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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.

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  • Hi,

    The absolute voltage on the analog input pins of AD7175 must be between AVSS - 0.05V and AVDD + 0.05V (un buffered) and AVSS and AVDD (buffered)  as per table 1 of the datasheet. If the analog input is outside this range, the ADC will still function but the part will not meet the datasheet specifications. So to answer your question, if AVSS=GND then it is okay to connect your negative input to GND as it is within the absolute voltage limit.

    Thanks,

    Jellenie

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  • Hi,

    The absolute voltage on the analog input pins of AD7175 must be between AVSS - 0.05V and AVDD + 0.05V (un buffered) and AVSS and AVDD (buffered)  as per table 1 of the datasheet. If the analog input is outside this range, the ADC will still function but the part will not meet the datasheet specifications. So to answer your question, if AVSS=GND then it is okay to connect your negative input to GND as it is within the absolute voltage limit.

    Thanks,

    Jellenie

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