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BQ76925: Vcout have 100mv error

Lina Wang
Intellectual 960 points
Part Number: BQ76925

hi sir,

my customer use bq76925 for the 4cell application, customer meet one issue as below :

when battery voltage as BAT0=3.318V BAT1=3.319V BAT2=3.318  BAT3=3.318, PIN15（VCOUT）(related BAT3 ) is bigger 100mv than other three cell VCOUT, 

what's the reason for this issue, why BAT3 VCOUT so big gap with other cell voltage, thanks.

Below is related schematic.

  • 0
    TI__Genius 10830 points
    Hi Lina ,
    Thank you for your interest in our products. A BMS expert has been assigned to your question.

    Regards,
    David
  • 0 in reply to David Hien
    TI__Guru 54715 points
    Hi Lina,
    Most likely it is due to the common mode effect of the input amplifiers. The part has stored calibration values for using all 6 cells. When reducing the cell count you can use the top cell as you have done and as mentioned in the data sheet, but the calibration for the top cell will not be as good. With a 100 mV error you will want to do your own calibration.
    The other option is to use the cells in sequence so that the stored calibration is good, but live with the limitation on the BAT voltage described in the data sheet section 8.3.2.2.2.
    Do note the part has a 10V abs max between BAT and VC6. The schematic shows the circuits for those pins coming from different connections. Be sure the part is not damaged.
    In your schematic it appears that the top of either C61 or C62 was intended to connect to BQ_VC1 Please check your connections.