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BQ79656-Q1: BQ79656-Q1 cell balancing configuration creates problem of measurement of cell voltage readings

Part Number: BQ79656-Q1

Dear TI Team,

we are using BQ79656-Q1 AFE for our project.  we are communicated with MCU by UART. we are measuring 16 cell voltages and 8 GPIO temperatures, Battery voltage, and Battery Current.

The problem statement is that when we enable cell balancing feature we are facing Cell voltage readings not working.

Please find the below logic using for Cell balancing.

  • Good morning,

    Thank you for reaching out to us.  When you say cell voltage readings not working, could you be a bit more specific please? 

    Do the registers go back to their reset value or go to zero? Is there an offset in the voltage reading? In your code, are you running Vcell readings concurrently with the cell balancing? 

    When using the Cell Balancing feature there may be an offset in the voltage readings as current is being pulled between the cells and device. This pull to balance the batteries may cause the reading to be off during the CB cycle. 


    Fernando Dominguez

  • good evening,

    Thanks for your quick response.

    cell voltage readings not working means register readings value go to zero. we are reading cell voltage readings with cell balancing and there is no offset we added. How to differentiate CB cycle offset with voltage readings.

    how to add offset in voltage reading when cell balance is in auto mode.

    Can you explain the procedure for reading cell voltages when we enable cell balance?

  • Good afternoon,

    When attempting to read the voltages during cell balancing (CB) is in place, it could result in abnormal values. We recommend pausing the CB and putting some delay to let the CB pins settle (with around 30ms) to get a more accurate reading of the Vcell voltages. Then resume the cell balancing.

    Fernando Dominguez

  • Good morning,

    Could I ask you to share the logic analyzer logs to debug further the issue. 


    Fernando Dominguez 

  • Cell Balance PauseTime DelayCell voltage read

    Dear Fernando,

    sorry for the late reply.

    Please find the attached screenshots for the above request. Still we are facing the issue.

    Please give your valuable feedback to resolve Cell balancing issue.

  • Good morning,

    No worries, thank you for the information. From the logs you sent I am assuming that the Orange is the RX side of the device, and the Red is the TX side, showing no response.
    Let's go back a step, are you able to wake up and auto-address the device properly? If you don't properly address the device, or devices (depending on how many you have connected in stack) then you will be unable to communicate properly with them. 


    Fernando Dominguez