Built-in resistors shrink the BOM
The BCR166W integrates a 4.7 kOhm resistor in the base leg and a 47 kOhm resistor from emitter to base, so the transistor turns on and off with a single GPIO line — no external biasing network needed. That saves two passives per channel and cuts placement cost on high-count boards.
Saturation voltage keeps losses low
Vce(sat) maxes at 300 mV with 500 µA base drive and 10 mA collector current. For a 5 V logic rail switching a relay coil or LED string, that conduction drop is low enough to skip a heatsink in most ambient conditions.
Package and footprint fit
Board area is minimal — roughly 2.0 x 2.1 mm — so it fits dense layouts in portable or space-constrained designs.
Listed as active on the Infineon product status.