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Connected receiver inputs on SN75C1167

Intellectual 1750 points

Replies: 2

Views: 505

Hello,

I was wondering is there a reason to connect the differential receiver inputs on SN75C1167 (1A and 1B for example) via a small resistance (~100)? If so can you explain why. If not, then please verify that this is not an appropriate connection.

Thank you!

  • Sep,

    The rise and fall time of RS-422 signals is fast enough that the RS-422 cable becomes a transmission line. All transmission lines have a characteristic impedance. The driver see this impedance and the signal power propagates down the cable just fine. At the receiver end of the cable, one of two things can happen. If the receiver has a resistor whose value matches the cable impedance then the power from the cable is absorbed and nothing else happen (except resistor heat). If there is no resistor, the power from the cable has nowhere to go; it will reflect back down the cable back to the driver. Unless specifically designed, the driver won't match the cable impedance so some of the power heads back to the receiver again. All these reflection greatly degrade the signal quality.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Thank you Ronald!

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