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ISO124: Input Impedance and Ground reference

Mike_3007
Expert 2055 points
Part Number: ISO124
Other Parts Discussed in Thread: INA146, ISO224, AMC1200

Hi everyone, this is Mike.

I have designed this circuit based on the datasheet of ina146.pdf and iso124.pdf

But I have some questions related to the ISO124

I think I have a problem in the input impedance of the ISO124 because of the INA146 feedback.

What do you think?

Also I think I'll have some problems with the signal coming with INA146 because of the ground reference, the voltage at the input, at JCA, es line to line, so it is a differential measurement, after the signal passes through the ina146 it has a ground reference. I get confused at this point. 

Thanks for all your help !

  • 0
    TI__Guru**** 168895 points
    Hola Mike!

    The input impedance to the ISO124 is only about 200K ohms. Is this a new project? Have you looked at the ISO224 as an alternative to the ISO124?
  • 0 in reply to Tom Hendrick
    Expert 2055 points
    Tom, Is the same project we have talked so long time ago, I did some other projects but this one, because of the generator spec and things like that, I have to wait for some advices and the electrical engineers. So do you think this circuit is not gonna work properly? what about a voltage follwer between the INA146 and the ISO124?, I promise you I will give send some photos of the real signals when this thing works hehehe
    Regards
    Mike
  • 0 in reply to Mike_3007
    TI__Guru**** 168895 points
    Hi Mike,

    In that project you were looking to use the AMC1200. Is this just another part of the system? The ISO224 is a new device with +/-12V inputs, but only runs on a single supply. It also has over 1M input impedance which might help out here in place of a voltage follower.
  • 0 in reply to Tom Hendrick
    Expert 2055 points
    Hi Tom,
    I was thinking to design, at least, four circuits for this project, in fact this is the first one, where I will use this INA146 and ISO124, the other three ones I will be using some other different opamps, that ´s why I was looking for some others, I do this in order to achieve the best performance in one of all those designs, because here we have some time, and i want to spend this time achieveing the best design, or at least, not the worst jejeje
    Regards
    Mike
  • 0 in reply to Mike_3007
    TI__Guru**** 168895 points
    Got it! Let me know how the testing goes.