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

  • In reply to Alex Ballantyne:

    Hello Alex

    I have tested the Reference Ic its Output is 4.09V exact and there is no problem in the Reference Ic.



  • In reply to ganesh sankara:

    Hello Ganesh,

    OK, that is interesting.

    The reference can only source current so it will drift to a higher voltage if a current flows into the output pin. The only place that can happen seems to be the VA pin of the ADC128. You've looked at different VA and VD combinations and you know this problem only occurs when the ISOW7841 is used.

    I think you are looking for an interaction between the ISOW and the ADC128 that causes the VA pin to move towards a higher voltage. I wonder if the SPI interface to the ADC is the source of that interaction.

    The ISOW outputs have logic high voltage values =VISO to will be ~5V in your case. The recommended operating conditions for the ADC128 state that digital inputs must be 0 to VA so in you case the digital inputs exceed VA and the internal circuitry of the of the ADC will probably try to clamp them to VA, maybe with a diode, to prevent damage.

    Maybe current goes from the digital inputs that are high to VA and pulls the reference high.

    I'm not sure how you can test this easily. Maybe operate the ISOW with VISO = 3.3V so the logic inputs to the ADC are limited to 3.3V and use a separate 5V supply for VIN to the reference for now to see if this is the problem.

    That will give you VD=3.3V and VA=4.1V at the ADC which meets the recommended conditions.

    Hope that is it, and you can try it out without too much trouble!

    Good luck,


  • In reply to Alex Ballantyne:

    Hello Alex,

    VD=3.3V and VA=4.1V at the ADC.But no effect at the ADC Reference voltage it is measured as 4.36V.



  • In reply to ganesh sankara:

    Hi Ganesh,

    Have you made any progress with this? I don't really have anything else to suggest...