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AD4003 negative output


I am using AD4003 ADC in one of the design. In this we are using 3-wire turbo mode.

Clock frequency used is 100Mhz.

Now when I provide 3V differential signal to the input of ADC. I am getting a hex value 0x2D0CD which is near to -3V(Read on SDO line).

My question is why I am getting output of ADC with sign reversal?



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  • Thanks Rohit.

    You are using VREF = 5V, correct?

    If so, then the Common Mode Input Range specification is being violated and would explain why the output code is invalid.

    The common mode input range spec refers to the average voltage between IN+ and IN- pins. Nominally the common mode input voltage should be VREF/2. For 5V VREF this would bee 2.5V.

    For the 3V and 0V configuration above, the common mode input voltage is 1.5V, which is out of the min/max spec range in the data sheet.

    Achieving this common mode input voltage requirement can be done with devices such as fully differential amplifiers (see ADA4940, ADA4945, etc.)

    Alternatively, the AD4002 is a single-ended version of the AD4003, where the IN- input can be tied to ground and there are no common mode input voltage requirements (since it's not a differential device).



  • ok thanks I will check and solve this issue.