USB to 7V4 Lipo charger - unknown controller

[trobbins]

I just got in a cheapo ebay USB to 7V4 Lipo charger with 3-pin connector for battery.  I was hoping to charge a 7V4 Lipo battery in a handheld device that just provides a 2-pin connector to the internal battery (2 cells in series).  Alas, it looks like the USB charger connects 5V to one 3V7 cell at a time and so separately charges the battery pack's cells, rather than charging the 2 cells in series (as per say a boost).  A quick reverse engineer of the charger circuitry is below.  Anyone have any ideas on the 14-pin controller IC being used, as some googling didn't show up this configuration of charger circuitry ?

I'll have to go looking now for a different charger to suit my device, but it was interesting to see what I think they were doing.  Initial checking on suitable chargers seemed to show two forms of battery module - one form with two cells where the mid-point connected to the 3-pin connector, and another form where an internal thermistor connected to the 3-pin connector.

[Twinstaged]

If you’re looking for a basic 2 pin 7.4 volt charger this dfrobot fits the bill. https://www.dfrobot.com/product-1713.html

[trobbins]

Ta, yes I'd seen that unit - just have to clarify shipping cost with them, as I'm not sure that it is free for one unit.

[mariush]

You may want to check out MP2672A : https://www.monolithicpower.com/en/mp2672a.html

It's a 4v .. 5.75v in, to 2 cells in series charger with selectable standalone mode and i2c controlled mode ( optional i2c connection to configure some parameters or adjust some parameters on the fly)

It has a boost regulator built in that creates the output voltage needed to charge the cell and can also provide this voltage (minimum around 6.7v as needed by cells to charge) on an output pin to power a system in parallel with charging the battery.

Yes you need to solder it to a board, but maybe you can find a cheap QFN to DIP that would be compatible with the footprint. It's a rectangular chip with 4 pads on two sides and 5 on the other sides so a bit odd.

[trobbins]

Thanks mariush.  My aim is to just find a commercial charger assembly, like the DFRobot board.

I had hoped that the initial charger shown in post #1 would be a boost converter, with the 3rd terminal used for NTC temperature feedback (which I could then mask), but alas no.

[NiHaoMike]

If you want to use it to charge a battery that doesn't expose the midpoint, have you tried adding capacitors where it expects the cell connections so that it will work as a charge pump?

[trobbins]

I'm unsure what the controller IC is, so have no awareness of how the charging is done, except that it 'looks' like a basic form of duty-cycle charging alog with current limit or constant current control.  As per many cheapo products, the main control IC is likely a clone or has fallen off the back of a truck with any marking erased.