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BQ76952: BQ76952 balance issue

Star Xu
Genius 9645 points
Part Number: BQ76952

Hi 

The customer test with BQ76952, the input resistance 1k has been modified to 100 ohm.

Using 16-cell active balancing, the voltage sampling period is 3ms, and the ADC sampling rate during balancing is one-eighth.

Only turn on the balancing of one battery at a time, and turn on the balancing of 1 to 16 cells in sequence.

After turning on the balance of cells 1-3, the voltage abnormality occurs. The voltage dbecomes normal until the balance is turned off.

The abnormal voltage data during balance is shown as below. Why does the voltage abnormality only occur on cells 1-3? Other series voltage normal during balance?

Attached the schematic and abnormal figure:

Battery voltage when balancing is not turned on

Turn on balancing of battery 1

Turn on the balancing of battery 2

Turn on the balancing of battery 3

When the software controls the balancing of the 13th cell (only the balancing of the 13th cell is turned on), the balancing of the 14th cell is also turned on. When the balancing of the 14th cell is turned on, read (0x0083 CB_ACTIVE_CELLS) value of 0 shows that the balancing is not done. Turned on, but reading (0x0085 CBSTATUS1) shows that the balanced runtime is counting?

Please help check it.

Thanks

Star

  • 0
    TI__Mastermind 25880 points

    Hi Star,

    For the behavior with the lower cells measuring incorrectly, one possibility is that the recommended maximum voltage between VC0 and VSS (0.5V) is being exceeded. We've observed in previous cases that exceeding this limit can cause the Cell 1 voltage measurement to drop significantly. I recommend capturing waveforms of the voltage at the device inputs to see if this is the case.

    For the behavior with Cell 13, is this behavior only when turning on Cell 13 balancing or does this occur with other cells or in other conditions? Are they sending the proper checksum along with the balancing commands? Do they have a Saleae logic analyzer capture showing this behavior?

    Regards,

    Max Verboncoeur