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BQ76940: 13 cell Configuration relation to cell balancing registers

Rudresh Kumar
Prodigy 80 points
Part Number: BQ76940


With respect to the datasheet i have understood that each cell can be balancing by using Cell balancing registers,

Each bits (D0 to D4) in the CELLBALx registers, corresponds to each cell from cell 1 to cell 15

In my case , Only 13 cells are connected as per the datasheet page no 42, VC14-VC13 and VC9-VC8 are shorted,

Query Description

1.For 13 cell configuration which two bits should be ignored in the CELLBALx registers

1.In order to balance CELL 9 and CELL 13 which bits present in CELLBAL x register should be used?

2.With respect to my understanding, bits CB10 and CB15 should be used? But it is not giving expected outcome

Please correct my understanding

  • 0
    TI__Guru 54715 points

    Hi Rudresh,

    The registers represent a physical mapping of the bits to the pins.  The part will measure all cells but is designed not to include low voltage cells in the UV comparison (see the threshold in the BQ76940 data sheet), but does not shift which bits are balanced based on that automatic UV configuration.  So balance bit CB15 in CELLBAL3 always controls the balance FET between VC14 and VC15 whether it is cell 15 in the  pack or cell 13 or some other cell based on the connection.

    1. For a 13 cell configuration as shown in table 26 of the BQ76940 data sheet, bits CB14 and CB9 should be ignored.

    2. Yes, CB10 (and VC10) should correspond to your cell 9 and CB15 (and VC15) should correspond to your cell 13. 

    It seems your description of connections and bits are correct..  When you write CB15 to "1" you should see VC15 and VC14 pull together with a 70% duty cycle for the balancing operation.  It should remain in this condition until the CB15 bit is cleared by the host.  Please describe what is not turning out as expected.    

  • 0 in reply to WM5295
    Prodigy 80 points

    Thanks for the clear explanation,

    During cell balancing it is mentioned in the datasheet that adjacent cells should not be balanced at the same time, It means i have to consider Cells correspond to CB8 and CB10 bits(similarly CB13 and CB15) are adjacent to each other and should not balance these cells at the same time, 

    Is my understanding correct?

  • +1 in reply to Rudresh Kumar
    TI__Guru 54715 points

    Hi Rudresh,

    You are correct.