IC to charge 11.1V li-ion batteries

Bobb Fwed

For a while our project has been using the MCP73862 to charge 7.4V Li-Ion batteries with great success.
Some changes in our project design now require a higher voltage. We want to move up to the 11.1V Li-ion. But I've had some trouble finding 11.1V battery charging/controllers. I'm hoping people on here can point me in the right direction.

I'd prefer a surface mount part, and I'd prefer it not to be leadleass (QFN / BGA).

Any help would be greatly appreciated!

Peter KG6LSE

Illl second a need to here ! .

LoopyByteloose

I did a lot of reading and pondering of multiple cell Li Ion battery chargers earlier this year and the issues are made more complex as you increase the number of cells in series. Two in series are easily doable, but three demand more control.

I suspect that it is all about excessive discharges that damage the cells ability to recharge. Charging does not seem to require as much control as the cells tend towards inherently balancing the charge between cells. But when you have a high rate of discharge, it seems the cell with the highest voltage position is depleted first.

Charge rates are easy to control because of the charger design, but discharge rates can easily be many times higher than charge rates.

Also, short circuit or un-monitored conditions are fatal. I let a kid use a couple of 18650s on a robot recently and they came back ruined as he forget to turn off the robot. It seems that regardless of how intelligent my charger is, I need to create a battery holder that will limit all cells to not going lower than their rated voltage.

Take a look at laptop technology. It seems to have migrated toward preferring battery packs that use two sets of parallel cells in series.

Bobb Fwed

The batteries we get have a built in protection circuit that prevent over-current and short circuit as well as discharging below the rated voltage. All I need is the charger.

Tracy Allen

Take a look at Linear Tech, LT1512 (available in soic8 or dip8, up to 1A) or LT1513 (DD-7 or TO220-7, up to 2A). They are SEPIC controllers meant for battery charging, and they offer constant current and voltage charge control. They are not highly integrated as the one you are currently using, in the sense that you have to handle termination and temperature externally, i.e., with a small MCU. But you asked for something not in a QFN/BGA!

Bobb Fwed

Well I said preferably, so if there is a really good option that is QFN/BGA I am open. I just figured if I could find a bunch of 7.4V, non-QFN/BGA chargers, why wouldn't there be a few 11.1V ones?
It's just that QFN/BGA cost a little extra to assemble, and a bit difficult for me to test them unless they are assembled.

Tracy Allen

Linear Tech has more options in their lineup.

The one I have experience with is the LT3652. It is promoted as an MPPT buck IC for charging batteries from solar panels. But it would not be limited to that, and the MPPT can be used to prevent excessive draw at the input no matter what the source. It is a 12-lead MSOP with thermal pad, or DFN. It does also integrate charge termination and temperature limits. They rate it as up to 2A, but 1A or less is a more practical target.

The way I started with the part was via their evaluation module for the LTM8062, which integrates the LT3652 and the inductor and sense resistor into a small package, yes, a BGA. The EVM has that mounted on a demo board set up as a self-contained charger for a 7.2V Li-ion battery. The voltage is set by an external resistor, so you could plausibly change it to 11.1V. They have the thermal issues well in hand with that demo board. It barely gets warm. The BGA is mostly thermal vias thru to two massive ground planes.