9 mOhm at 30 A — the conduction-loss anchor for a synchronous buck
The BSC889N03LSG: 9 mOhm maximum on-resistance at 30 A drain current with 10 V gate drive. 16 nC total gate charge at 10 V.
Dual current rating — the thermal interface decides the real limit
The datasheet lists 45 A continuous drain current at the case temperature (Tc) and 13 A at ambient (Ta). That spread tells you the silicon can handle 45 A if the exposed pad on the PG-TDSON-8 package is soldered to a large copper plane on a multi-layer board. At 13 A ambient with 2.5 W dissipation (Ta rating), the junction stays below 150 °C only if the board copper does the heatsinking. The 28 W case-power limit assumes a heatsink or chassis contact — without it the thermal impedance through the PCB dominates.
Gate drive window and switching behaviour
At 4.5 V the on-resistance will be higher than the 9 mOhm figure — the 10 V drive is the condition for the minimum Rds(on) spec.
Package and footprint — PG-TDSON-8
It is ROHS3 compliant.