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BQ27621-G1: Random SOC change after the board reboot

AMB
Prodigy 100 points
Part Number: BQ27621-G1

Tool/software:

Dear Team,

We are implementing the application code according to the following flow chart and after every reboot this application code runs which sets the data memory parameters.

We have also change the data memory parameters according to our battery. Those we are successfully able to set. But now when we reboot the board sometimes we might get unexpected SOC.

Kindly find below test results:

After 1st reboot No variations in results retain the previous value 

Kept the device idle 

After 10 minutes reboot the board little variations in SOC is observed i.e. 2 to 3% drift 

Again put the device in idle state for 10min and reboot now the SOC jumps to 17% and retain its value in next reboot as per below screenshot.

 

Can you guide us to improve this SOC jump issues after the reboot.

  • 0
    TI__Guru 61516 points

    Please do not re-start the gauge every time you reboot the system. The algorithm is designed to track cell voltage over time and you interfere with this algorithm if you re-program the gauge every time the system boots.

    Restarting the gauge will always introduce an initial error as cell state can't be determined unless cell voltage is a true OCV.

    If you use the gauge as a pure system-side gauge which gets reset frequently (e.g. user replaceable battery that gets swapped out regularly), then you'll have to make sure that the gauge is configured before the system applies a significant load (>C/25 approx.).

  • 0 in reply to Dominik Hartl11
    Prodigy 100 points

    Hi,

    Not to restart the gauge means?

    Are you saying this using application code or via hardware. Can you elaborate this more

  • 0 in reply to AMB
    Prodigy 100 points

    Hi,

    Not to restart the gauge means?

    Are you saying this using application code or via hardware. Can you elaborate this more

    I just tried using firmware 

    First I run the application code for setting the data memory parameters for setting battery related information and terminal voltage.

    Then after reboot I run the another application code which can only read the data memory registers but unfortunately the registers are retaining their default values. So could not able to found the solution so that the gauge could not get restart after reboot

  • 0 in reply to AMB
    TI__Guru 61516 points

    The gauge uses a complex algorithm "DynamicVoltageCorrlation" which basically evaluates how measured cell voltage changes against a built in model of the cell. Any time you reset/restart the algorithm, you interfere with this process.

    The idea is to configure the gauge whenever a reset is *necessary* (e.g. the gauge was power cycled). It's a mistake to reset and re-configure the gauge every time your application/system boots up. I just wanted to bring this point across. If your wrote a driver that resets and configures the gauge every time your system boots up, then you will never get acceptable gauging accuracy (which includes SOC variation after you reset and configure the gauge).