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BQ76925: Alternate Connections for 3 cells battery

Dzianis Yaskevich
Prodigy 10 points
Part Number: BQ76925

Hello.
I want to use BQ76925 with a 3-cell battery and a built-in 3V3 regulator with an external transistor.

I expect 10mA current consumption on the 3V3 rail. If I implement the typical circuit from the datasheet, I will have 100 Ohm in series, leading to a VBAT voltage 1V lower than the top cell.

According to section 8.3.2.2.2 of the datasheet, only the top-cell amplifier (VC6 – VC5) can function with such a voltage difference.

So I would expect I need to use Alternate connection described in Table 1.


For some reason, only 5 and 4 cells batteries are described in this table. Can I use such an alternate connection for 3 cell battery?
it would be connected as described below:
Cell-3 VC6 - VC5
VC5-VC4-VC3-VC2 shorted
Cell-2 VC2 - VC1
Cell-1 VC1 - VC0

If for some reason this is not allowed, I can also imagine the following connection.


Please, suggest the preferred alternative connection for a 3-cell battery that uses a 3V3 regulator.

  • 0
    TI__Expert 5645 points

    Hi Dzianis, 

    I do not see a problem with your first proposal for 3-s, and it should work as mentioned, with top cell and the 2 bottom cells connected to real cells, and the intermediate shorted to the top. For the second proposal, the device might not work as expected, as the control loop is expecting a certain Rvctl drop towards BAT to be able to back-fed the LDO with the external FET, so I would recommend to just follow the initial idea. 

    Best regards, 

    Arelis G. Guerrero 

  • 0 in reply to Arelis Guerrero
    Prodigy 10 points

    Thank you Arelis,
    It would be great to see this table extended in the next revision of the datasheet to include the case with 3 cells.
    I will follow your advice and use VC6-VC5 amplifier for the TOP cell in the 3-cell battery.