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CDCM6208 single-end clock input

user3460508
Prodigy 110 points

Other Parts Discussed in Thread: CDCM6208

Hi, 

I want to use 2 16MHz single-ended signals as CDCM6208's input clocks, so I connect them to PRI_REFP/SEC_REFP and connect PRI_REFN to GND via 1k ohm resister, connect SEC_REFN to GND via 1k ohm resister.

the register 4 is set to 0x20b7.

but I found the LOS_REF is 1 which indicates "Loss of reference input observed at input Smart MUX output in observation window for PLL".

Anything wrong among my design?


 

  • 0
    TI__Mastermind 24205 points

    Hi,

    Please ensure that you follow the guidelines in the schematics (Page 78 of the datasheet and as shown below) for DC coupled 3.3V LVCMOS signals on the primary and secondary inputs.

     

    Regards

    Arvind Sridhar

     

  • 0 in reply to Arvind Sridhar
    Prodigy 110 points

    HI Arvind,

    Thanks for your comments.

    I compare my schematic and reference design and found my design is use 1 k ohm resister on C_PRI_N's position, and "VDD_PRI_REF" is 2.5v. other parts are the same. so today I replace this 1k ohm resister with 0 ohm. but problem is still there.

    I have checked the signal input to PRI_REFP and make sure it can satisfy your single-end signal requirement. also even CDCM6208 report such "LOS_REF" alarm, it still can work.

    could you illustrate how this "LOS_REF" works?

    BTW, if you need my schematic, Please let me know your company mail address. I can send it to you.

    Thanks!

    Johson

  • 0 in reply to user3460508
    TI__Mastermind 24205 points

    Hi Johson,

    Please remove the 0 ohm resistors on the C_PRI_N and CLKIN_SECN side and let these pins float. Let me know if that works.

    If you are still unable to make it work, please send me the schematic for review.

    Regards

    Arvind Sridhar