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SN65HVD21M-EP: Pin Failure

Jackson Chard
Prodigy 20 points
Part Number: SN65HVD21M-EP

We had a high voltage transient above 30 volts on both output pins in the driver mode. After an unknown number of these transients, one of the output pins (pin 7 on the B line) no longer output the correct voltage, and is unable to be decoded. We are looking for some info on failure modes and such that you have seen, and possible ways to mitigate or remedy this failure.

  • 0
    TI__Mastermind 25705 points

    Jackson,

    This device has the +/-27V abs max at output pins. Any voltage exceeding the range would potentially damage the device. However the failure is a statistical figure. With longer duration and higher voltage, it's easier the device fails. Do you put termination on the bus? Do you have the characterization of the 30V transient? If so, you can consider adding small series resistor to limit the current therefore reduce the peak voltage at the pins.

    Regards,

    Hao

  • 0 in reply to Hao L
    Prodigy 20 points

    Thank you for the helpful info Hao! I did have one more question... the failure mode we are seeing is a pin unable to output the correct voltage and can't be decoded. Here is a graph. 

    I was wondering if you could comment on this failure mode... have you ever seen/mitigated something like this?

    Thank you,

    Jackson

  • 0 in reply to Jackson Chard
    TI__Mastermind 25705 points

    Jackson,

    I've never seen this kind of failure on this device but have seen the similar behavior on some other RS485 (BTW, the graph doesn't show correctly). Like I mentioned, adding small resistors is a common solution.

    Regards,

    Hao