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BQ30Z554-R1: CB PF Happened

alec
Prodigy 175 points
Part Number: BQ30Z554-R1
Other Parts Discussed in Thread: BQ30Z55

Hi sir,

I have an old model design for new customer using bq30z55 2S1P

After 1 month sample test, customer returns 3 fail samples. the CB PF was active

CB PF trigger duo to delta cb time > 40h

my questions are

1. Why it happened so fast? only 16 cycles. the Qmax cell and cell voltage looks great

2. If Qmax cell 1 > Qmax cell 0, only cell 1 should be balanced right ? why cb time Cell 0 also has 84h?

3. How can I prevent this issue?

gg file after CB PF is attached

gg after PF.rar

 

  • 0
    TI__Mastermind 42535 points

    Hi Alec,

    CB failure indicates a failure in cell balancing. Cell balancing failure happens when the DOD calculated for one cell is higher than the other. So, if the OCV of the cell that's being balanced doesn't drop over the time that the balancing is turned on, it would have failed. That's what causes CB failures.

    It really doesn't have much to do with Qmax.

  • 0 in reply to Batt
    Prodigy 175 points

    Hi Batt,

    Thanks for your kindly reply!

    " Cell balancing failure happens when the DOD calculated for one cell is higher than the other "

    1. Where can I find DOD information?

    2. 2 cells in a pack, why the cell with lower DOD need to be balanced also ?

    3. Is there a right way to set CB Max Threshold and Delta Threshold parameter?

    4. Can you provide detail documents? I have to explain why the CB PF to customer

    Regards,

  • 0 in reply to alec
    TI__Mastermind 42535 points

    Hi,

    Please refer to the following videos, DOD stands for depth of discharge, it's the basis for our impedance track gauges.

    The cell with a lower DOD means it has higher charge than the other cell. So, the charge in it needs to be balanced down to the lower cell.

  • 0 in reply to Batt
    Prodigy 175 points

    Hi Batt,

    Thanks

    Let's simplify the question.

    In production line, we measure cell voltage difference within 5mV, impedance within 10 mohm and capacity within 1% and then make a 2S1P pack  

    How do I test to make sure these two cells make up a pack will cause CB PF in a short time?

  • 0 in reply to alec
    TI__Mastermind 42535 points

    Hi Alec,

    If you want to cause a CB PF, you need to have the cells highly unbalanced. Then you decrease the CB time/mAh to less than a tenth of what is set. Then you allow the cells to rest and charge. Once, charging starts the balance timer will be computed. At the end of it, if the cells are unbalanced, you will have the PF set.

  • 0 in reply to Batt
    Prodigy 175 points

    Hi Batt,

    Thanks

    Regards,