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ADS8588SEVM-PDK: J9 Resistors

Mark Philip Felipe
Genius 10850 points
Part Number: ADS8588SEVM-PDK

Hi Team, we would like to seek clarification on the J9 Resistors. How did we arrived on 49.9?

Thank you

-Mark

  • 0
    TI__Mastermind 45805 points

    Hi Mark,

    Are you asking why 49.9ohm resistors are used instead of other value? thanks.

    Regards,

    Dale

  • 0 in reply to Dale Li
    TI__Genius 10850 points

    Hi Dale, yes I am trying to look into the reference however on my search there are no direct information for this.

    Hoping for your response.

    -Mark

  • 0 in reply to Mark Philip Felipe
    TI__Mastermind 45805 points

    Hi Mark,

    These series termination resistors are used for impedance matching at the source and prevent any possible reflections on the driver end of the trace. A voltage overshot can be significantly reduced by matching the impedance of the driver to the characteristic impedance of the transmission line. The series resistor value is selected according to the driver impedance and the transmission line impedance. Notice that these scale with the signal frequency and the combined sum of the termination resistor and the driver output are equal to the impedance of the trace.

    A simulation is a good way to determine the suitable series resistor value. An appropriate resistor value for series termination should be chosen:

    • If the resistance is too small, the termination may not effectively reduce or eliminate the overshot.
    • If the resistance is too large, the driver may not sufficiently drive the transmission line.

    However, regarding the situation of the EVM board, I do not think you can see a significant difference by using 49.9ohm or 33ohm series resistors.

    I hope this helps.

    Regards,

    Dale