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BQ27742-G1: FET always opened, BQ off

Giuliano FRANCHETTO
Intellectual 380 points
Part Number: BQ27742-G1

Hi,

We are designing a board with a bq27742 to manage our LiPo battery. We have an issue with the protection FET, which is always opened, turning off the BQ27742.

I've seen on the forum that we can short one gate of the FET to kick-start the BQ. This works, but this solution can't be used when the product will be sold.

Our fet has Vgs(th) = 0.9V

Did I miss something?

Thank you for your help

Best regards

  • 0
    TI__Guru* 76230 points
    Hi Giuliano,
    The device once woken up from shutdown mode will remain turned on and will never go to shut down mode except power is cut off or the shutdown command is sent. To wake the gauge from shutdown mode, you apply a charge voltage on pack p and that wakes the device up.
    yOu are not supposed to short the gate of the fet. You have to enable IT (0x21) for the fets to come and make sure your checks sums for the protection are set correctly for the fets to stay on.

    Let me know if further clarification is needed.
    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 380 points
    Hi!

    During the first startup, when the battery is inserted for exemple, how should I apply the voltage to packp?

    The I2C should be disabled if packp is at 0, shouldn't it?

    Thank you for your help
  • 0 in reply to Giuliano FRANCHETTO
    TI__Guru* 76230 points
    Hi Guliano,
    This device is a pack-side gauge so it is not designed for the end-user to be the one inserted the battery. The battery is supposed to be inserted during production and a charger voltage applied to packp to wake the device from shutdown. Once woken it stays in awake.

    thanks
    Onyx