Single-cell USB charger in a 2x3 mm WSON
The Texas Instruments BQ24055DSST is a linear single-cell Li-Ion/Polymer charger IC designed for USB-powered portable devices. It charges a 4.2 V battery pack at a programmable constant current up to 800 mA, with the input supply rated to 28 V maximum. The 12-WSON (2x3 mm) package with exposed pad provides a thermal path through the pad to the PCB copper.
Charge current and protection — what sets the BOM
The 800 mA maximum charge current is set with a single programming resistor, giving the BOM engineer control over the charge rate without a separate current-sense resistor. The constant-current phase is programmable; the termination voltage is fixed at 4.2 V for standard single-cell Li-Ion and Li-Polymer packs. On-chip fault protection covers over-temperature, over-voltage, and short-circuit conditions — these reduce the external component count compared to a charger that requires a separate supervisor IC or thermistor network.