What the BQ24123RHLR does in a battery-powered design
The BQ24123RHLR is a constant-current, constant-voltage charger for 1 to 3 series Lithium Ion or Polymer cells, with a programmable charge current up to 2 A and a battery pack voltage of 8.4 V. It belongs to the bqSWITCHER™ family, which integrates a synchronous PWM controller and power FETs to minimise heat in the 20-VFQFN package. The input supply can go up to 16 V, making it suitable for 5 V USB or 12 V wall adapters without an external pre-regulator.
Charge current and cell-count flexibility
The charger handles 1, 2, or 3 cells in series, with the battery pack voltage set to 8.4 V for a 2-cell stack (the 3-cell termination voltage is higher, but the IC's 8.4 V rating suggests a 2-cell target; the 1-3 cell range covers 4.2 V to 12.6 V packs). Charge current is programmable via an external resistor, and a timer provides backup termination if the current taper doesn't complete within the set window. Over-temperature protection shuts down the charger if the die exceeds the safe junction limit, which is useful in tight enclosures with limited airflow.