AD7327: Control setting and Conversion Data read for "Fully Differential Input Mode" and "Pseudo Differential Input Mode"

Hi,

Couple of queries on AD3727

1. For setting 8 inputs as "4 Fully Differential Inputs" (Mode 1 = 1, Mode 0 = 0) or "4 Pseudo Differential Inputs" (Mode 1 = 0, Mode 0 = 1) whether user has to write 8 times Control Word with appropriate ADD2, ADD1 and ADD0 and corresponding mode bits or 4 times with ADD2:1 = 0, 3,4,7? Why i asked this question is that, if Mode is selected as AD, the analog inputs are fixed for ADD (0 and 1 ) or (2 and 3) or (4 and 5) or (6 and 7). 

2. Similarly what the Channel Identification number in DOUT while inputs configured Fully Diff or Pseudo Diff? 

with regards

Rajeeva GK

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  • +1
    •  Analog Employees 
    •  Super User 
    on Sep 14, 2021 6:53 PM

    Rajeeva,

    First of all my apologies in the delay in responding to this query as I've been trying to track down the answer from the design team.  Unfortunately I'm going to have to head to the lab and validate this for you (which may take a few days) but my expectation is as follows:

    1) In differential mode (MODE[1:0] = 2'b10 or 4ch Pseudo-Diff Mode (MODE[1:0] = 2'b01) , addressing the positive(+) input channel  (I.e. 0, 2, 4, 6 ) should provide you with the desired output voltage.

    2) I will verify with a setup in my lab but I believe an output code equal to the channel programmed will be returned with the result. 

    I should have a result for you in a day or two depending on availability of the hardware.


    Sean

  • 0
    •  Analog Employees 
    •  Super User 
    on Sep 17, 2021 3:19 PM in reply to @skowalik

    Rajeeva,

    I have verified that my assumptions from my previous post are correct but I will add that the following is true.  Regardless if you address the positive(+) or negative(-) channel of a given differential or pseudodifferential pair you will always get valid data for that pair AND the output channel will always indicate as the positive channel (0, 2, 4, 6).

    So to be clear if I were sampling differentially between channels 0 and 1 then regardless of where I set AD = 0 or 1 I would always get a conversion result that was equal to (Vch0-Vch1) and the channel indication will output 0.

    Hope that helps.

    Sean

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  • 0
    •  Analog Employees 
    •  Super User 
    on Sep 17, 2021 3:19 PM in reply to @skowalik

    Rajeeva,

    I have verified that my assumptions from my previous post are correct but I will add that the following is true.  Regardless if you address the positive(+) or negative(-) channel of a given differential or pseudodifferential pair you will always get valid data for that pair AND the output channel will always indicate as the positive channel (0, 2, 4, 6).

    So to be clear if I were sampling differentially between channels 0 and 1 then regardless of where I set AD = 0 or 1 I would always get a conversion result that was equal to (Vch0-Vch1) and the channel indication will output 0.

    Hope that helps.

    Sean

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