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Original question:

INA3221: Bus and shunt voltage on a negative rail

INA3221: Vpu pin connection

John B
Intellectual 335 points
Part Number: INA3221
Other Parts Discussed in Thread: ISO1541

Tool/software:

I am using INA3221 in schematic to monitor the voltage and current with a negative power supply. I will use digital isolator between INA3221 and MCU. 

I am wondering about Vpu (16) pin of the INA3221. How do I connect it ?

I already connected Vs (4) pin to PCB Ground and the GND (3) pin of INA3221 is connected to -5 V in my schematic.

I think I need to connect a resistor between Vpu (16) pin and Vs (4). The Vs (4) is already connected to PCB Ground at 0 potential.   

  • 0
    Guru 317450 points

    Is this the same application as in the original question?

    What are the desired output voltages for low and high outputs? Do they go through the isolator?

  • 0 in reply to Clemens Ladisch
    Intellectual 335 points

    Yes, the same application. The Vpu (16) pin not discussed earlier. 

    The I2C digital isolater I will be using between INA3221 and MCU. 

    The digital voltage level at the PCB is 3.3 V. 

     

  • 0 in reply to John B
    Guru 317450 points

    What are the desired voltages for low and high levels of the power valid output? Does the power valid signal go through the isolator?

  • 0 in reply to Clemens Ladisch
    Intellectual 335 points

    The Power Valid (10) pin is digital output open-drain alert signal. The desired voltage level for MCU is 0 V low and 3.3 V high.

    I am considering ISO1541 as I2C digital isolator. 

    I have not found an isolator yet for Power Valid (10). The same is true for Warning (8), Critical (9) and Time Control Alert (13). 

    Would you recommend a isolator for these signals.

     

  • 0 in reply to John B
    TI__Expert 8215 points

    Hello,

    John B said:
    Would you recommend a isolator for these signals

    If you would like to use the Warning, critical, and time control alerts you will need a separate isolator for these signals. If you don't need any of these signals you only need to connect the pins to -5V and you can ignore them.

    John B said:
    I am wondering about Vpu (16) pin of the INA3221. How do I connect it ?

    If you would like to use it, generally you would need to connect VPU to VCC and connect PV through a resistor like you said. Then you would need to use a digital isolator to safely connect it to the MCU.

    There is also another option however: since the PV pin uses it's own power supply you can connect VPU to 3.3V directly and use a voltage divider to keep the output voltage within the safe range for the MCU, like so:

    Let me know if you have any more questions,

    Levi DV

  • 0 in reply to Levi DV
    Intellectual 335 points

    Thanks for quick reply. 

    One last question.

    According to the first page of INA 3221 datasheet, the four digital output signals, Power Valid (10), Critical (9), Warning (8), and Timing Control (13) are pulled up (connected to Vs through separate resistors). And the VPU (16) is connected to VS (4). I guess this is true for positive voltage and current measurement.   

    However, in case of negative voltage and current measurement, if we don't need to read the signals Power Valid (10), Critical (9), Warning (8), and Timing Control (13) through MCU, then don't we need to connect these signals to Vs (4) pin ? The Vs (4) pin is Ground and GND (3) pin is - 5 V. The VPU (16) is connected to VS (4) in negative voltage and current measurement the same way as in case of positive voltage and current measurement. 

  • +1 in reply to John B
    TI__Expert 8215 points

    Hello,

    If you don't need to read any of these signals it is simplest to just connect them to GND (-5V in your case) and remove the pull up resistors. The VPU pin can be connected to VS (0V in your case).

    Let me know if you have any more questions for me,

    Levi DV