Single-cell charger with I²C programmability
The BQ25121AYFPT: It supports constant-current charging up to 300 mA, with the charge current, termination voltage, and safety timer all configurable over the I²C interface — no external resistor dividers or trim pots needed.
The 300 mA max charge current suits batteries in the 200–600 mAh range typical of wireless earbuds, smartwatches, and medical patches — charging a 400 mAh cell at 0.75C rate keeps the charge time under two hours without stressing the cell. The 5.5 V supply maximum means the part runs directly from a USB VBUS (5 V nominal) or a regulated 5 V rail without an external pre-regulator, but it will not survive a 12 V or higher input — a TVS clamp on the input is prudent for hot-plug USB applications.
Housed in a 25-bump DSBGA (0.4 mm pitch, 2.4 mm × 2.4 mm body), the BQ25121AYFPT requires a 2-layer or 4-layer PCB with via-in-pad or microvia fan-out to route the I²C bus, battery, and input power traces — the 0.4 mm pitch is at the limit of standard PCB fabrication without HDI, so confirm your board shop's capability before layout. Available in Tape & Reel (TR) for production pick-and-place or Cut Tape (CT) for prototyping and low-volume builds — the CT option avoids the reel minimum quantity for engineering samples.
RoHS3 compliant (2015/863/EU) with no exemptions — the part ships lead-free and meets EU and UKCA substance restrictions for consumer and medical equipment.