• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 1 answer
  • Subscribers 33 subscribers
  • Views 1605 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ISO1050: How to Select Small Size TVS Diode in CAN Applications

user4499359
Intellectual 450 points
Part Number: ISO1050

Dear team:
Due to board size limitations, small-size transient suppression diodes are required. Do not know how to choose. Under the guidance of trouble.

  • 0
    TI__Expert 6195 points
    Hello,

    Thanks for bringing your question to E2E. I'm consulting with the rest of the team to make a recommendation for you. This may take us a bit. I'll update you with your progress by the end of the day tomorrow.

    Best regards,
    Dan
  • 0 in reply to Dan Kisling
    TI__Expert 6195 points

    Hi again,

    I have a couple of follow up questions so we can make a recommendation for a proper TVS for your system:

    1. How small is small enough for your application?
    2. Are you confident that the signals on the CAN lines will only be positive? If so, we can use a unidirectional TVS diode which will clamp at high voltage in one direction. Otherwise we will need to select bidirectional TVS diodes. 
    3. What are you hoping to protect against? EFT? ESD?
    4. What level of protection?

    Best regards, 

    Dan

  • 0 in reply to Dan Kisling
    Intellectual 450 points

    Dear team:
    My entire system is using ISO1050, are designed according to the following figure. I initially chose PESD2CAN, but I feel a little larger. My application may be at industrial sites, hospitals, etc. I'm not familiar with CAN protection and would like to hear your suggestions.

  • 0 in reply to user4499359
    TI__Expert 6195 points

    Thanks for including your schematic!

    PESD1CAN and PESD2CAN are commonly used, but they are not necessarily the best fit for ISO1050. 

    • The key thing here is to position the TVS/ESD diode breakdown voltage. 
    • It must be above the Operational range of the part (+/- 12V per the data sheet) so as to not interrupt normal operation, and also must be below the Abs Max (-27 V / +40 V per the datasheet) value ( = damage rating) of the part, so that the chip is not damaged.
    • When positioned this way, normal operation is uninterrupted. But when an ESD or other high voltage event happens, then the diode will trigger first and still protect the device. 
    • If the diode breakdown voltage is too high, then the ISO1050 may trigger first - which we don't want to happen.

    Let's set the breakdown to +/- 14 V as to not disrupt normal operation (> +/-12 V operational range). 

    Let's set clamp to +/- 20V to give margin to absolute max (-27 V / +40 V, but these diodes are usually made symmetrically so we'll have to spec to 27 V).

    Given these constraints I was able to find the following TVS that would suite the ISO1050. 

    Do any of these fit your size constraints for your application?

    Best regards, 

    Dan

  • 0 in reply to Dan Kisling
    Intellectual 450 points

    Thank you for your guidance, I re-elected SM712.

  • 0 in reply to user4499359
    TI__Expert 6195 points
    I just looked through the SM712 datasheet. Looks like a fine choice of TVS. One thing to consider, if you expect common modes of +/-12V, the leakage current will come into effect during normal operation. If you do not expect your common mode to exceed -7 / +12V than this device should be a good choice. Of course, you should test it in your system to ensure everything works as expected.
    Thanks for asking this question on E2E!
    Best regards,
    Dan