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CC2564: External clock - recommended 10nF shunt capacitor kills clock source.

Mark Green
Prodigy 80 points
Part Number: CC2564

Hi,

We are using a external 26MHz square wave oscillator.

Section 6.3.2.1 of the datasheet recommends fitting a 10nF shunt capacitor to reject high frequency components.

But 10nF is 0.6ohms at 26MHz, so it kills the clock source too.

Should this be 10pF? or even lower?

Mark.

  • 0
    TI__Intellectual 1930 points

    Hi Mark,

    You can use a lower value according to your DS - 10pF is OK , either way please use a 0.1uF on the supply as well to keep the supply voltage clean. 

    Eric.

  • 0 in reply to Eric Greenstein
    Prodigy 80 points

    Hi Eric,

    Thank you for the quick response. I'll fit 10pF and ensure 100nF is on the supply to the oscillator.

    It seems to me that the suggested value of 10nF in the datahseet would rarely be practical. I can't think of an off the shelf clock oscillators that could drive 26Mhz into 10nF and present a meaninful voltage.

    Shouldn't this either be corrected on the datasheet, or a note added at the very least?

    Mark.