What this fuel gauge does in a 1S Li-ion pack
The BQ27741YZFT-G1 is a multi-function controller that monitors a single lithium-ion cell — it tracks charge, discharge, and reports remaining capacity over an I²C or HDQ bus. On-chip fault protection covers over-current, over-temperature, over/under-voltage, and short-circuit conditions, which means the gauge doubles as a safety monitor and you can skip a separate protector IC in many portable builds.
Package and interface — what the BOM needs to know
The I²C bus runs at standard and fast mode; HDQ is a single-wire TI protocol. Either interface works for a host MCU that already has an I²C peripheral, saving a GPIO. CT works for prototype or low-volume builds.