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ISO7342FC: Input voltage below 3.3V

Alfred Logico
Expert 4170 points
Part Number: ISO7342FC

Hi Team,

My customer is getting failures on the ISO7342FCDWR IC.

Pin 14, 13, 12, and 11 are directly connected to an MCU and problematic chips have pin 12 voltage lower that the expected.

It is being used for UART communication.

I attached a good response on a good chip and a bad response on a bad chip.

From the waveforms, the good chip is at 3.3V level while the bad chip is only at 2.5V (channel2)

Channel 1 is pin 13. Channel 3 is pin 11.

 Good chip:

Bad Chip:

Here is their schematic:

Here are the tests they have done:

  1. I noticed that there is no UART response and saw that the pin 12 input has lower amplitude ~2.5V.
  2. I lifted pin 12 on the Isolator and the signal from the MCU now reaches 3.3V.
  3. I replaced the Isolator with a new one, and the signals are working perfectly.
  4. I again, changed the Isolator on the same board with the bad Isolator and took the waveforms I sent to you which is still ~2.5V.
  5. Then again, changed the Isolator on the same board with the known good Isolator and took the waveforms I sent to you which are at 3.3V.

Do you have any insight why this is happening to our part?

Thanks!

Best Regards,

Alfred

  • 0
    TI__Mastermind 49445 points

    Hi Alfred,

    Thanks for sharing the details related to the customer issue.

    It seems to me that the device pin 12 is partially damaged either due to ESD handling prior its usage or maybe over-voltage/under-voltage at pin 12 causing damage to some parts of the input circuit of the channel. Because of this, the input channel is probably consuming more current than what MCU can support, leading to a voltage drop on the MCU output.

    Do you know when did customer start seeing this? Did this particular sample start behaving like this after any EMC test (like ESD, EFT, Surge, etc.)?
    Please do share more information on when exactly this started happening. Apart from the reasons I have listed above, I do not see a reason why the input voltage should go to 2.5V.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    TI__Mastermind 49445 points
    Hi Alfred,

    Were you able to find out any more information on the issue that customer is facing?
    In case if the issue is addressed, please do let us know so that I can go ahead and close this thread. Thanks.


    Regards,
    Koteshwar Rao
  • 0 in reply to Koteshwar Rao
    TI__Mastermind 49445 points
    Hi Alfred,

    I am hoping that the customer was able to root cause the reason why MCU output / ISO input is going to 2.5V. I will go ahead and close this thread, if you do have more inputs please respond back to this post. Alternatively, you can also create a new post if the issue is different. Thanks.


    Regards,
    Koteshwar Rao