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Input circuit of SN65HVS881

Ken Hashi
Intellectual 790 points
Other Parts Discussed in Thread: SN65HVS881

Hello.

My customer evaluates SN65HVS881, and be the questions of the input terminal evaluation.
Ask you a question surely about three main checks of the input circuit which was written to the figure below to understand that I can input a signal.

Q1.What kind of circuit does the Iin>Leakage threshold check go by?
      Do detect the voltage by I/V conversion?

Q2.What kind of signal is the signal which cannot pass Iin>Leakage threshold check?

Q3.How can check on that Iin>Leakage threshold check functions correctly?

Q4.A switch seems to be replaced by the REx side in Input =Valid, but does the current pass to the FGND side break off?

Give my best regards.

k-hashi

  • 0
    TI__Mastermind 20820 points
    Hi k-hashi,

    I do not understand your questions. What leakage current are you talking about? The value of ILIM is set by RLIM and its range is specified in the datasheet.

    Can you please clarify your questions so that I may provide you a better answer?
  • 0 in reply to Michael Peffers
    Intellectual 790 points
    Hello Michael.

    I am sorry that I cannot explain the question that is clear to you.

    Want you to tell "leakage threshold check" of previous figure "Simplified Input Stage" not a question of Leakage current.
    We think that it is a check to be turned on only when Iin is higher than 0.5* Ilim current.
    How will this circuit refer to the threshold?

    My customer wants to understand a circuit to check this function works correctly.
    Or please tell a way to check this function.
    The customer asks for information to be afraid of the malfunction of such a protective circuit very much.

    Please inform the circuit information that you can disclose
    Give my best regards

    k-hashi
  • 0 in reply to Ken Hashi
    TI__Mastermind 20820 points

    Hi K-hashi,

    I apologize for my delay in response on this.

    I think I understand what your customer is asking now. I believe that they are interest in at the threshold levels at which the device will transition from a high to a low or low to a high. Figure 1 from the datasheet gives us a good idea of the limits of this parameter which is based on the RLIM value. As we have seen already RLIM sets the current limit of the part and we can see from this plot how the current consumption changes with the RLIM value. It is clearly seen that the bigger the RLIM resistor the smaller the current consumption will be from the three values tested in this plot.

    RLIM is bounded though and cannot be any arbitrary value. RLIM is bounded to be in between 17k ohms and 500k ohms. Unfortunately I do not have any outside of what is provided in the data sheet but you can imagine that with 500k ohms on the RLIM pin that the current consumption would be less than the a curve in the plot above. I think that we need to add a equation to the datasheet that allows for the current consumption to be calculated given a RLIM resistor value but as of now I do not have that information. I will work internally with my team and the design team to see if this is an ascertainable equation and see about adding it to the data sheet. It may turnout that the relationship is non linear making it difficult to spec (I am not sure about this though)?

    Another thing to note here is that the datasheet guarantees a low with any voltage on the input that is <=4V and a high with any voltage on the input that is >=5.5V. So, regardless of the current consumption this is voltage driven spec. I hope this helps, please let me know if you have more questions?

  • 0 in reply to Michael Peffers
    Intellectual 790 points
    Hi,Michael-san

    Thank you for giving an answer.

    We could understand the good point of this IC, but my customer for fear of a trouble said if there was too little information to understand movement.
    So surely think your suggestion to be useful to a customer.

    If information listed in a data sheet or the information of the application notebook is added, and please tell it.

    Thank you in advance for your help.
    Give my best regards.

    k-hashi.