what's wrong with my 32.768K clock source?

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liuzhili

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I made a board as this schematic to get 32.768K clock source, but it couldn't generator 32.768K clock freq. I saw more than 60MegaHz at TP25, What's wrong? I don't know how to do to get 32.768KHz clock?
any suggestion? or any other fine schematic that could generate 32.768Khz?
thank you~~~
 

The load capacitance of the 32768kHz crystal is ≈15pF, so you can't have 2 x 1nF caps near it ..

Try the following values:
C124 10pF (or less)
C255 33pF
R188 100kΩ-330kΩ
R190 10MΩ or more ..
Also, I can't see any reason why you have C286 and C287 connected to the output of the U20B .. just remove them ..

Regards,
IanP
 

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