60 V, 280 mA small-signal switch in a SOT323 footprint
The BSS138WH6433XTMA1: That combination — a 60 V blocking voltage paired with a sub-300 mA current rating — puts it squarely in the small-signal switching role: level translation, load switches under 200 mA, relay and solenoid drivers, and logic-level interfacing where a BJT's base drive overhead is unwanted.
On-resistance and drive voltage — the conduction loss picture
That is a typical small-signal figure — at 200 mA the conduction loss is I²R = 0.04 × 3.5 = 140 mW, which is within the 500 mW package dissipation limit but leaves little margin at elevated ambient.
Temperature grade and package — where this part fits on the board
The junction temperature range spans -55°C to 150°C, the full industrial and automotive temperature band. That qualifies it for under-hood electronics, outdoor telecom, and any environment where the PCB sees thermal cycling from cold soak to hot shutdown. The package is SC-70 / SOT-323 (supplier code PG-SOT323), a three-lead surface-mount outline with a 1.3 mm × 2.0 mm footprint — small enough to fit in a dense mixed-signal layout alongside passives and logic, but large enough for hand-solder rework in prototyping.