Lithium-polymer batteries are an excellent choice for portable projects. They are relatively cheap, hold a significant charge, and last for a long time. The drawback with these batteries is that they require rather complicated charging protocols. You have to watch out for overcharging, undercharging, overheating, etc…
We are looking for a standard part to use in our projects, so we decided to do a roundup of open source lithium polymer chargers from SparkFun, Seeed Studio, and Adafruit. With the exception of Seeed, all the chargers are based on Microchip’s MCP738xx family of battery management ICs that come in SSOP and DFN packages. They handle all the charging algorithms and usually only require a single external capacitor.
Lithium Polymer USB Charger and Battery from SparkFun is a basic charger designed around the MCP73831 IC. A solder jumper changes the charge current from 100mA to 500mA. LiPoly Fast Charger, also from SparkFun, supports currents up to 1A. This design uses the MCP73843 IC driving an external mosfet that handles higher current.
Seeed is up next with their Li-Po rider and Li-Po rider pro charger/power supplies. They are based on the CN3065 battery management IC. The charge current is 400mA when a powerful enough source is available. One thing to note is that Li-Po riders are not chargers but compact portable power supplies that deliver 5V at 350mA. Battery voltage is converted to 5V through a switching step up converter. The pro version delivers up to 1A of current.
Adafruit’s USB/DC Lithium Polymer battery charger uses the MCP73861 IC. A charging current of up to 1.2A can be selected through a resistor. This IC has thermal protection. A standard 10K thermistor can be added to the battery to shut down charging in case of overheating. Their USB LiIon/LiPoly charger uses the MCP73833 IC, and is similar to the previus product. This one doesn’t have the DC IN jack populated, and the maximum current is 1A.
After looking at what everyone is using we are going to add the MCP73833 to our part box. It is cheap, has programmable current, and thermal protection through a thermistor. We also liked Seeed’s use of a dc/dc converter for portable projects.