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ISOW7841: Isow7841 Isolator with ADC and reference IC interface issue

Part Number: ISOW7841

Hello Everyone

I have used ISOW7841 inbetween microcontroller and ADC(ADC128s022) with reference Ic(LM4132-4.1V).When i measure the reference voltage it showing 4.35V but i am using 4.1V reference.I have attached the schematic for your reference.Schematic Prints1.pdf

14 Replies

  • Hi Ganesh,

    In the "Recommended Operating Conditions" for ADC128S the range of VD is restricted to the range 2.7V to VA.

    I suspect with VD=5V and VA=4.1V the reference may be being pulled up by currents flowing from VD to VA in the ADC128S.

    Yours,

    Alex.

  • In reply to Alex Ballantyne:

    Hello Alex,

    I tested the same circuits without isow7841 it works perfectly.i have given VD=5V and VA=4.1V.when i measure VA it is perfectly 4.!V.
    Shall i make the VD=3.3V and VA=4.1V with isow7841 that solve my issue?

    Best Regards

    Ganesh
  • In reply to ganesh sankara:

    Hello Ganesh,

    I'm not sure, but it's worth a try if you can regulate VD down to 3.3V for the ADC. I don't know why the ISOW makes a difference except that all the data inputs can be 5V too with your configuration.

    Yours,

    Alex.
  • In reply to Alex Ballantyne:

    Hello Alex,

    I tested with VD=3.3V and VA=4.1V reference ic but when i measure at VA=4.26V.I am confused.

    Best Regards

    Ganesh
  • In reply to ganesh sankara:

    Hello Alex,

    I tested with VD=3.3V and VA=3V reference ic but when i measure at VA=3.98V

    Best Regards

    Ganesh
  • In reply to ganesh sankara:

    Hello Ganesh,

    That is puzzling, your schematic looks good but your reference voltage is always higher than it should be, no matter what VD or VA you choose.

    I wonder what your SPI interface is connected to. Is the ADC enabled? Are you able to disconnect the reference from the ADC? If you do that is the reference output correct?

    Yours,

    Alex.

  • In reply to Alex Ballantyne:

    Hello Alex,

    SPI interface with Microcontroller.The same hardware design i have without ISOW7841 that works perfectly.and i Disconnect the reference from ADC the voltage is 4.25V the same voltage when connected to 4.1V reference IC.

    Should i test the option of VA=5V and VD=3.3V.

    Regards

    Ganesh.S

  • In reply to ganesh sankara:

    Hello Ganesh,

    Is 4.25V the voltage at the ADC VA pin or at the reference output? If it's the voltage reference output, I would focus attention there.
    Another thing to try is connecting GND to GND(A)2 if you can do that safely. Maybe there is some problem in the ground paths.

    Yours,

    Alex.
  • In reply to Alex Ballantyne:

    Hello Alex

    VA is at the Reference output. ADC and Reference are both connected

    I Tested connecting the GND and GND(A)2 but there no effect.

    Regards

    Ganesh

  • In reply to ganesh sankara:

    Hello Ganesh,

    Can you disconnect the reference from the ADC and see if the reference output is OK with nothing connected to it?
    If it is still not 4.1V then I think maybe the circuit is somehow not as you expect from the schematic, maybe a symbol error or loading error; I know you will have considered these things already...

    Yours,

    Alex.

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