Single Lithium Cell Charger

Using the BQ24002 from Texas Instruments it is possible to build a simple and small charger module for single lithium-ion (Li-ion) cells. The device is available in a SSOP20 package and so does not require heroic assembly and soldering skills.
Individual cells are becoming available from the main catalogue suppliers, but a much cheaper option is to rescue cells from defunct notebook batteries. In most cases only a couple of cells are faulty and the others can still look forward to a long and useful life. A single cell is ideal for any equipment that needs a 3.3 V power supply, and will generally give a good operating life. The charger circuit requires a 5 V input, which can readily be obtained from a USB port or from any 5 V power supply.

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Characteristics

- Designed for a single Li-ion cell
- Suitable for all lithium chemistry cells with a final voltage of 4.1 V or 4.2 V (lithium-cobalt, lithium-manganese and lithium-polymer)
- Configurable 4.1 V or 4.2 V final voltage
- Input voltage from 4.5 V to 10 V (depending on charge current)
- Charge current up to 1.2 A
- Charge current configurable via shunt resistor
- Linear regulator topology
- Precharge function for deeply-discharged cells
- Charge status indicated by two LEDs
- Two package options: SSOP20 or QFN