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Original question:

SN65HVD11: about SN65HVD11D A/B port shorted current

SN65HVD11: open circuit protection

Aaron Spaete
Expert 4310 points
Part Number: SN65HVD11

Team, 

One of my customers has the following question:

We currently have the device in question in a receiver configuration and I was trying to understand the Open-Circuit protection. Do both inputs (A&B) need to be OPEN for this protection to take effect or can either input being OPEN?

If the device is configured in the transmit configuration and the R pin is being used to monitor the output status, does the R line need a pull up or can it be left unbiased?

Regards,

Aaron

  • 0
    TI__Guru 62910 points

    Hi Aaron,

    Yes, generally both inputs would need to be open.  The failsafe functionality is achieved by making the switching threshold for determining whether the input is high/positive or low/negative slightly negative (rather than centered exactly at 0 V differential).  This makes it so conditions that result in a differential input level near 0 V (such as a short-circuit between A and B, a loss of input signal, or an idle bus without external biasing) get reported as "high" signals.  If you just had one input open and the other toggling with normal amplitude you would still likely have a large enough differential between A and B to detect high and low states.  (You may want to reference this recent thread for additional explanation: https://e2e.ti.com/support/interface/f/138/p/875126/3237902).

    The R output, when enabled by tying /RE low, uses a push-pull output structure that does not require an external pull-up to function.  However, if the receiver is disabled (/RE high) the output will become high-Z.  In this case a pull-up would be useful to make sure that the corresponding MCU input is biased to a valid logic level.

    Please let me know if this is not clear or if you have any further questions.

    Regards,
    Max