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ISO7421: ISO7421 failure on one transmission

Tobias Hensle
Prodigy 95 points
Part Number: ISO7421

Hi,

I just got a claim from a customer regarding communication problems which is caused by a defect of an ISO7421.

The electronic environment is between -20°C and 25°C (it's truck trailer with built in refrigerator) and is sealed with a protection paint. Ground shifts are at a maximum of 70V.

Is there any known issue with this kind of isolators? Is it possible to send the device in to TI for further analysis?

kind regards

Tobias

  • 0
    Prodigy 95 points
    Edit: Sorry I forget to mention that only one transmission line is effected. The ISO7421 has two. Both sides are supplied with 5V.
  • 0
    TI__Genius 17100 points

    Hi Tobias; welcome to the E2E forums!

    Thank you for the additional context. There aren't immediate known issues to share about this isolator, but please allow me 3-5 days to investigate and follow up with you here.


    Thank you for your time,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Genius 17100 points
    Tobias,

    Is the affected transmission line the forward (B) or reverse (A) channel? How do you describe the failure?


    Thank you,
    Manuel Chavez
  • 0 in reply to Manuel Chavez
    Prodigy 95 points

    Hi Manuel,

    Thanks for the quick reply.

    It's just the forward (B) channel, the other channel (A) works.

    There's no signal transmission from IN to OUT anymore, it doens't matter if it's a high or low level at the input.

    Both supply lines are switched due to sleep current reduction.

    Regards

    Tobias

  • 0 in reply to Tobias Hensle
    TI__Genius 17100 points
    Hi Tobias,

    We are looking for more information on the failure event; please attempt to provide responses to as many of the following questions as possible:

    1.) Does the device function normally after a power cycle and then repeat the same fault on the forward channel, or has the forward channel stopped operating completely?
    2.) Did the device begin to fail after any EMC test? or when did/does the device failure occur?
    3.) How is the device input/output monitored?

    It will be helpful for us to know more about the system around the ISO7421 in use. Can you elaborate on the previous sentence: "Both supply lines are switched due to sleep current reduction."?


    I apologize for the delayed response and large amount of requested answers; we are trying to gather facts and be on the same page. I will await your response.


    Respectfully,
    Manuel Chavez
  • 0 in reply to Manuel Chavez
    Prodigy 95 points

    Hi Manuel,

    There's nothing to apologize ;)

    Regarding your questions:

    1.) The forward channel stopped operating  completely.

    2.) The device passed every automotive conform EMC test and passed the EOL test. The problem occured after sveral miles in the field.

    3.) What do you mean with input/output monitored? I measured the signal with an oscilloscope.

    About the system:

    It's a locking system for truck trailes with LIN communication. The device is separated into two sections(on the same PCB) a LIN and a Motor section.

    The maximum isolation voltage is 70.The µC Port Pin PC7 is used to switch the supply, the I/O of the ATMega168PA are capable of sourcing upt to 40mA, the ISO7421 needs 5mA max. Both Vcc1 and Vcc2 are switched.

  • 0 in reply to Tobias Hensle
    TI__Genius 17100 points
    Tobias,

    It seems the ISO7421 is set up correctly, and it may have been damaged during operation in the field. What happens if the failed device is replaced with a known good unit? Is this the only device that is not operating correctly?


    Thank you for your thorough response! I will await your next one.


    Respectfully,
    Manuel Chavez
  • 0 in reply to Manuel Chavez
    Prodigy 95 points

    Hi Manuel,

    Yes, I replaced the defect part with a new one and the communication between both microcontrollers works perfectly now.

    kind regards,

    Tobias

  • 0 in reply to Tobias Hensle
    Prodigy 95 points

    Edit: This failure just happend once until now.

  • 0 in reply to Tobias Hensle
    TI__Genius 17100 points
    Hi Tobias,

    Thank you for your response. May I contact you at the email on your my.TI profile? If you'd like to send the device to me for examination.


    Best,
    Manuel Chavez
  • 0 in reply to Manuel Chavez
    Prodigy 95 points

    Hi Manuel,

    Yes, that would be great to send the device in to you.

    kind regards

    Tobias

  • 0 in reply to Tobias Hensle
    TI__Genius 17100 points
    To all following this thread,

    The device will be mailed for testing and analysis, and In the meantime this thread will be closed. Updates and conclusions will be posted.


    Thank you for using E2E Forums,

    Manuel Chavez