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ADS124S08EVM: PGA Gin

John Boecker
Prodigy 150 points

Part Number: ADS124S08EVM

I am running the predefined Current Measurement script on the ADS124S08EVM board.  5 mV is appplied across the current shunt resistor R78.  The mean reading on the Time Domain tab in the Analysis Engine is 15197 with PGA gain of 1.  With no input to J9 pins 2 and 3 (across R78) the mean offset is 127.  If the gain is changed to 2, the mean reading is 20612.  I expected something closer to two times 15197 or 30394.    Likewise with PGA gain of 4 I get 24170 and I expect 60788.  What am i not understanding?

  • 0
    TI__Guru 50605 points

    Hi John Boecker,

    Welcome to TI E2E forum.

    To help narrow down the cause, could you please confirm if a jumper is installed on JP13 of your EVM?

    If you are using the internal 2.5V voltage reference, the voltage values from the code are:
    • Code 15197 (Gain=1): ~4.5 mV
    • Code 20612 (Gain=2): ~3.07 mV
    Regarding your measurement of 5mV: was this value measured across R78 with a digital multimeter? Also, could you confirm if a precision DC signal generator was used for this test?

    BR,

    Dale

  • 0 in reply to Dale Li
    Prodigy 150 points

    I have been locked out of the e2e URL.  I am now in a private window.

    I take it I cannot reply to your email have have to use this site.   This is the third time i have tried replying.

    The jumper is on JP13 from center to ground

    I agree with your 4.5mV for code 15197 but I get 6.14mV for code 20612.  In the time domain window it says the reference is 2.5V.

    The 5mV is measured at the terminal screws of J9 that go across R78.  The 5mV is generated from a DC supply set to 00.50V and fed to J9 through a 10K resistor.  The measurement is made with a Fluke 87V True RMS DDM.