhm typical on-resistance is the value at 25°C junction; expect it to roughly double at 150°C junction. If the load draws 1.8 A continuously, the I²R loss at temperature could reach 1 W — that copper area on the PG-TO263-5-2 tab needs to be generous. The part includes over-temperature shutdown, so a marginal heatsink causes cycling rather than immediate failure, but the thermal pad layout should still follow the datasheet's recommended footprint.