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BQ27742-G1: RC2 as interrupt pin not needed for i2c design?

Christopher Buckley
Intellectual 330 points
Part Number: BQ27742-G1
Other Parts Discussed in Thread: BQSTUDIO

Hello,

Looking at the two reference designs in the datasheet (figures 19 and 20 respectively) I'm wondering if there is some reason the RC2 pin is not connected in the i2c design? Is the intent that firmware should be polling this chip regularly, such that an interrupt pin is not required? If I do chose to use it as an interrupt pin using i2c and not HDQ, what kind of resistance should I put on the pin and to where (REG25? GND?) if I am planning to connect it to a GPIO on a microcontroller elsewhere? Is this pin normally held low and interrupt signaled by it pulling high or the opposite? Also what is the pulled up voltage? Is it the 2.5V regulator voltage? That'd be my guess from the Functional Block Diagram but I'd like confirmation.

Best regards,
Christopher

  • 0
    TI__Guru 57697 points

    Hello Christopher,

    RC2 should be functional in I2C mode unless there is a specific mention that it is not. The TRM has details on how the interrupt is configured. The connections would be dependent on the configuration.

  • 0 in reply to Shirish
    Intellectual 330 points

    Thanks Shirish.

    I had forgotten to check the TRM. The section mentioned is shown below.


    So I will plan to attach RC2 to an external pull-up resistor and pull it up to 3.3V to match my GPIO levels on my microcontroller. I would then configure this as [HOSTIEN]=1, [HOSTIPU]=0, and [HOSTIPol]=0 to make Active-low interrupts and no internal 1.8-V pullup such that RC2 only drawing power when actively interrupted. Did I understand that correctly?

    Also could you confirm that these are not the default values? It's not 100% clear, but it appears the default values are 0,0,0 according to this:



    Best regards,
    Christopher

  • 0 in reply to Christopher Buckley
    TI__Guru 57697 points

    Hello Christopher,

    Yes, that will work. Make sure that the voltages on the pins are within recommended range. Default values are specified in the TRM. You can also see the default values in bqStudio by using the "Import" button dropdown

  • 0 in reply to Shirish
    Intellectual 330 points

    Hello Shirish,

    Shirish said:
    Default values are specified in the TRM.

    Are they the values I screenshot in my previous reply? Those were the only relevant looking values in the TRM that I could find. The zeros look like they'd be the reset values by context, but this is not explicitly stated, so that is why I was requesting confirmation.

    Shirish said:
    You can also see the default values in bqStudio by using the "Import" button dropdown

    I unfortunately do not have access to a Windows machine at the moment, so if you wouldn't mind confirming these values via either the TRM or bqStudio, it would be much appreciated.

    Shirish said:
    Make sure that the voltages on the pins are within recommended range.

    Good call, it looks like it is max of 2.75V on the RC2 pin so I'll have to translate the 1.8V volt up to 3.3V somehow. Thanks for the reminder!

  • +1 in reply to Christopher Buckley
    TI__Guru 57697 points

    Hello Christopher,

    The default values are specified in Table 5-3. The one you showed are also probably default values, but i would refer to the table

  • 0 in reply to Shirish
    Intellectual 330 points

    Thanks for pointing it out Shirish. Yep, they appear to be identical.