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ISO35: Fail Safe Mode

Part Number: ISO35

Hello E2E,

I have a question on the ISO35 for a customer.

Here is what they measure:

RE=high = disable R

-        Cable connect from A to Z and B to Y -> R =.265V

-        Cable disconnect A or B -> R=.265V

-        Shorting AB -> R = .265V

RE = Low = enable R (where all my tests went before) AND DE = Low

-        Cable connect from A to Z and B to Y -> R = High

-        Cable disconnect A or B -> R= High

-        Shorting AB -> R = High

 

RE = Low = enable R (where all my tests went before) AND DE = High

-        Cable connect from A to Z and B to Y -> R = High

-        Cable disconnect A or B -> R= High

-        Shorting AB -> R = High  

 

I can’t see any determination of open, short or idle. Any suggestions of what to do or what may be causing this?

Thanks!

Russell

  • Also, this might give a better description:

    The last email I did not correct for DE = Low which I did not test due to disabled TX.
    Here is the table I measured of using combination but did not tell me when is short, when is open.
    It only differentiate between good cable or bad (short and open). How can we detect difference in open and short? Thanks!

    Cable RE DE D R
    Connect Lo Hi Low low
    Short Lo Hi Low high
    Open Lo Hi low High

    Russell
  • Hey Russell,

    Sorry I accidentally clicked the TI Thinks Resolved... Please feel free to say this did not resolve your issue.

    Thanks for bringing your query to E2E. I believe the core of your question is "How can we detect difference in open and short?" by just looking at signals on 'side 1' (RE, DE, D, and R) of the device. Please correct me if my understanding is incorrect.

    I do not think this is actually possible to do with just 'side 1' monitoring. 

    It may be possible to do this using external circuitry - but this would probably require additional digital isolation channels. I found this Analog Applications Journal article that may be able to help.

    Could you give us more details about the application and why this is a requirement for your system?

    Best regards, 

    Dan

  • Hi Russell,
    I haven't heard from you in a few days. Were you able to resolve this issue yourself or do you require more assistance?
    Best regards,
    Dan