Linear charger for small Li-Ion packs
The Texas Instruments BQ25121YFPR is a single-cell linear Li-Ion charger delivering up to 300 mA charge current, with the charge current set via an I²C interface for on-the-fly adjustment.
Charge current and I²C programmability
The 300 mA maximum charge current targets small-capacity Li-Ion cells typical in wearables, hearing aids, and IoT end-nodes. The constant-current, constant-voltage profile is standard for Li-Ion, but the I²C interface allows the system MCU to adjust the charge current dynamically — useful for thermal management or charging from a current-limited source. Over-voltage fault protection is built in; no external blocking diode is needed if the input voltage stays below the 5.5 V supply max.
NRND — plan for a replacement
That means TI is not actively promoting it for new projects, though it remains available for existing production. For a new BOM, look at the current-generation BQ2512x family — the BQ25120A or BQ25125 are the natural successors with similar feature sets and pin compatibility.
Package and field handling
The 25-DSBGA package is a 0.4 mm pitch wafer-level chip-scale package. No lab, no bench — but you do need a hot-air station or reflow oven with a fine-tip stencil to place it. The solder balls are on the bottom; orientation is marked by a corner dot on the package top. ESD-sensitive, so keep it in the conductive foam or tape until reflow. The tape-and-reel delivery is standard for pick-and-place.