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SN75C1167 - Treatment of Unused Input/Output pins

Guru 19775 points

Replies: 3

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Hi Team,

Could you please tell us what to do with the unused Driver/Reciver pins ?

  Driver : 2D, 2Y, 2Z
  Receiver : 2R, 2A, 2B

 The answer for receiver was in the following URL.
http://e2e.ti.com/support/interface/industrial_interface/f/142/p/102795/361353.aspx#361353

I am understanding that receiver differential input, 2A : Pull up, 2B : Pull down (or the opposite).
Is pull up or pull down resistor needed to these pins ?
If you have a recommendation, please tell us the recommended resistor value.

For the driver input 2D, I think it should be pulled up or down. Outputs could be left open.

Best Regards,
Kawai

  • Hi Kawai,

    I agree with the answer you found for what to do with the receiver pins. For the driver pins I would recommend tying the input 2D either high or low. It is never recommended to float a CMOS input as it can float and cause the device to draw large amounts of current.

    I checked the data sheet and it does not look like it will make much of a difference (from a power standpoint) if you tie the 2D pin high or low, just make sure that one or the other is chosen. The two output pins of the driver (2Y and 2Z) can be left floating.

    There is an app note below that decribes what can happen when floating input pins below for reference. 

    http://www.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=scba004c&fileType=pdf

    Please let me know if you have any other questions.

    Thanks,

    John

  • Guru 19775 points

    In reply to John Griffith:

    Hi John-san,

    Thank you for your reply.

    How about the resistor for the pull up or pull down ? How about 10k for each pull up or down ?

    *For the receiver input, it seems that the pins have fail-safe circuit(weak pull up/down). But if the device is used in noisy environment, I think maybe a 10k would be better.

    What do you think ?

    Best Regards,
    Kawai

  • In reply to Kawai:

    Hi Kawai,

    A 10kΩ resistor will work just fine for both the receiver differential inputs (one up one down) and the driver input.

    Thanks,

    John

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