Post Go back to editing

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.

on Apr 18, 2017 10:19 PM

Need to see schematic

What else is on SPI bus??

Zoom in with analog scope;  analog of digital oscillation?

SCLK frequency?

Number of layers in pcb?


  • 11. A pair of inputs of the ADC will be dedicated to remote measurement over battery, while the cathode is ground. Thus, the negative input of the ADC will be close to the ground level. Is it alright or, perhaps, ot make sense to raise the voltage on the negative input?

  • 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.



  • Hi, I have an issue here.

    I built my measurement system on PCB that uses AD7175-2. As part of the verification I tested the ADC for noise performance. In particular , for testing differential measurement the following circuit was used (minimal presentation). The MAX5318 DAC was set to 1.23 V and 10000 Samples were taken

    I wanted to compare single conversion mode vs continious conversion mode and external vs internal reference. I got following results,The results are actually very good. But the single conversion conversion mode is spoiled by the fact that it took ~100 conversions to stabilize. I don't think it has something to do with the mode, but rather with the fact it was the first test to run.

    The question: is a such long settling time (?) normal?

    The settings of the ADC:

    3 channels running

    On all channels:

    input buffers enabled, reference buffer disabled, SINC5 filter, ODR100

    One more issue regarding the data sheet. The use of term "single-ended"  in the data sheet is misleading. Those are in fact pseudo-differential and should be called as such.

    Thank you

  • This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin