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SN75LBC179A - cable / loading

David Tiefenbrunn
Intellectual 785 points
Other Parts Discussed in Thread: SN75LBC179A

Hi,

 

I'm working with the  SN75LBC179A differential driver and receiver.

 

On the balanced driver side, should there be any build out resistors? 

 

On the balanced receiver side, any termination?

 

The system is using CAT 5 data cable, but not a standard data format.

 

Frequency under 2MHz.

  • 0
    TI__Mastermind 28265 points

    If you are using the device in full-duplex mode you need to install 100 ohms termination resistors at each receiving end.

    If you are configurening it for half-duplex communication by connecting the A/B with the Y/Z terminals you need 100 ohms at the two bus ends.

    100 ohms because the characteristic impedance of CAT5 is 100 ohms +/- 15%.

    Also don't forget terminating the unused cable with 100 ohms. Otherwise the non-used cables will operate as antennas, bulding standing waves and stray all kind of noise into your data link.

    Regards, Thomas

     

     

  • 0 in reply to Thomas Kugelstadt
    Intellectual 785 points

    I am using 2 pairs in the cable, one for each data direction.  So I am using full duplex.  The data is continuous in each direction.

    One pair is used for power.

    I will add terminators to the 4th pair.

     

    Thank you,

    Dave