Single-cell Li-Ion charger with USB interface
The Texas Instruments BQ24022DRCRG4 is a linear charge management IC from the bqTINY™-II series, designed for single-cell Lithium-Ion or Lithium-Polymer battery packs. It integrates a power FET and current sensor in a 10-VFDFN exposed-pad package (3x3 mm VSON), making it a compact fit for portable devices where board area is tight. The charge current is constant and programmable up to 500 mA maximum, with a programmable timer for charge termination. Input power comes through a USB interface, and the IC includes over-temperature fault protection.
The 500 mA max charge current sets the charge rate for a single 4.2 V Li-Ion or Li-Po cell. For a typical 1000 mAh cell, this gives a 0.5 C charge rate — a safe balance between charge time and cell longevity. The constant-current phase is programmable via an external resistor, so the designer sets the rate per the cell manufacturer's recommendation, not a fixed internal value. The 6.5 V maximum supply voltage accommodates USB bus power (5 V nominal) with margin for cable drop and transient overshoot. The linear topology means the pass element dissipates (Vin - Vbatt) × Icharge as heat; at 5 V input charging a 3.7 V cell at 500 mA, the package dissipates about 650 mW.