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BQ76952: BQ76952 cell balance abnormal

Star Xu
Genius 9645 points
Part Number: BQ76952

Hi 

The customer design with BQ76952, the schematic as below.

They add 0.25A fuse in the cell schematic. but they found the fuse will burn in the random.

The second problem is the balance waveform abnormal. When enable one cell balance the waveform is normal. When enable multi cells balance， the balance waveform abnormal。

Attached the waveforms for your reference.

 

Please give some suggestions about these two queries.

Thanks

Star

  • 0
    TI__Genius 9645 points

    Hi

    Anyone update?

    Thanks

    Star

  • 0 in reply to Star Xu
    TI__Guru* 81034 points

    Hi Star,

    It looks like the balance current is set to around 130mA when the cell voltage is around 4.2V, so I do not see why the fuses are burning. I do see a couple of things in the schematic that are of concern:

    • The Zener diodes (D29, D23, etc.) across each cell will prevent the cell voltages from reaching their proper levels when balancing. 
    • I was looking at the datasheet for the MX3416 MOSFET. It does not show the RDSON at lower Vgs voltages (Vgs will be about 1 to 1.6V when balancing assuming cell voltages are around 3V to 4.2V). This could be an issue if the FETs are not completely on.

    When you enable the balancing, be careful not to enable balancing on adjacent cells. See the note on adjacent cell from the app report:

    Best regards,

    Matt