What this ExpressCard switch does on your board
The TPS2231PW is a high-side power switch designed specifically for ExpressCard slots — it routes the 1.5 V and 3.3 V rails from the host to the card through a single 45 mOhm typical Rds(on) path per output. Three outputs each handle up to 1.3 A, with fixed current limiting and over-temperature protection that shuts down the switch before the PCB trace or the card connector suffers damage. Power Good and Status Flag signals give the host controller a clean handshake — the flag asserts when the output is within regulation, so the system knows the card is powered before attempting enumeration.
Rds(on), current rating, and thermal margin
At 45 mOhm typical, the conduction loss at 1.3 A is under 80 mW per channel — low enough that the 20-TSSOP package can dissipate it without airflow in most indoor and industrial enclosures.