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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 DOUT/RDY pin serves as a dual purpose. It functions as a serial data output pin to access the output shift register of the ADC and also operates as a data ready pin, going low to indicate the completion of a conversion. When power-up, ADC continuously converts and if /CS is low the DOUT/RDY pin pulses at a selected data rate. The default output data rate of AD7175 is 250ksps. So what you are seeing is actually correct.

    Thanks,

    Jellenie

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  • Hi,

    The DOUT/RDY pin serves as a dual purpose. It functions as a serial data output pin to access the output shift register of the ADC and also operates as a data ready pin, going low to indicate the completion of a conversion. When power-up, ADC continuously converts and if /CS is low the DOUT/RDY pin pulses at a selected data rate. The default output data rate of AD7175 is 250ksps. So what you are seeing is actually correct.

    Thanks,

    Jellenie

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