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AMC1311EVM: Voltage @ VINP pin is more than calculated.

ArTzy
Genius 13999 points
Part Number: AMC1311EVM
Other Parts Discussed in Thread: AMC1311

Hi Experts,

Seeking your assistance on this query from Cx:

I am providing 2V to VINP pin via an external voltage supply i.e., from AC mains. I am using your formula to calculate the resistors value i.e., R1+R2+R3 = 1.14M Ohm for VTP1 = 230V & VINP = 2V.

I tried with two different values i.e., R1+R2+R3 = 1.142M Ohm & R1+R2+R3 = 1.153M Ohm. When i measured the Analog input voltage via Oscilloscope, i am observing 5V @ VINP pin when R1+R2+R3 = 1.142M Ohm & 4V @ VINP pin when R1+R2+R3 = 1.153M Ohm.

I have given oscilloscope voltage probe to J1.1 & oscilloscope voltage probe to J1.2. Please find the attached word document for the waveforms.

Regards,
Archie A.

AMC1311EVM problem.docx

  • 0
    TI__Guru**** 168895 points

    Hi Archie,

    Can you please clarify what the traces are in the document you attached?  What are the yellow and blue traces (CH1 and 2)?  Are they the outputs from the AMC1311?  With the equation from the users guide, R1, R2 and R3 should be 380kOhms.  One big point to highlight, is that the AMC1311 does not have a bipolar input voltage range, it is only rated for 0-2V.  You cannot put "AC" on the input without first level shifting the signal or converting it to a DC voltage.  I suspect that is the reason for the distorted signal on CH3 (AMC1311 is clipping), but I can't give you a reason for the odd voltage levels at the moment without seeing how things are actually connected.  J1.2 is the reference input (i.e. ground).

  • 0 in reply to Tom Hendrick
    TI__Genius 13999 points

    Thanks, Tom.

    Blue and yellow graphs are outputs i.e., VOUTP & VOUTN.

    Regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Guru**** 168895 points

    Have you kept the inputs above ground?  What results do you see with Vin kept between 0 and 2V?