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ADS8688A: Large error exist in DC signal acquire, when connect the 2nd order filter of ADS8688A EVM before ADC input

Prodigy 390 points

Replies: 3

Views: 178

Part Number: ADS8688A

Dear team,

I am testing our ADS8688A EVM and my input signal is a DC voltage from 0V to 5V.

Use the input range of 0~5.12V,

connect the OPA2209 filter between input DC signal and ADC input pin. then the ADC output error is extremely larger: 2V DC Vin, ADC output 1.698V, as shown in following picture.

Here is some test results during debug.

The voltage in A0+ of J25 is 2V DC, but voltage in J8 pin is 1.69V, so the ADC input pin voltage is 1.69V.

So I think this error between 2V and 1.69V ADC output is come from OPA2209 circuit, but this is only a 2nd order LPF.

Can you give me some help on this issue? Thank you!

Best regards


  • Duplicate thread.

    Please see

  • In reply to Cynthia:

    Neither of the two thread get useful answer. Please help on one of this two question.

    Thank you !

  • In reply to Yunjing Wang1:


    Apologies for the late response and confusion due to the duplicate post

    The OPA2209 is a second order filter with a cut off of 22Khz, thus the DC input should be able to pass through.

    Were no components on the board changed previously?

    This filter is also available for channels 0-3. Would you test this other channels to see if the DC input is also attenuated?