USB power bus is a great source for charging a single-cell Lithium-Ion battery. This circuit shown you how to build a USB-powered single-cell Li-Ion battery charger using National Semiconductor s LM3622 Li-Ion Battery Charger Controller.The battery-charger circuit is designed to operate as a high power USB function. To be compliant with USB Specifications (Rev. 1.1), a high-power function must not draw more than 500 mA from the bus during normal operation. The LM3622 uses the 0.25 current-limit resistor R1 to set a 400 mA maximum charging current. This leaves a 100 mA surplus that can be used to supply USB control circuitry and other functions in the device.
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