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Crystal design on KEA platform

Question asked by Robert Maier on May 31, 2019
Latest reply on Jun 5, 2019 by Robert Maier

Hello,

 

I am using the S9KEAZN64ACLH. I have an issue where the external clock occasionally fails to start. It is only an intermittent issue. Maybe 1-2% of the time, and is usually more common on certain PCBAs.

 

Attached is the schematic and layout of the crystal used. The crystal has a load capacitance of 20 pF and 16MHz frequency. The load caps are actually 43pF, so the resulting load capacitance here is 21.5pF. R76 has been tried with anything from 0.0 to 6.75k. Lower resistance usually helps, but is not a silver bullet. Replacing C42 and C43 helps, but the only thing that really works is replacing the crystal. So far, that seems to be the only 100% fix.

 

Any ideas on what could be causing this issue? Is it stray capacitance?

 

 

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