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AM26LS32A: differential impedance on layout

Part Number: AM26LS32A

Hi Sirs,

Sorry to bother you.

As title, we have question on LS32A layout differential impedance.

If input is Differential Line, does input differential impedance is 100 ohm and output is 50 ohm??

If output is Differential Line, does output differential impedance is 100 ohm and or input is 50 ohm??

Or have others suggestion?

Thanks for your reply.

  • Hello Shu-Cheng,

    I don't think I totally understand your question, so if I am mis-interpreting please let me know. For RS-422, the cabling typically has a differential-mode characteristic impedance between 80 Ohms and 120 Ohms. This means that the differential PCB traces (for both inputs and outputs) should be laid out to have a similar characteristic impedance. The termination resistor at the furthest receiver should also have a resistance that matches this value. The impedance on the single-ended logic lines (G/Y/etc.) is not critical.

    Here is an app note that may be useful to your understanding of how to implement an RS-422 or RS-485 link:

    www.ti.com/.../slla070d.pdf

    Max