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AMC1350: unbalanced voltage measurement

beesetty rajesh
Expert 1055 points
Part Number: AMC1350
Other Parts Discussed in Thread: AMC3330

Dear Experts,

I am trying to use 3 no.s of AMC1350 to measure 3 phase voltage. Page 33 of data sheet shows a typical example to measure the 3 phase voltage, which is similar to my area of interest. I have a couple of doubts in this. I find the all three voltages are being measured wrt the neutral. Can the voltages can be measured across a unit of the resistor which is middle of the series network of a phase? In this case, the INN pin and GND1 pin cant be shorted because the signal would be a differential signal.

Next, the application illustrated in the datasheet is perfectly balanced. If the voltages are unbalanced, neutral voltage cannot be zero. so, the neutral cannot be connected to gnd, which is common for all the three ICs as shown in the figure. In that case, I doubt if that configuration works.

Regards,

Rajesh BN.

  • 0
    TI__Mastermind 47775 points

    Hi Rajesh,

    The issue with not shorting VINN = GND1 = Neutral is that there is a possibility of the input voltage drifting outside of the common-mode input voltage range of the AMC1350's. 

    I recommend measuring as shown in the datasheet and if necessary, an additional measurement can be made from neutral to PE to quantify the neutral voltage. 

    Another option besides 3x AMC1350 is to use 2x AMC3330 and measure two line to line voltages to derive the individual phase voltages: https://www.ti.com/lit/an/sbaa553/sbaa553.pdf

  • 0 in reply to Alexander Smith
    Expert 1055 points

    Hi Smith,

    Anyways I want to use three individual AMC1530s to measure three phase voltages due to several reasons. In this case, I have basically couple of doubts.

    Firstly, Can I measure the three phase voltages like the way it is mentioned in the link you provided? However, there is no information of INN connection to the GND1 in the configuration.

    Secondly, If the above can be done, can I use a single 5V DC power supply for all the 3 AMC1530s?

    Thirdly, Is it mandatory to connect the GND1 and INN pins? I didn't understand the explanation that is given in the pin description.

    Regards,

    Rajesh BN.

  • 0 in reply to beesetty rajesh
    TI__Mastermind 47775 points

    Hi Rajesh,

    INN is referenced to GND1 through the sensing resistor in the link I provided. There must be a return path for the input bias current from INP and INN to GND1, otherwise the input voltage will drift outside of the common-mode input voltage range of the device. 

    No, when measuring phase to phase, the GND1 connections of the AMC1350's would be out of phase, hence why using an AMC3330 with it's own integrated DC/DC converter is recommended.