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BQ76952: How to allow a GPIO from a host MCU to both WAKE and SHUTDOWN the AFE?

Abhijith V Narayan
Intellectual 446 points
Part Number: BQ76952
Other Parts Discussed in Thread: TIDA-010208, TIDA-010247,

Hello experts,

I want to allow the MCU to both shutdown and wake up the AFE using the GPIOs of the MCU. Please tell me if the below circuits (taken from different ref schematics) are sufficient.

  • To shutdown AFE: (From TIDA-010208)

  • To Wake up AFE: (From TIDA-010247)

  • Here can you please tell me why all this extra circuitry is needed? I also see that the same circuit is used for RST_SHUT also. Is it because there's two AFEs that are stacked?
    • Also is this the Code Logic: Drive the GPIO high to turn on the BJT which will allow the TS2 to be connected to GND?
    • Is there a simpler way to make the AFE wake directly because all you have to do is pull TS2 low?
  • 0
    TI__Mastermind 42060 points

    Hello Abhijith,

    Yes, those two circuits could be used. Are you stacking to AFE's? If so, yes, with stacked designs the circuits are a bit more involved.

    Correct. As long as you pull TS2 low (with respect to its own ground) then the part can wake-up. Typically a pull-down switch is all it takes, which is shown for the upper device in the image you shared.

    For SHUTDOWN, the SHUTDOWN command can be used, or the RST_SHUT pin can be used.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Intellectual 446 points

    Hello Luis,

    No, I am not using a stacked design. I'm using a single BQ76952 device with a host MCU.

    I wanted to use MCU GPIOs to "do the action of pulldown" instead of using just a switch.

    Luis H. S. said:
    If so, yes, with stacked designs the circuits are a bit more involved.

    So I can have the same circuit as used for RST_SHUT (that is, a capacitor, a pullup and give to MCU GPIO with code logic to be pulldown when I need to wake the device) for the WAKE function as long as the design is not stacked right?

    Thanks very much.

    Abhijith

  • 0 in reply to Abhijith V Narayan
    TI__Mastermind 42060 points

    Hello Abhijith,

    For RST_SHUT, you can use a GPIO directly to provide a high signal to turn-off the device.

    For WAKE, you require the pull-down switch, typically a low-leakage MOSFET or BJT. This one may not work too well directly with a GPIO.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Intellectual 446 points

    Hello Luis,

    I see that this is the approach Ryan has taken in the circuit I shared above. Just one more clarification, what is the purpose of R89, R93 and D10?

    Thanks,

    Abhijith

  • +1 in reply to Abhijith V Narayan
    TI__Mastermind 42060 points

    Hello Abhijith,

    This is because it is waking up a stacked device. 

    Since your design will not be a stacked device, you would not require any of these. A 10-kOhm to pull-down TS2 instead should be okay. Like in the bottom IC of the TIDA-010247:

    R92 can just be 10-kOhms.

    Best Regards,

    Luis Hernandez Salomon