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Altera_Forum's avatar
Altera_Forum
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14 years ago

Slow slew rate option versus ballast resistors ?

Typically in the past I have used 22 ohm source resistors to damp ringing on long trace or cable lengths. I was just wondering if the slow slew rate option is a substitute for the 22 ohm ballast resistors or maybe the combination of both of them may even be better. Of course if I could dispense with the source resistors it would simplify the PCB design somewhat.

My application is to drive an LCD/Display driver using ribbon cable that maybe over 6 inches from the source.

regards

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Series resistors are always good. For signal integrity, emissions, etc.

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    If you have access to an IBIS simulator you can simulate the output with different slew rate configurations and see what kind of ringing you get. If you have a ready made PCB with series resistors and the same ribbon cable you can also replace the resistors with 0 ohm shunts and experiment yourself.

    It is difficult to give a general answer, as it can vary from case to case, but I generally find that keeping some series resistors is more flexible.