I have a data-logger project that needs to run from a 3-cell Lithium Polymer battery. It has 5v and 3.3v regulators to provide regulated power to the system.

I want to build the battery into the device so that it is all self contained. When the user plugs in the USB cable to download the data, I also want the battery to charge from the USB.

So I'm looking for a chip / circuit that can take the 5v USB as an input and boost it to the voltage (12.6?) necessary to charge the 3S lipo, and manage the charge. The system still needs to operate while charging. When USB is unplugged the system should run from the battery.


1 Answer 1


As options for three-cell Li-ion/LiPo charging, you may choose from

Alternatively, you may use LTC4007 (datasheet), however, this requires an input voltage of at least 6V, so you'll have to supply an in-between boost mechanism from the USB voltage of 5V.

  • \$\begingroup\$ Looking at the LTC4007 Datasheet, it is a buck converter so he would need to provide at least 13 VDC to the input of the IC. I did not check the rest on your list. This does not quite fulfill the OP's requests. \$\endgroup\$
    – justing
    Aug 24, 2012 at 15:22
  • \$\begingroup\$ @justing: Updated answer based on your observation. Verified the other ICs mentioned do fit requirement. \$\endgroup\$
    – boardbite
    Aug 24, 2012 at 15:59
  • \$\begingroup\$ Thanks for the answers. The BQ24105 looks interesting. A little more detail: I really only need about 6v for my 5v and 3.3v regulators, which 2S could provide, but it has to operate at near freezing temperatures (it won't be freezing when charging from USB). Given the voltage drop at that temperature, I think it would need the 3S pack. System needs about 120mA. \$\endgroup\$
    – MX21
    Aug 27, 2012 at 18:21
  • \$\begingroup\$ @MX21: Since you mentioned "near-freezing", just out of curiosity, may I ask what is the context of this application? I understand if it's confidential, but if it's just a personal project, perhaps you can clarify \$\endgroup\$
    – boardbite
    Aug 27, 2012 at 18:40
  • 2
    \$\begingroup\$ Near Space - ~100,000 feet altitude \$\endgroup\$
    – MX21
    Aug 27, 2012 at 18:44

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