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using CDCM7005 for sceintific controlled clock

ACQUASANTA ANTONIO
Prodigy 40 points
Other Parts Discussed in Thread: CDCM7005

Hi friend

I have few problem at using CDCM7005 because I haven't great experience in PLL e similar

My customer had choose CDCM7005 for a design a scientific  RTC clock

because a RTC must to  work in every situation a source start is a high precsion couple of  cesium clock at 10Mhz

Idea is that when one of this failure system will be change at second cesium source ( without any glitch and with a maximum accepted delay of  1/2 cycle

So I thisnk that is possible to use this two source for syncro a VCXO using CDCM7005 ;

Just only for test I 'm in using a kit of CDCM7005 with a 491,52 Mhz  with output divide for 16

I'm try to program a N register with 1020 ( and MUX choose divide for 16) and M reg with a value 332 ( with a 10Mhz put in primary ref)

for to have a same freq in PFD

But i don't see a output on Y0A syncronized with my primary source

Can you help me ? probabily for no much expereince I don't understund well

 

  • 0
    TI__Expert 4150 points
    I am not sure about your setup. If you use a 491.52MHz VCXO and divide it by 16, you expect the output frequency ot be 30.72MHz, not 10MHz. Therefore, you can not see if the VCXO is locked or not.
     
    I think you need to set your M/N divders such that you divide the 491.52MHz with 6144 and 10MHz with 125 to run the PFD frequency at 80kHz.
     
    Hope this helps, best regards, Fritz

  • 0 in reply to Fritz
    Prodigy 40 points

    Fritz said:
    I am not sure about your setup. If you use a 491.52MHz VCXO and divide it by 16, you expect the output frequency ot be 30.72MHz, not 10MHz. Therefore, you can not see if the VCXO is locked or not.
     
    I think you need to set your M/N divders such that you divide the 491.52MHz with 6144 and 10MHz with 125 to run the PFD frequency at 80kHz.
     
    Hope this helps, best regards, Fritz

    Fritz

    thanks a lot for your feedabck

    I tried with 6144 and 125 but don't  results are the same ;

    Output on Y0A is 30,72Mhz ( that is OK because I choosed divide for 16 ; for try to syncronize I had choose divide for 16 in FB MUX, and 384 in N divisor;

    125 in M divisor ;

    At this point I'm aspect that with my oscilloscope I can see output on Y0A ( 30,72Mhz ) syncronized with my 10Mhz That is a reference

    isn't right?

    In general I understund that I can use any frequenct for reference ; most important that value in PFD for primary and refernce freq are the same

    In this mode VCXO freq is syncronized with refernce freq

    My be I don't understund well and I thanke you very much for your kind and explain

    let me any and I try