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BQ40Z60: Persistence of data and statuses during shutdown mode

Andreas_
Prodigy 40 points
Part Number: BQ40Z60


Hello,

I am currently working on a project utilizing the BQ40Z60 and we have noticed that the battery manager will not increment the cycle counter if our system is shut down and the manager is set to shutdown mode for some duration, before turning the system back on and waking the manager to normal mode to continue the cycle. This seemingly resets its progress of the cycle and as such if the manager enters shutdown mode often enough the cycle counter will never increment regardless of how many times the battery is discharged.

This has made us look at State of Health and Full Charge Capacity to help keep track of our cells. But the persistence of these values in relation to shutdown mode are not clear to us from the data sheet and reference manual, and testing them is much more difficult than the cycle counter. So we would like to ask if there is any list that could be made available on which data and statuses of the battery manager are affected by, or lost, if shutdown mode is entered. Or in the case that this is not available, if you could help us find out if State of Health and Full Charge Capacity specifically are determined in ways that are unaffected by the manager entering shutdown mode partway through a discharge cycle.

Best regards,

Andreas

  • 0
    TI__Guru* 76230 points

    HI Andreas

    When you say the system enters shutdown mode, is it the gauge that goes into shutdown. If the gauge goes into shutdown, there is no way to keep track of passed charge while in shut down. The passed charge is what determine the increase of cycle count. As long as the accumulated charge goes above the cc threshold, then cycle count increases by 1. Why will you be discharging the battery when the gauge is in shutdown? Are you bypassing the charge and discharge fets to do this?

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Prodigy 40 points

    Hi Onyx and thanks for your follow up

    We are not discharging the battery while the gauge is in shutdown mode, only while in normal mode before entering and after leaving shutdown mode.

    The case we have identified where the cycle count does not increase is when the battery (starting at ~100% level) is partially discharged during use, then the device is shut down by having the gauge enter shuthown mode (by smbus) which turns off the fets, finally the device is turned back on through the gauge and the battery is discharged to low (~5%) level.

    After having shut down the battery manager, the charge accumulated before the shutdown seems to be forgotten. If the device is run from full to empty without the pause where it is turned off, the cycle counter will increase as expected.

    As this behavious seems to be how the gauge works, we're primarily hoping to gain some insight if we can expect similar effects from this case on the State of Health and Full Charge Capacity values, or if they are based on values and measurements that are not reliant on the gauge staying out of shutdown mode.

    Best regards,

    Andreas

  • 0 in reply to Onyx Ahiakwo
    Prodigy 40 points

    Hi,

    Would just like to check if it is possible to get any further information on if State of Health can be expected to accurately be calculated in a device which is occasionally completely shut down? (i.e. battery manager is put in shutdown mode and no current drawn from the battery until the manager is put back into normal mode.)

    Thanks,

    Andreas

  • 0 in reply to Andreas_
    TI__Guru* 76230 points

    Unfortunately, we do not have such a device. The gauge has to be powered on to track SOH correctly

    thanks

    Onyx