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INA3221-Q1: PV alert clarification

Shih Stone
Prodigy 65 points

Part Number: INA3221-Q1

Hi,

When we connect one channel and two channels are reserved (floating), then we set config register to disable this two un-use channels.

We observed that PV pin is still asserted after set PV limit lower/upper register value to be suitable. Could you help to advise us what we’re missing? Thanks.

Beside HW change(add power rails to un-use floating channel), any method can enable PV function?

  • 0
    TI__Mastermind 34700 points

    Hello Shih,

    I think you highlighted the issue.  All unused channels must have the IN- connected to a valid power rail. 

    I believe if you verify the reading of the Vbus for unused channels then change the PV registers and retrigger a conversion you may be able to undue the PV flag.  The issue is with the floating pins determining the value of Vbus and if the PV registers give enough range to create a non-triggering value .  The parasitics of the board could make that VBUS voltage non-repeatable.  If you attempt this I would trigger a single conversion and make the PV upper value full scale and PV lower limit 0 and attempt the conversion.  Then make sure the unsused channels do not get converted again.  If this works this will need to be repeated at each reset.

  • 0
    Prodigy 65 points

    Hi Javier,

    One more question - why the upper and lower limit registers are not writing negative values to those registers?  The sign bit for each of those registers clears after we write a negative value.
    For example:

    POST /argo/0/i2c/0/addr/64/txrx {"val":[16, 220, 216], "rx":2}# upper limit register set to -9V
# reads back value of [92, 216]
    POST /argo/0/i2c/0/addr/64/txrx {"val":[17, 216, 240], "rx":2}# lower limit register set to -10V
# reads back value of [88, 240]
    POST /argo/0/i2c/0/addr/65/txrx {"val":[16, 220, 216], "rx":2}# upper limit register set to -9V
# reads back value of [92, 216]
    POST /argo/0/i2c/0/addr/65/txrx {"val":[17, 216, 240], "rx":2}# lower limit register set to -10V
# reads back value of [88, 240]

    For both registers it appear the sign bit (15) keeps getting cleared even if we write a negative value.

  • 0 in reply to Shih Stone
    TI__Mastermind 34700 points

    Hello Shih,

    The Vbus voltage is not valid below 0V.  The sign bit is not valid for the Vbus measurement.  My suggestion was based on what the value of your Vbus measured when floating in your system.  This value is unpredictable and will be dependent on board and parasitics.

  • 0 in reply to Javier Contreras4
    Prodigy 65 points

    Hi Javier,

    It's not floating. We have 0.9V apply to that channel, but we still can't change it to negative value.

  • 0 in reply to Shih Stone
    TI__Mastermind 34700 points

    Hello Shih,

    The Vbus voltage is not valid when it is negative that is why you cannot place a negative value there.

  • 0 in reply to Javier Contreras4
    Prodigy 65 points

    Hi Javier,

    Are you means one channel valid and two channel not valid cause we can place negative value there?

  • 0 in reply to Shih Stone
    TI__Mastermind 34700 points

    Hello Shih,

    The Vbus cannot have a negative input at all.  See datasheet below.

  • 0 in reply to Javier Contreras4
    Prodigy 65 points

    Hi Javier,

    What are the consequences or impacts if we keep the 3221_PV_N line low and un-use channel in floating?

  • 0 in reply to Shih Stone
    TI__Mastermind 34700 points

    Hello Shih,

    Normally no issue if floating but it the PV will not function.  I would recommend that future you connect unused channels (IN-) connect to other channels as suggested in the datasheet.  Also when floating the pin is not controlled and can be influenced by other signals.