Clock generator

Sep 17, 2006 2 Replies
J

Hello,



I am using the cypress clock generator CY2292F to generate a clock of



25Mhz for my CPLD ( ATF1508 AS). The CY2292F has a load impedance of
15pf , if it is programmed as 3.3volts. The cpld has 10pF input impedance. Now, I am having following problems with the part


  1. If I program it for 25Mhz then it produces like 13 Mhz. So I have to program it for 50Mhz to generate 25Mhz.

  2. like an hour after the powerup the cy2292f changed its frequency to

30Mhz and the clock waveform looks like sine wave instead of square wave.

Please advice!



Thanks john



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P

Apart from excessive loading, I would suggest talking to Cypress for tech support. They'll want the programming file and appropriate schematic pages (which would help here too).

I have used the CY229x series myself, (in a high volume product) and I had no problems at all with the part.

Without some real details, it's hard to help.

Cheers

PeteS

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V

How long distance you have from the CY to CPLD and how looks your PCB? (multistrat with ground plane?)

It looks like either the PLL has unlock, either the input oscilator is wrong. Test first the XTALOUT using a 10:1 probe for your scope. BTW, your scope is ok ?

greetings, Vasile

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