AnsweredAssumed Answered

ADV7612 Crystal Problems

Question asked by gatorgreg on Aug 27, 2012
Latest reply on Jan 6, 2014 by GuenterL

Hi,

 

I was wondering if you might know of why I am experiencing problems with the 28.6363 MHz crystal?  I have a board design whereby three different crystal parts were used (all of them 28.63 MHz parts). 

 

On one of the parts (made by NDK), the crystal runs at 9.5MHz not matter what I do to the shun cap values.  Even using the ADI cap formula yeilds no solid results.  The shunt caps are currently 10pF with a 390k resistor across the crystal.

 

On the other two crystals (both made by Rami), one part has a Cload of 20 pF and it has not failed to date - the crystal runs at 28.6MHz as soon as power is applied.  The other part (which has a Cload of 30pF) runs at 9.5 MHz as well. (this occured on one board and other boards with this same crystal seem to work).  Even moving the Cshunt to 47 pF (base on the 7612's cap value formula) did not make a difference.

 

Is there anything you can tell me about the 7612's crystal drive strenght or any other insight as to what could be causing this kind of behaviour?

 

Thanks,

Greg

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