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SN65HVD11: about SN65HVD11D A/B port shorted current

Vera Mao
Expert 5065 points
Part Number: SN65HVD11

hi dear supporting team,

as for SN65HVD11D, because it is at the brd edge which interface to external, if in lightening stroke,  suppose the A/B prot pin is shorted to GND,  could we gurantee the shorted current to GND be smaller than 50mA over whole temp range? if it is exceed 50mA,  is there any internal protection that could shut it off, and when the shorted case is passed, then it could recovered itself?  tks a lot!

  • 0
    TI__Guru 62920 points
    Hi Vera,

    When there is a short-circuit on the A or B line, the device limits the output current to +/- 250 mA (see the IOS specification in the datasheet). This condition results in high power dissipation within the IC as well, and the heating produced by this is typically enough to trigger the device's internal over-temperature protection circuit, which would then disable the outputs until the device cools off. You may observe the device cycling on and off in this case as the thermal shutdown is reached, device is disabled, device cools off, re-enables outputs, and then heats up again.

    In both cases (output current limited only by IOS protection or outputs shut off due to thermal protection) the device will recover automatically once the short-circuit condition is removed.

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    TI__Expert 5065 points

    hi Max,

    thank you for your answer!

    so double check with you: they have thunder preventer on brd,  when it works, it will cause HVD11D output shorted to GND.  in case that after the thunder, the thunder preventer keep conducting and recover the circuit,  they will request that after the thunder, HVD11 provide smaller than 50mA current..then the circuit will recover.  so since after we provide +/-250mA and then will shut off automatically, then the current to the thunder preventer will be less than 50mA,  then it will stop conducting, and in the mean time, it could also protect SN65HVD11D, right?  tks!

  • 0 in reply to Vera Mao
    TI__Guru 62920 points
    Vera,

    I just noticed that I responded to you previously via email but not through the e2e forum. For the benefit of future forum users, my response is below.

    Best regards,
    Max

    __

    Yes, I would expect it to work this way in most cases. It probably isn’t a good idea to rely solely on thermal shutdown, though, since there may be some cases (e.g., operating at colder ambient temperatures) where the shorting condition does not cause enough heating of the IC to trigger shutdown. It would be better if the <50 mA current condition could be forced either by toggling the DE line (to shut off the driver circuit) or the D line (to drive the opposite state). Most RS-485 applications will do this regularly (it wouldn’t make sense to constantly drive a single logic state), but you could check to make sure that the toggling that occurs during normal operation is enough to reset the thunder preventer – it may have some minimum time for the current to be low enough before it fully resets.