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AD9522-1 internal VCO problem

Question asked by dmv on Mar 16, 2015
Latest reply on Apr 2, 2015 by pkern

Hi,

 

I designed a PCB that includes an AD9522-1 that I intend to use for clock distribution. The supporting circuitry for the AD9522-1 is basically a copy of the AD9522/PCBZ Evaluation Board (which I also use to program the AD9522-1 in my design by means of the AD9522 Evaluation Software).

 

I program the AD9522-1 in order to output several clks of 200 MHz locked to a 10 MHz input signal. I use the following configuration:

 

  • Operational Mode: Internal VCO and CLK Distribution
  • PLL Mode: Norm Op
  • REF1: 10 MHz input
  • R Divider =1
  • N Divider=240
  • VCO Divider=2
  • Channel Divider=6

 

This configuration works fine when using the Eval Board. However, I am unable to get an clk output when using my design. At the most, I get a high level signal when I program an output channel in CMOS format. Using the STATUS pin, I have verified the following:

 

  1. The R Divider Output is correct.
  2. The N Divider Output is always low.

 

Even though the absolute absence of an output signal suggests me that it is not a problem of the external loop nor the charge pump current, I have tried changing these parameters with no success. As for a chip or soldering failure, I get the same results in three different PCBs.

 

My feeling is that I am missing something quite basic, any suggestions?

 

Thank you very much.

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