• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 46 subscribers
  • Views 378 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS124S08: Global chop in ADS124S08

YOSHIHIKO KURUI
Prodigy 60 points
Part Number: ADS124S08

I have a question about the offset removal function of the ADS124S08 when global chop is enabled.
If global chop is enabled, even if there is a large offset in the differential voltage input to the ADS124S08, is the offset removed by internal operation and can Gain be increased?

In cases where the differential voltage of the ADS124S08 is large, for example where there is a difference between the sensor voltage and the reference voltage of the sensor element, Gain cannot be increased significantly enough. Is the Global chop function effective in such cases?

  • 0
    TI__Guru** 113765 points

    Hi Yoshihiko Kurui,

    The global chop feature of the ADS124S08 removes the offset and offset drift of the ADC only.  The global chop will not remove any offset or offset drift of the connected sensor.  The global chop mode is described in section 9.3.6.5 of the device datasheet.  For each conversion result in global chop mode there are two conversions.  The first conversion is with inputs as connected to the ADC and the second conversion swaps the inputs internally and then averages the two conversions.  The end result removes any ADC offset/drift, but accurately represents the connected input voltage.

    There is a method to calibrate the system offset using the SYOCAL command.  Here you would connect the sensor with the differential offset at the point where the sensor would be considered to be at the '0' point.  When the SYOCAL command is issued, the value of the conversion result is stored in the OFC registers within the ADC.  The value is then subtracted from all following conversion results.  If global chop is enabled, then the value in the OFC registers is not used.  So you are not able to combined features.

    If the offset is very large, then the the input may become overloaded in which case you cannot get a satisfactory result.  Can you be more specific as to the input voltage range would be as well as the desired reference voltage?

    Best regards,

    Bob B