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INA226: Use of to measure current and voltage of + and - rails in an audio amplifier

Ian Legg
Prodigy 50 points
Part Number: INA226
Other Parts Discussed in Thread: INA3221,

Hello,

I am considering using the INA226 to measure the DC voltage and current on the positive and negative rails of an audio amplifier. The rails are +-42v and the current no more than +-5A. I'm aware that the Vbus is 36v maximum but the following TI Design by Mayrim Verdejo shows the INA226 working with a Vbus of -48V.

http://www.ti.com/lit/ug/tidu361/tidu361.pdf

Has anyone any experience of doing this, possible circuits and wiring as I'm not so experienced with analogue electronics these days? My expertise is in micro controllers!

Thanks,

Ian

  • 0
    TI__Genius 15760 points
    Hi Ian,

    Thank you for reading my TI Design! It definitely works great for the following VCM range: -8V to -50V but this design will not work for positive voltages.

    I think I might have an idea of circuits that might work for your application. I have a few questions:
    1. You need to measure Vbus, Current and Power? Or you only need to measure current?
    2. You need to monitor boad rails +/-42V or only one of the two?

    Regards,
  • 0 in reply to Mayrim Verdejo
    Prodigy 50 points

    Hi Mayrim,

    Thank you for your reply. Indeed I see that your design would address the negative rail but I wasn't sure if it could be adapted for the positive rail?

    To address your questions, yes I'd like to measure Vbus (rail voltage) and rail current but having power is optional, although nice and yes I wish to measure both the positive and negative rails separately. At the moment this is just for interest but using a micro controller I may use the information to shutdown the amplifier if excessive current is used etc.

    Thanks,

    Ian

  • 0 in reply to Ian Legg
    Prodigy 50 points

    Hi Mayrim,

    Obviously not sure of your current work load but did you see my reply to you above?

    Thanks,

    Ian

  • 0 in reply to Ian Legg
    TI__Genius 15760 points
    Hi Ian,

    I had an idea of modifying my design for positive rail but it would work only if you only needed to measure current and not Vbus and power. So this would not work for your application.

    Unfortunately we have not design yet a circuit that would work for both measurements + and -. We only TI designs that measure negative values (the one you reviewed) and another that measures high voltages (www.ti.com/.../TIDA-00528).
  • 0 in reply to Mayrim Verdejo
    Prodigy 50 points

    Hi Mayrim,


    Thank you for your reply. Maybe I am trying to do something a bit strange, although I guess it's just like monitoring a bench PSUs + and - rails for current and voltage? I did stumble on this hackaday project by Max which uses a INA226 or INA3221 to measure + and - current and voltage.

    https://hackaday.io/project/10398-luke-open-framework-multimeterlogger

    Assuming this is valid way of using these TI devices and if the circuit was modified to measure my ranges with my own software, would it be possible to wire two of them into the amplifier rails without issue?

    Thanks,

    Ian

  • 0 in reply to Ian Legg
    TI__Genius 14825 points
    Ian,
    I just looked over that Hackaday project and I see he's using the INA3221, and originally the INA226. As he says on the page, the INA3221 version has some creative use of the alert pins that create a kind of auto-ranging feature, but these fail when negative voltage/current are applied. So with that in mind, I looked at the original design with the INA226. I have to say, I'm not sure I get how it is configured to measure negative voltages.

    The INA3221 uses a voltage divider to reduce the V+ signal to something within the tolerances of the device, and the ratio of the divider is chosen by the alert-pins based on overload status. But that said, it still can't measure negative voltage. The INA226 has a separate VBUS pin solely for measuring voltage apart from current, and it doesn't support negative voltages either, so I'm a bit confused on the claims of that design.

    Back to just the devices, both will measure positive and negative currents so long as the bus voltage is above GND, like in a battery charging/discharging application. But as to measuring both a positive and negative rail with the Vbus pin below GND, I don't think it can be done with that product. If you were to scale the negative bus voltage way, way down, so it fits in the Vsense range of measurement, either +/-82mV or +/-164mV, and you measured the voltage between GND and GND-0.3, the abs max spec of the INA226, it might work, but I haven't tried this setup. Do you have an INA226EVM to play with?
  • 0 in reply to Jason Bridgmon
    Prodigy 50 points

    Hi Jason,

    Many thanks for your time and detailed response. Sadly my analogue knowledge is not so great these days but thank you for looking at the link I provided and for your findings.

    I think it's fair to say that either the INA226 or INA3221 would work perfectly if I had only wanted to monitor the positive rail and that for monitoring the negative rail TI doesn't have an easy solution, despite TIDU361 which clearly works for its intended application.

    To keep within my ability I will consider a potential divider on each rail (with an inverting amp on the negative rail) which I'll feed into A to D inputs on a micro controller, that will monitor the voltage. As for current monitoring I will probably use an ACS712, which I believe will work on the negative rail.

    Again, many thanks for your support and help.

    Ian