Lithium Polymer Batteries are a very common source of power today. Many electronics gadgets have one inside, and they have some reasonable features. I've bought great batteries, with different sizes and capacities for my electronics projects. So long I'm using this batteries, coming the problem: charge them.
According to
datasheet, MAX1811 is specifically made for USB devices. The minimum voltage to a common USB-powered device may be as low as 4.35V when cable and connector drops are considered. The MAX1811 is optimized for operation at these low input voltage levels. But USB hubs may also provide as much as 5.5V!. At high input voltages (5.5V) and low cell voltages (2.7V), the MAX1811's thermal loop may limit the charge current until the cell voltage rises.
My design uses 500mA was charging current (pin 2 - SELI - pulled up), but MAX1811 only taken this current if the device is a USB powered source. The other parts are two very common tantalum capacitors and a
LED for charging indication. LED is ON on charging state, and OFF when it's end.