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INA3221: Questions about digital output pins

Noman Paracha
Intellectual 570 points
Part Number: INA3221
Other Parts Discussed in Thread: TPS7A85A

Hi Guang,

I have started the schematic using this IC. I have a few questions regarding the Digital output pins:

1)      Can I leave the Warning and TC pins open as I don’t plan to use them or do I need to tie them to ground or terminate with a different impedance?

2)      What is the VPU voltage? Is it different than Vs?

3)      What is the purpose of RDIV in Figure 20 of the datasheet?

4)      I plan to connect LEDs to Critical and PV pins. Have other customers done that before? It should be ok to connect LEDs to these pins, right?

Thanks,

Noman

  • 0
    TI__Mastermind 27390 points

    Hi Noman,

    1)     You can leave the Warning and TC pins open, or tie them to ground. It doesn’t matter.

    2)     VPU is the pull up voltage for the power valid detection circuit. It accepts up to 26V. Therefore it doesn’t have to be the same as Vs, but can be.

    3)     RDIV in Figure 20 of the datasheet is to divide VPU (also labeled as Vs), if VPU is higher than 6V. Another purpose is to divide so that the PV pin voltage is compliant with downstream devices PV pin is driving. If VPU is less than 6V, or if PV is connected to a different low voltage source, there is no need for RDIV. 

    4)     It is ok to connect LEDs to these pins, in series with resistors. Keep the current at a few mA at the maximum, but this requirement should be easily satisfied.

    Regards, Guang

  • 0 in reply to Guang Zhou
    Intellectual 570 points

    Hi Guang,

    Thanks for your quick reply. Regarding #2, does VPU have any relationship to power valid lower or upper limit that are programmed into memory? I plan on setting lower PV limit to 1.75V and upper limit to 1.85V, given that my nominal desired Vbus voltage is 1.8V. Thanks.

    Regards,

    Noman

  • 0 in reply to Noman Paracha
    TI__Mastermind 27390 points

    Hi Noman,

    You’re very welcome.

    VPU is independent of power valid lower and upper limits. As long as VPU is over 2.7V, the PV register will be able to pass its value and set the state of the PV pin.

    You have the freedom to set VPU to any voltage from 2.7V up to 26V.

    Regards, Guang

  • 0 in reply to Guang Zhou
    Intellectual 570 points

    Hi Guang,

    I have connected VPU pin to Vs, which in my case is 3.3V. If I set power valid upper limit to 2.21V and power valid lower limit to 1.75V, will it work properly? I am essentially treating the PV alert as an overvoltage trigger. If my bus voltage exceeds 2.21V, I want to flag it as an over-voltage event and pull the PV pin high, which in turn will turn the green LED off (or I can also use a bidirectional LED that can go red). Speaking of high, what is the high voltage level of a digital output pin such as PV when it goes high? Does it go up to Vs (supply voltage)? My schematic is attached for your reference. 

    Thanks,

    Noman

  • 0 in reply to Noman Paracha
    TI__Mastermind 27390 points

    Hi Noman,

    Setting VPU to Vs will work. As you planned, it enables monitoring of the three bus voltages by setting power valid upper limit to 2.21V and power valid lower limit to 1.75V. Whenever any of the bus voltages falls outside this window, the PV pin will be triggered.

    The PV pin is an open drain output. When all bus voltages are within limits, the LED will be OFF; when any one or more fall outside the limits, the LED will turn on. You may want to use a red instead of green, because it is a fault condition when it lights up.

    Regards, Guang

  • 0 in reply to Guang Zhou
    Intellectual 570 points

    Hi Guang,

    I have finished schematic and layout work of a design that includes INA3221 and TPS7A85A and another LDO that is not from TI. What I would like to do is have you (or whoever the right person is) to review my schematic and PCB design files and provide feedback. I would like to avoid making any trivial or avoidable mistakes. Can you please let me know how to share these files? Maybe send you an email with these files as attachments?

    Thanks,

    Noman

  • 0 in reply to Noman Paracha
    TI__Mastermind 27390 points

    Hi Norman,

    I’ve sent a message, please respond through email

    Regards, Guang