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THVD1450: Disable Failsafe?

Fatima Elfasi
Prodigy 60 points
Part Number: THVD1450


Tool/software:

Hi transceivers team,

My customer is using the THVD1450DR and wanted to know if there is a way to disable the failsafe feature (which is typically active high, to my understanding). The idle is particularly unwanted on his end.

Would adding resistors disable this, or is there something he can do to achieve this?

Thank you and I look forward to a response. Let me know if you need additional info from me or the customer.

Best,

-Fatima

  • 0
    TI__Prodigy 430 points

    Hello Fatima,

    This internal failsafe will bring only the input receiver to go high when it is either disconnected from the bus, shorted, or when it is not currently being driven. If your customer would not like this, you can force a differential signal of more negative than -200 mV by using a pullup and pulldown resistor. Unfortunately, this does not "disable it", you are just preventing it from idling at 0V. Is there a specific reason it is unwanted on his end?

    Best, 
    Leah Jones

  • 0 in reply to Leah Jones
    TI__Prodigy 60 points

    Thanks for your response. I received this as a follow-up from the customer, which may help us understand why he does not want the active high.


    "I sincerely appreciate the help.  As the failsafe typically goes asserts an active high and is built into most parts these days, the easiest thing for us to do is to put a simple inverter on the input and output of each end.  This will help prevent the transceiver from producing an unwanted active high output.  The part is not being used in a traditional way which is why the failsafe has been problematic, and it is instead simply turning a device on at the end of a line.  You can see why the failsafe would be problematic. 

    If you see a problem with this approach, please let me know.  I appreciate the help."

    Please let me know if you need any additional details from me or the customer. Thank you!

    -Fatima

  • 0 in reply to Fatima Elfasi
    TI__Prodigy 430 points

    Hello, 
    If idling is what he's worried about from the failsafe, then I would recommend my previous suggestion of using a pullup and pulldown resistor, or the inverter he suggested. If there are many devices on the bus though, I would recommend sticking with the inverter due to the loading, but if not, I would recommend the latter.

    I do want to stress the importance of fail safe. You need fail safe in order to get an accurate value of R, and without it, your value will not be correct. I'm not clear on the way it is being used and the specific reasoning, but he can look at our devices with a timer based fail safe (if offset is an issue) or our older sn65hvd devices that do not have failsafe implemented. 

    I hope this clears things up and let me know if you have any more questions. 

    Best, 
    Leah Jones