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BQ79614-Q1: Top Cell Balancing FET not fully biased

Yuveer Naraindass
Prodigy 20 points
Part Number: BQ79614-Q1

Good day 

I am currently facing an issue with my BQ79614PAPRQ1 BMS IC, 

note, I am only using 8 cells, VC* and CB* 9 to 14 are connected to VBAT. 

The cell balancing works perfectly for cells 1 to 7 but the external FET controlling the balancing of cell 8 does not turn on fully, 
it partially turns on after the rest of the pack reaches its  VCB_DONE_THRESH value.

I have also noticed that the FET stays on (partially) even after it reaches its VCB_DONE_THRESH. This takes much longer compared to the other cells, 

I have attached the Cell balancing network, 

Please could you assist with possible solutions or areas to explore. 

Thanks 

  • 0
    TI__Expert 8526 points

    Hi Yuveer,

    In order to help troubleshoot your problem, I will need a bit more information.

    First, the attached screenshots are cutoff at inconvenient locations.  Could you please send the pdf of your schematic so I can see the whole thing?

    Second, you stated that the cell 8 external FET was behaving abnormally and only partially turning on as well as refusing to completely turn off.  Could you please send an oscilloscope capture of the abnormal Vgs voltage over time for the external cell 8 FET?  This will help determine quantifiably what is going wrong.

    Best,

    Andria

  • 0 in reply to Andria McIntyre
    Prodigy 20 points

    Hi Andria 

    Thanks for the reply, 

    Please see the attached schematic, unfortunately I can not provide you with a complete schematic, but the pdf contains the important information.

    I will have provide you with the Vgs capture later today. 
    Thanks
    Yuveer 

    BQ79614 - Limited.pdf

  • 0 in reply to Yuveer Naraindass
    TI__Expert 8526 points

    Hi Yuveer,

    Thank you for attaching more of the schematic.  What you provided in the pdf should be sufficient.  I look forward to seeing the voltage captures.

    Best,

    Andria