Single-cell Li-ion fuel gauge with Impedance Track™ learning
The BQ27621YZFR-G1A is a battery fuel gauge from Texas Instruments' Impedance Track™ series, designed for single-cell Lithium Ion packs. It communicates over an I²C interface, reporting state-of-charge based on a patented algorithm that learns the battery's impedance over time — meaning the accuracy improves after the first few charge-discharge cycles, unlike a simple voltage-table gauge that drifts as the cell ages. If your system sees sustained temperatures above 85°C at the battery pack, this part won't work — the gauge itself is the limit, not the cell.
Housed in a 9-ball DSBGA (9-UFBGA) package, the BQ27621YZFR-G1A has a 0.5 mm ball pitch. That's a fine-pitch BGA — the PCB needs a solder-mask-defined pad with a via-in-pad or microvia fan-out under the balls. Hand soldering is impractical; rework requires a hot-air station with a nozzle small enough to avoid disturbing neighbouring components.
The part is ROHS3 compliant. No special handling for lead-free solder — standard SAC305 reflow profile works.