22 mOhm Rds(on) — the conduction-loss ceiling
The TPS2557QDRBRQ1 is a single-channel high-side power switch from TI, AEC-Q100 qualified for automotive electronics. Its 22 mOhm typical Rds(on) means the voltage drop across the switch at 5 A output is roughly 110 mV — low enough that the load sees the full rail voltage even under heavy current, and the package self-heating stays manageable in a 3x3 mm SON.
Adjustable current limit — sizing the protection threshold
The current limit is adjustable via an external resistor. That lets you set the trip point just above the worst-case load current — no headroom padding needed. Combined with over-temperature shutdown and undervoltage lockout, the part protects both the switch and the downstream electronics from a hard short or a dead battery crank.
The 8-VDFN exposed pad draws heat into the PCB copper plane — in a 4-layer board with thermal vias, the effective RthJA stays low enough to sustain 5 A continuous at 105°C ambient.
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