• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 34 subscribers
  • Views 1242 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.

TCAN1044AV-Q1: Will this transceiver survive a short to 52V DC on its CAN bus pins?

Richard Webb
Prodigy 136 points

Part Number: TCAN1044AV-Q1

For the above transceiver, will it survive a short to battery (STB) fault of 52V DC indefinitely?

When does the receiver common mode voltage of +-12V need to be considered when adding protection for the CAN bus pins?

Also, to extend the ESD protection to 30kV I intend to use an additional ESD TVS diode between the CAN bus pins and GND, with a Vclamp rating of > 52V (56-76V) so that it doesn't clamp when a 52V STB fault is applied. Any concerns about this or things I need to consider?

Regards,

Richard.

  • 0
    TI__Guru 74972 points

    Richard,

    The CAN bus pins are rated to survive +/-58V relative to GND on each pin. The common-mode range of +/-12V is referring to the voltage range where CAN communication will be correctly interpreted by the receiver. Now, if a short to battery condition happens while CAN communication is occurring and there's a common-mode choke on the CAN bus, there is a chance that the voltage could rise to higher than the absolute maximum due to inductive kickback, and we've seen that cause damage in other applications.

    But to answer your question, yes, 52V DC on the CAN bus will not damage the device.

    Your TVS diode choice will be okay, but again, if the voltage does rise above 58V and the diode doesn't clamp, there will be a chance of damaging the CAN bus pins.

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    Prodigy 136 points

    Hi Eric,

    Thanks for the clarification.

    In the situation where inductive kickback from the CMC should occur during a STB fault, would the ESD protection not clamp this voltage or would I require another protection method? If so, what would you recommend?

    In our application the 52V DC is our battery input voltage from an on car DC-DC and this STB fault would only occur during a crash condition or harness fault during the race.

    Thanks and regards,

    Richard.

  • 0 in reply to Richard Webb
    TI__Guru 74972 points

    Richard,

    Richard Webb said:
    In the situation where inductive kickback from the CMC should occur during a STB fault, would the ESD protection not clamp this voltage or would I require another protection method? If so, what would you recommend?

    Typically, yes, it would, but it depends on the length of time the inductive kickback occurs, and the rise time of said waveform. ESD protection integrated into the device is meant to respond to a very fast rising edge, and then shunt the current driven into the bus pins to GND for a short period of time, in the nanoseconds. If this voltage persists for longer, a TVS diode may save the device. That being said, if this occurred during either of the faults you mentioned, I'm not sure it would matter if the CAN transceiver was damaged because there are larger problems to manage.

    I have seen many cases where the inductive kickback from the CMC was so short that it really had no effect even when the voltage rose to 10V higher than the absolute maximum. If the two situations occur, would CAN communication still be happening? That's the crux of this, if CAN communication is occurring during the short or not.

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    Prodigy 136 points

    Hi Eric,

    On the race car, cameras will be running and so they can capture what happens from the camera feeds and sensors all over the car, before, during and after the crash event!

    It depends on what units are talking over CAN during this unfortunately event, but I just don't know that much detail.

    I suppose we could simulate what sort of kickback we may get from the CMC when applying a 52V short, so I'll go down that route next.

    Thanks,

    Richard.

  • 0 in reply to Richard Webb
    TI__Guru 74972 points

    Richard,

    Understood on the application, and sounds good on the test. Please let us know if you have any other questions after testing.

    Regards,

    Eric Hackett