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Original question:

LMX2594: OSCin differential drive datasheet suggestion

LMX2594: Using HCMOS oscillators

Keith clark
Prodigy 130 points

Part Number: LMX2594

The previous query asked a question regarding the oscillators used as a clock source for the LMX2594. It was stated that the oscillator should be connected to the upconverter using 50 Ohm terminated transmission lines (to reduce reflections). However, when an HCMOS oscillator was used the 50 Ohm terminations prevented the oscillator from working. Can I assume that, over a short distance, a single ended HCMOS oscillator should be connected to pin 8 of the LMX2594 via a 100nF capacitor whilst pin 9 should be left floating?

Many thanks for your help.

Best regards

Keith

  • 0
    TI__Mastermind 28031 points
    Keith,

    One thing is that the input as seen looking OUT of the OSCin and OSCin# pins should be the same. If you do not do this, you might get high spurs.

    So what I would do on this:
    For OSCin pin, take your oscillator and put a series Res, shunt Res, series Res, then series 100 nF cap.
    For OSCin# pin, take series Res from cap and shunt 100 nF Cap.

    For the first try, maybe take your oscillator and do series 18 ohm, no shunt, series 0 ohm and 100 nF to OSCin.

    Then on other pin, try coming out with series 51 ohm and shunt 100 nF cap.

    Now I think that you should have some flexibility to tinker with this network.

    Regards,
    Dean