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Original question:

ADC sourcing and sinking current

PGA970 ADC Input Range

Pournima Shankardas
Prodigy 100 points
Other Parts Discussed in Thread: PGA970

hello,

while i am working on PGA970 EVM i got ADC amplitude voltage is approx 3.012V on LVDT. As provided in data sheet as well as we discussed, range of ADC is 0V - 2.5V then how its possible the output of ADC will come upto 3V.

kindly know above.

Thanking you.

 

  • 0
    TI__Mastermind 31655 points

    Hello,

    Are you seeing the 3.012V shown on the ADC Capture page, or the ADC settings page of the GUI?

    Regards,

  • 0 in reply to Scott Cummins
    Prodigy 100 points

    Hello

    On both sides I m getting same answer, a quiet difference in ADC capture and ADC page settings reading like on ADC capture getting 3V and on ADC setting page getting 3.012V.

    Thank you.

  • 0 in reply to Pournima Shankardas
    TI__Mastermind 31655 points

    Hi Pournima,

    My only explanation for this is that I believe the voltage measurement shown in the GUI may be incorrect, or with some additional scaling factor that I'm not aware of. The best way to determine this would be to check the ADC code value and calculate the voltage based on that and the input range of -2.5V to 2.5V.


    Regards,

  • 0 in reply to Scott Cummins
    Prodigy 100 points

    Hello,

    Scott cummins

    1.  As Programming tips provided in data sheet according to that i have done all resister setting but my issue of output voltage is not getting set ( as getting 3V).  To solve that can u suggest proper setting of required resisters.  

    2. In output ( what we calculated  ) we are getting 50 micron error.  

     To make it 0 or minimize it what should we do.  

    3. I m getting only positive voltage

    ( as refarance voltage is -2.5v to 2.5v) then what about negative voltage.

    What's mistakes happening from my side plz let me know.

    We r checking it on PGA970 EVM module.

    Thank you.

    Pournima shankardas.  

  • 0 in reply to Pournima Shankardas
    TI__Mastermind 31655 points

    Hello Pournima,

    Just to confirm, in your latest post are you now talking about the DAC output? 

    1. Without any firmware programmed, the DAC output can only be set in reset mode, and by directly programming the DAC value registers as well as ensuring the output is actually sent to the output pin with the TEST_MUX_DAC_EN bit set.

    2. Is this output error with respect to the expected value given the DAC resolution and total output range, or is this a total error between your input and the expected DAC output? If this is the former, the DAC does have a non-zero temperature drift and nonlinearity.

    3. The DAC output is only positive, and the reference comes from the accurate internal reference or from a reference ratiometric to the external supply to the PGA970.

    Regards,

  • 0 in reply to Scott Cummins
    Prodigy 100 points

    Hello,  

    1. From last few days while working on PGA 970 EVM module i m not getting applied frequency.  

    i. e   if i apply 5KHZ  then i m getting only 1.93KHZ.

    2. By connecting LVDT probe no excitation takes place.  No changes in ADC  voltage as well as ADC Capture page.

    I used full bridge LVDT probe  of peter hirt T151F.

    Please let me know the solution.

    Thanks,  

    Pournima shankardas.

  • 0 in reply to Pournima Shankardas
    TI__Mastermind 31655 points

    Hello Pournima,

    1. Is this a new behavior? Before were you able to get an output at the frequency that you expected, but now it is much lower than your expected frequency?

    2. Can you share a diagram of how your LVDT is connected? Also, what are your AFE settings?

    Regards,