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AMC1350-Q1: DC voltage measurement with resistive divider

Leandro Stamm
Prodigy 10 points
Part Number: AMC1350-Q1
Other Parts Discussed in Thread: AMC1350, AMC3330, ISO224, AMC1351

Hi,

I'm trying to perform a DC voltage measurement with the AMC1350, but I'm having some difficulties:
I have a resistive divider to measure a DC voltage link. I would like to measure the voltage across one of the intermediate resistors of the resistor divider (a resistor that is not present at the edges/ends of that divider).
Employing the AMC1350, for some reason I could not perform the measurement on an intermediate resistor that I would like to do. The AMC1350 only measured the voltage when I replaced the resistors at the bottom with a short circuit (so that the resistor where the measurement takes place was connected to the negative pole of the DC link).

The figure below illustrates what I said:



All the documentation I found indicates to connect GND1 to the negative side of the measured voltage, without a resistor.

Would it be possible to use the AMC1350 in my first setup (without the short circuit)?
If yes, how? If not, why not?

Thank you in advance,
Regards.

  • 0
    TI__Mastermind 47695 points

    Hi Leandro,

    In the schematics provided, there is no GND1 connection to the negative side of the measurement resistor to ensure that the input voltage remains within the input voltage common-mode range. 

    I recommend a schematic similar to what is shown in this document: https://www.ti.com/lit/an/sbaa553/sbaa553.pdf

    Keep in mind that the isolated power supply must be referred to this floating ground connection as well. If measuring 3 phase voltage, then using a single isolated supply referred to neutral with 3x AMC1350's may be more economical than 2 Line-Line measurements using 2x isolated supplies and 2x AMC1350's. 

    You could also consider AMC3330 (integrated DC/DC converter) or ISO224 (wider +/-12V input voltage range). 

  • 0 in reply to Alexander Smith
    Prodigy 10 points

    Hi Alexander,

    Thanks for the reply, but it didn't solve my question.
    As you wrote, it is really necessary to connect GND1 to the negative side of the resistor and I am doing it (I forgot to put it in the simplified figure that I sent earlier, sorry, the correct figure is below).

    So, would it be possible to perform voltage measurement with the AMC1350 for the setup in the first figure (with resistors in the path between the negative terminal of my DC link and the INN-GND1 connection)?
    I only want to perform a DC measurement in this application.
    It may be that another component can be used in the measurement I mentioned (for example, the aforementioned AMC3330 can, as is even illustrated in its datasheet, as indicated in the figure below), but, considering other factors, I would like to use the AMC1350 specifically (if possible).


    Thanks and regards,

  • +1 in reply to Leandro Stamm
    TI__Mastermind 47695 points

    Hi Leandro,

    Yes this is fine, just make sure that the isolated power supply is referenced to the same voltage node. Also, AMC1351 may be a better fit if only sensing DC. 

  • 0 in reply to Alexander Smith
    Prodigy 10 points

    Hi Alexander,

    Thank you for the reply, and for the suggestions of other components.
    It turned out that the issue I was having was actually related to some coupling issues. The voltage measurement circuit is working as expected.

    Thanks and Regards,

  • 0 in reply to Leandro Stamm
    TI__Mastermind 47695 points

    Happy to help and glad to hear the issue is resolved!