Clock generator

[john]

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

 

[PeteS]

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

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

 

[vasile]

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

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

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.

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