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BQ29209-Q1: Random turn on Balancing

Part Number: BQ29209-Q1

Hello,I have issue: when I measure voltage between VC1 and VC1_CB, sometimes voltage occurs 1.4V, sometime is 0V, battery are balanced.
Any ideas?

  • Hello Audrius,

    What are the battery voltages? The datasheet recommends to pull the CB_EN pin high (to disable cell balancing completely) if the battery cell voltages are low (Below VDD = 6-V). 

    The recommended cell battery voltage for cell balancing are 6-V to 8.4-V between Cell 2 and GND and 3-V to 4.2-V for Cell to GND. This is described in Section 8.3.6 Cell Imbalance Auto-Detection (Via Cell Voltage).

    Best Regards,

    Luis Hernandez Salomon

  • Yes, CB_EN pin tie to GND, because we need balancing, battery cell voltages are 3.86V, it turns on sometimes when I start measure voltage between VC1 and VC1_CB.

  • Hi Audrius,

    Luis is out of office for the next couple of days. To me, it looks like cell balancing is active when you see the higher voltage on this pin since you should see IR drop across the CB resistor. Are you monitoring the cell voltages at the VC2 and VC1 pins when it is enabled to see if they differ by 30mV?



  • it is start balancing, then I touched CB resistor for measurement voltage across that resistor,sometime it is 0V, sometimes it is 1.4V for short time. Cells voltage is the same. Can it be some charge from tester, which start that issue?

  • Hello Audrius, 

    It is difficult to know what could be going on. If using real cells with a real charger, do you see any unintended cell balancing occurring?

    If you measure the voltages directly at the differential pins in the IC for the cells, is there any voltage difference when compared to the voltage measured across the cells directly? 

    Best Regards,

    Luis Hernandez Salomon