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Questions about AD7172/5/7-2

I have questions about AD7175-2, but I beleive they would also valid for AD7172-2 and AD7177-2, so the answers would be relevant for their users too.

  1. May the inputs be shared between the channels? E. g if Ain0 and Ain1 set up for differntial measurement on channel 0, may the Ain1 be used for single ended measurement on channel 1?
  2. I am a bit confused about dat rate and channels. if the data rate is 100 SPS, would it mean 50 SPS effective rate with 2 channels?
  3. For the reason of simplicity the ADC is to be used to measure following signals with full scale voltages:
  1.  +/- 1 V bipolar differential signal. (eg channel 0) 
  2. 5 V unipolar pseudodifferintal (channel 1)

The b) forces to use 5 V external refernce, which is disadvantageous for measurement on channel 1. Luckily, the ADC has inetrnal 2.5 V reference, which could be used on channel 1 to bring it closer to optimum range. Would it make sense to do so?

I may have further questions as I move on with the programming.

Parents
  • 7. What are the formulas to calculate gain from gain coefficient and offset code from offset voltage?

    8. What are exactly "internal" and "system" calibration? what is the difference? How exactly are they performed. The datasheet is not clear enough.

    especially

    System calibrations, however, expect the system zero-scale (offset) and system full-scale (gain) voltages to be applied to the ADC pins before initiating the calibration modes. As a result, errors external to the ADC are removed.

    Is confusing and vague and does not give clear instruction what should be done.

    9. what purpose is "((AVDD1 − AVSS)/5)" setting in the input selection?

    10. Do I suppose correctly that in unipolar mode the resolution is effectively equals 23 bit?

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  • 7. What are the formulas to calculate gain from gain coefficient and offset code from offset voltage?

    8. What are exactly "internal" and "system" calibration? what is the difference? How exactly are they performed. The datasheet is not clear enough.

    especially

    System calibrations, however, expect the system zero-scale (offset) and system full-scale (gain) voltages to be applied to the ADC pins before initiating the calibration modes. As a result, errors external to the ADC are removed.

    Is confusing and vague and does not give clear instruction what should be done.

    9. what purpose is "((AVDD1 − AVSS)/5)" setting in the input selection?

    10. Do I suppose correctly that in unipolar mode the resolution is effectively equals 23 bit?

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