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ISO1430: Failsafe function

Michiaki Tanii
Expert 4340 points
Part Number: ISO1430
Other Parts Discussed in Thread: THVD1450

Hello team,

 

Here is the questions from our customer.

 

  1. ISO1430 has failsafe function.
    The failsafe function is only for receiver and it couldn’t contribute to the receiver of other device they use SN75176.
    Is it correct ?
  2. In case that DE of ISO1430 is L or unknown, the driver output should be Hi-Z so the bus will be idle if driver of SN75176 is Hi-Z as well.

 

  1. Or Does ISO1430 have the function to prevent the bus idle even if the other driver or ISO1430 output is Hi-Z sate ?

 

<Background>

  • Our customer has two equipment and one is implemented ISO1430 and the other is SN75176.
  • They are considering replace SN75176 to SN65HVD178 to prevent the fail communication during bus idle.
  • In their understanding, question 1 and 2 is yes but question 3 is no but they would like to double check.

 

Thank you and best regards,

Michiaki

  • 0
    TI__Intellectual 1960 points

    Hi Michiaki:

    Thanks for posting your question on E2E.

    Below are my responses to your questions.

    1. Correct, ISO1430 receiver failsafe operation will not affect SN75176 receiver. ISO1430 failsafe functionality is implemented by offsetting the receiver input voltage thresholds. Please refer to Section 10.3.2 of the ISO1430 datasheet for additional details.
    2. Yes, when both ISO1430 and SN75176 drivers are disabled, the A and B bus voltages will be undetermined. Since the RS-485 bus is in an indeterministic state, the R outputs will be indeterministic as well.
    3. You may implement external failsafe biasing resistors to define the A/B voltage during this HI-Z condition. Please refer to this application note for additional details. Alternatively, you may consider our latest THVD1450 to replace SN75176.

    Regards,

    Dushmantha