ADS8688: when use OPA2209 circuit before ADC input, ADS688EVM shows Large error in ADC output

Prodigy 400 points

Replies: 1

Views: 94

Part Number: ADS8688

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!

By the way, when I direct input the signal to ADC input pin, there is not so much error.

Best regards


1 Reply

  • Hello Yunjing,

    Did you apply external high voltage power supplies (EXT_HVDD and EXT_HVSS) on J12 and J14? or did you just use 5V_SDCC from SDCC card?