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BQ35100: The Accumulated capacity is negative

Cui Liu
Prodigy 60 points
Part Number: BQ35100

Dear Engineer,

Out product used the BQ35100 ACC mode to test the power consuption,but we found the accumulated capacity is negative but the spec is 0~4.29E9 and also not the 0uAH  when we read the accumulated capacity at the first time after we do the calibration through I2c bus; and then if we do the calibration for the second time after the system power off ---->power on again, this value can be changed and different board may have different  Initial capacity. Can you help to confirm what's the reason?Why the accumulated is not 0uAH and why it is negative. Our hardware desing follow the demo board.

The detailed information for our board as below:

1. Different board has different accumulated capacity after do the calibration through I2C bus for the first powe on 

2. The accumulated capacity is negative.

  • 0
    TI__Guru 52115 points

    We will take a look and get back to you.

    Andy

  • 0 in reply to Andy Liu (BMS)
    Prodigy 60 points

    Dear Andy,

    Do you have any update information for the above issue?

  • 0
    TI__Genius 10370 points

    Cui,

    The gauge will "accumulate capacity" when the GA bit is active after sending the gauge start command. It will commit this capacity to flash when the gauge stop command is received. I suspect after the calibration process is done you might be sending the gauge stop command. Depending on how long the calibration process takes would result in different values.

    It is also possible noise in the accumulator might be causing false amounts of current. 

    I would recommend sending the "New battery Command" after calibration is done. Calibration is not one of sections wiped when this command is sent.

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Prodigy 60 points

    Dear Eric，

    Thanks for your confirmation.

    I will try to use the "New battery Command" to check whether the used capacity is 0uAH when the system is powered on for the first time.

    But for the second questin:why the used capacity value is negetive which do not meet the spec mentioned(0~4.29E9), could you help to confrim this value again? Thanks!

  • 0 in reply to Cui Liu
    TI__Genius 10370 points

    Cui,

    Conceptually primary cells cannot see charge current since they are not rechargeable. However in ACC mode the gauge is able to accumulate charge in both directions. We do not block the current if it flows backwards since this information could be used by the host to determine a backflow issue. 

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Prodigy 60 points

    Dear Eric，

    Thanks for your reply.

    I didn't fully understand what your said. In our system, we used the non-rechangeable battery and only support discharge mode in ACC mode.

    and we found the charge accumulation in BQ35100 studio is also the negetive value which is the same with our system,  can we think the negetive value for the used capacty is correct?

  • 0 in reply to Cui Liu
    TI__Genius 10370 points

    Cui,

    Yes discharge current is a negative value. My point was if positive current does flow through the senseR the gauge will also accumulate positive value.

    Thanks,

    Eric Vos