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ADV7611 frequency overshoot on LLC output

Question asked by rlf.mg on May 16, 2014
Latest reply on Sep 8, 2014 by rlf.mg

Hi,

 

I have been looking at EVAL-ADV7611EBZ with DVI input and DVI output and found this problem.

 

Either when switching the source video format or when turning on the video source there appear a small number of clock periods at the LLC output, which are equivalent to frequencies much higher than the specified 165MHz.

 

Using a less-than-width trigger I have found clock periods as high as approximately 208MHz.

There appears to be a dependance on the video format what frequency occurs. Most tests were run skipping from 1680x1050/60Hz CVT to 1920x1200/60Hz CVT-RB.

 

I did check that this is not simply crossing over from the TMDS clock input.

 

The problem with this is the device to be run from the outputs of ADV7611. This device is only specified to somewhat above 165MHz but certainly not up to 208MHz (or maybe even higher). As a result I cannot guarantee a known and working state in this device.

 

Is this known behaviour?

Is there a way to avoid this?

 

Thanks,

rlf

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