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ADS124S06: ADC output oscillating

Part Number: ADS124S06


I am measuring differential voltage +-1v (always) using AIN4(+1V), AIN5(-1V) channels and to measure offset voltage I connected AIN3 and AIN2 to AGND. Now when I power-on my system, first I measure the offset voltage (AIN3 and AIN2) and then I switch to channels AIN4,5 to measure +-1V continuously. When I measure offset voltage with global chop mode enabled using channels AIN3, AIN2 my output is oscillating between 5LSBs (more or less) to 16777216LSBs(Max code of ADC). If I disable global chop mode I get around 80LSBs of offset and the output is not oscillating. My question is why my output is oscillating if global chop mode is enabled when measuring the AGND signal? This behavior is not seen if I measure +-1V with global chop mode enabled or disabled.

FYI: AVDD=+2.5V, AVSS=-2.5V
Reference: internal reference

  • Hi Adla,

    The ADS124S06 will output the conversion code in binary 2's complement.  So values very close to '0' may produce a code in the negative direction.  So you must make sure that you are analyzing the output code properly.  Full-scale positive codes will be range up to 0x7FFFFF and negative full-scale is 0x800000.  A code returned as 0xFFFFFF in decimal is actually -1 as a binary 2's complement value.

    If you are using a signed 32-bit integer as a storage value you must properly sign extend the value from a signed 24-bit to a signed 32-bit number.

    Best regards,

    Bob B

  • Thank you, Mr.Benjamin

    Now the problem is solved.