Standalone Linear Li-Ion battery charger with thermal regulation in ThinSOT application note (PDF!) from Linear:
The LTC4054 is a single cell lithium-ion battery charger using a constant-current/constant voltage algorithm. It can deliver up to 800mA of charge current (using a good thermal PCB layout) with a final float voltage accuracy of ±1%. The LTC4054 includes an internal P-channel power MOSFET and thermal regulation circuitry. No blocking diode or external current sense resistor is required; thus, the basic charger circuit requires only two external components. Furthermore, the LTC4054 is capable of operating from a USB power source.
I really like that one. With just two extarnal passives its really easy to use (four if you want to have a status LED). And it fits perfectly on a SOT23 breakout if you just need the charger.
Nice chip, indeed. Unfortunately not easy to find stocked – here I can get it only from Farnell (5 euro + VAT a pop) or Digikey ($3/pc + VAT + import duties).
I would rather use something like MCP73831 – costs about 50 cents, same sort of package, but only 500mA max charging current. Which isn’t too big deal in most cases – USB can only deliver 500mA max by default …
http://www.electroschematics.com/9937/3-7v-li-ion-battery-charger-circuit/