ADD7746 - Testing/Measuring Multiple CDCs Simultaneously?

So looking over the datasheet and the evaluation board instructions, I see how you can test a single CDC.

For my project, I would like to use eight AD7746s. At first, it would seem erroneous to use multiple EVAL-boards.  But I also figured I would reach out to this community so I do not make any assumptions.

My first thought is connecting all the digital inputs (SDA, SCLK, bINT) together into one EVAL board.  But looking at the functional block diagram of the EVAL board, this will not work since the board only has one set of excitation outputs, EXCA and EXCB.

Is there an alternative approach, or is using 8 EVAL boards the worst case scenario?

Would it be cheaper / better if I just do a PCB layout that expands the EVAL board to the number of AD7746s that I need?

Thank you very much.

Allan

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  • Dear Eric:

    Thank you for taking the time to answer my question.

    Actually, there was a point when the AD7147 was considered.

    However, for our purposes, we need the best resolution, and the AD7746 provides 24-bit resolution down to 4aF.

    Also, for all the components you have recommended, there is only one excitation source output (SRC for AD7142/AD7143 and AC_shield for AD7147).

    Since our design involves having a capacitor matrix, there are multiple CIN+ inputs and SRC outputs that we would like to measure.

    As of now, we will be using one EVAL board to test each CDC one at a time.  But we would like to expand this design so that we can measure multiple outputs at a given time.

    Though it would look silly to have 8 separate EVAL boards hooked up to 8 computers to do these measurements, this seems to be our worst case scenario.  Is it possible to do this efficiently? Or any other suggestions?

    My initial thought would be expanding the current EVAL design to have more outputs, but that is also another worst case option.

    Thanks again.

    Best,

    Allan

Reply
  • Dear Eric:

    Thank you for taking the time to answer my question.

    Actually, there was a point when the AD7147 was considered.

    However, for our purposes, we need the best resolution, and the AD7746 provides 24-bit resolution down to 4aF.

    Also, for all the components you have recommended, there is only one excitation source output (SRC for AD7142/AD7143 and AC_shield for AD7147).

    Since our design involves having a capacitor matrix, there are multiple CIN+ inputs and SRC outputs that we would like to measure.

    As of now, we will be using one EVAL board to test each CDC one at a time.  But we would like to expand this design so that we can measure multiple outputs at a given time.

    Though it would look silly to have 8 separate EVAL boards hooked up to 8 computers to do these measurements, this seems to be our worst case scenario.  Is it possible to do this efficiently? Or any other suggestions?

    My initial thought would be expanding the current EVAL design to have more outputs, but that is also another worst case option.

    Thanks again.

    Best,

    Allan

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