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CDCM7005QFN-EVM: Not locked with some VCO

Yaoting Yang
Intellectual 780 points

Part Number: CDCM7005QFN-EVM

Hi,

In one of our design, we use the circuit shown on page 5-3 of "CDCM7005 (QFN Package) EVM Users Guide". The issue we come up with is for some type of VCO, such as Abracom's ASG-P-V-A-500.00MHz, it can not be locked by cdcm7005. But, it works well for FOX's VCO, such as FVXO-PC73BR-500.00.

Any modification of the circuit parts? Is there any guru can help?

Appreciate a lot!

Yaoting Yang

  • 0
    TI__Mastermind 24205 points

    Hi Yang,

    Can you send us the exact IO configuration desired? Any reason why you are opting for an active loop filter design (5-3) instead of passive loop filter design (5-2)? Given the VCXOs that you are planning to use in your application, it would be good to start with a passive loop filter design.

    You could use the excel based calculator under development tools at the link below to simulate your loop filter design

    http://www.ti.com/product/CDCM7005/toolssoftware

    For the two VCXOs that you mentioned in your email, most specs seem similar. The one main difference was in the Kv (Frequency Change/Tuning Voltage)

    The Abracon VCXO appeared to have a Kv of ~111 kHz / V while the Kv of the FOX VCXO came out to ~72 kHz / V. These parameters can be fed into the spreadsheet during the loop filter calculation.

    Regards

    Arvind Sridhar

  • 0 in reply to Arvind Sridhar
    Intellectual 780 points

    Hi Sridhar,

    Thank you for your response!

    There is no particular reason why we select this active loop filter. Now it is already in our design. We have to figure out why it can not be locked to some VCXO. 

    The following is our configuration to the CDCM7005,

    WORD0 = 32'b0_0_000_000_001001110000_0011111001_00;

    // Word0 setting: 32'h2703e4; M=250(F9H); N=625(270H); all phase delay are "0"s; Manually switch ref_clock;else are default settings.

     

    WORD1 = 32'b0_0_0_0_0_0001_0000_0000_0000_0000_1_1_1_1_1_01;

    //Word1 setting:32'h80007d;  CH0~3 are active LVPECL, CH4 is 3-state;else are default settings.

     


    WORD2 = 32'b1_1_0_1_101_011_011_011_001_011_00_1010_0_1_10;

    //Word2 setting: 32'hdadb2ca6; CP_DIR=negative; PRECP=off; CP_Current=default(Ah); PFD_PulseWidth=default(0h); FB_MUX(P)=4(3h); Y0_MUX=2(1h); Y1_MUX=Y2_MUX=Y3_MUX=4(3h);else are default settings.

     

    WORD3 = 32'b00000000000000000000_0_0_0_00_0_10_01_11;

    //Word3 setting: 32'h27; all are default settings.

     

    The spread sheet for CDCM7005 you give me is only for a passive loop filter. No help for our case. Is there any one for a active one?

    Looking forward to your help! Appreciate!

    Yaoting Yang