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BQ40Z50-R2: Undrstanding initial activation of fuel gauge

Noam Levy
Prodigy 120 points
Part Number: BQ40Z50-R2

Hello, we are using the BQ40Z50-R2 fuel gauge in our design. The implementation follows the typical application shown in the datasheet. When powering the board for the first time, after waking up the fuel gauge it seems that all FETs are closed. If I understand correctly this is normal behavior because the wake up process includes a Reset which shuts down the FETs. Is that correct?

Does this mean that we need to instruct the fuel gauge to toggle the FETs every time we power the board? If yes, do we need to toggle all three FETs or toggling one would get things started and the others will be controlled by the fuel gauge?

Thank you,

Noam

  • 0
    TI__Mastermind 28440 points

    Hi Noam,

    You are correct in the fact that a reset will close all of the FETs. However, this reset is coming from the device going through a Power On Reset when the device is being powered on the first time.

    If you plan to change the FETs status manually, then the three FET commands below will allow you to do this:

    However, if you plan on the FETs being controlled by the gauge, then the singular command needs to be sent:

    Regards,

    Anthony Baldino

  • 0 in reply to Anthony
    Prodigy 120 points

    Hi Anthony, thank you for your answer. I see that by default the FET_EN is disables, so if I want the gauge to allow charging after reset I need to change the golden image so that the FET_EN will be set to 1, correct?

    A related question on getting the gauge ready for production, when (if at all) do I need to seal the gauge?

    Thank you,

    Noam

  • +1 in reply to Noam Levy
    TI__Mastermind 28440 points

    Hi Noam,

    You are correct. Since FET_EN is contained within a flash register, whether it is set by the programming of the .srec, or enabled using the command, this function should be enabled after reset.

    In regards to the sealing of the gauge, this should be done as the final step when the gauge is in production as a security measure so the parameters cannot be altered when sent to market.

    Regards,

    Anthony Baldino