Charging a Lithium Battery via USB

Thread Starter


Joined Mar 20, 2009
Hey everyone, i am looking into a project that i want to be able to charge a Seiko MS621FE-FL11E lithium coin 3.1v battery.

I will be using the 5v from the USB and convert it to 3.3v using the LM3940. However, i am not sure what all i need between the 3.3v and the battery itself. Is there some type of protection that is needed so that the battery will not explode? I would also like to incorporate an LED that flashes when its charging and also stays lit when charging has completed.

I've been looking at the chip MCP73833 but it looks to output (charge) with 3.7v. If that is ok to use with the 3.1v battery itself then i can omit the LM3940 and just use the MCP73833 chip with 5v to the output (charging) of 3.7v to the battery. It also has output for LED's to show status! Sound good?

Any help would be great! :)

Last edited:


Joined Jul 26, 2010
Not a clue without full specs on the recommended charging method for that specific battery. You may find that you have to limit the 3.7V down a little but that would probably throw everything else in the circuit off.

I also notice that Pin 8 is labeled THERM, sounds like a safety that shuts the charger down if the battery gets too hot.


Joined Nov 28, 2008
I've been looking at the chip MCP73833 but it looks to output (charge) with 3.7v.
That 3.7V output from the MCP73883 is NOT acceptable as the battery datasheet specifically mandate the use of constant 3.3V voltage, current limited charging method.

Unless you can reduce the output voltage of MCP73833, you'll need other solution.

Thread Starter


Joined Mar 20, 2009
Alright, well i looked into it more and decided to do this:

Using a Dantona LIR2032 3.6V/40mAh Li-ion Rechargeable Coin Cell
Using a Nordic nRF24L01+ chip to be powered. (the max says its max power is 3.7v)
Using the MCP73833 to charge the antona LIR2032 3.6V battery

nRF24L01+ datasheet with power specs:

Dantona LIR2032 3.6V datasheet:

MCP73833 datasheet:

From the datasheets, it seems doable to use the MCP73833 to recharge the 3.7v dantona LIR2032 3.6v battery. But i'm no expert so that is why i posted my idea here of using this after reviewing everything.

Please let me know if you see a danger/potential problem with doing this :)