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BQ77915: Cell balancing algorithm

Silvan Sommer
Intellectual 320 points
Part Number: BQ77915

Tool/software:

Hello Luis

As you can see and read in the image from the datasheet: 

Only the VC5 in the example starts with cell balancing because it's higher than the Vvbth Threshold. 

My question what happens to the cell VC2? This cell is below the Vcbtl threshold what happens then?

Thanks

Silvan

  • 0
    TI__Genius 17775 points

    Hello Silvan,

    Have you watched this video (Link) on the cell balancing algorithm yet? It can help explain the algorithm function in more detail and provides several helpful diagrams.

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Intellectual 320 points

    Hello Alexis

    Yeah sure I watched it, but they didn't explain my case in the video. This is why I asked that question?

    I am testing the cell balancing right now, but im still not getting it why it won't work.

    Here is a picture of all my cell voltages and ive drew a similar diagram like the one in the datasheet and I put my cells in there: 

    As you can see, Cell 13 is below 3.8V and all the other cells are even above the Vstep. So from what ive seen in this image:

    The cell above the Vstep voltage (in my case all cells except cell 13) should balance??

    Or am i understanding something wrong :) 

    Thanks for your help and happy weekend

    Silvan

  • 0 in reply to Silvan Sommer
    TI__Genius 17775 points

    Hello Silvan,

    As stated in the video, VC2 would not CB as the cell has not met the requirements to start cell balancing and should continue to instead rise, if charge current is present and there are no faults present. 

    Silvan Sommer said:
    The cell above the Vstep voltage (in my case all cells except cell 13) should balance??

    That is correct. 

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Intellectual 320 points

    Hello Alexis 

    It dont balance by me...

    Im using external FET's and ive connected parallel 100Ohm resistor and a LED to the Rcb resistor which is 3.6Ohm by me.

    Is it even possible to see the cell balancing visual with LED's or is the ton time of the FET's so short that we can't see it?

    Thanks 

    Silvan