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LMH0346 - Reference Clock

Guru 19775 points
Other Parts Discussed in Thread: SD3GDAEVK, LMH0346

Hi Team,

I have some question about the reference clock.

[Q1]
I am looking at the User Guide of SD3GDAEVK.
LMH0346 schematic uses "ABRACON ABMM-27.000MHZ-B2-T" crystal.

Do you have any other proven crystal information ?

* I am understanding the required specification, Datasheet p.13 "Table 3"

[Q2]
When using XO for Reference Clock, I believe XO CMOS 27MHz clock should be input to XTAL IN / EXT CLK pin.
Can you just leave XTAL OUT pin OPEN ?

Best Regards,
Kawai

  • Hi Takushi San,

    We are looking into this case. Someone will provide a reply soon.

    Regards,

    TK

  • Hi Takushi-San,

     

    1)      In the time since we released the SD3GDA evaluation kit, we have tested a new 27MHz crystal for our SDI Reclockers. We recommend using p/n 1B427000ZZ0A by KDS. The KDS crystal has specifications comparable to the Abracon, but with a lower drive level. In addition, the C17 and C18 capacitors in the SD3GDA schematic should be replaced by 15 pF caps with a comparable voltage rating. 

    2)      You are correct that you can apply a 27MHz LVCMOS external reference clock to the ‘XTAL IN/EXT CLK’ pin. In this case, the ‘XTAL OUT’ pin should be left floating. However, we recommend AC coupling and biasing the crystal input pin as well when using an external clock. The external clock should be applied to the C6 AC coupling cap in the example shown below.  The 1kΩ terminations in combination with the AC coupling cap are sufficient to constrain the common mode voltage at the input of the reclocker so that stable operation is maintained.

    Thanks,

    Kevin Ginunas

  • Hi Kevin-san,

    Thank you for your reply.

    Please let me confirm about the crystal resonator.

    1) I could not find the crystal resonator which part number is "1B427000ZZ0A".
    Is this DSX321LS family device ? Please let me confirm if 1B427000ZZ0A is this device in the following URL.

    https://www.kds.info/data/pdf/013E.pdf


    2) I understood. Thanks for giving us the information of the recommended schematic.

    Best Regards,
    Kawai

  • Hi Takushi-San,

    Yes DSX321SL is the correct part number from KDS.

    Thanks,

    Kevin

  • Hi Kevin-san,

    Now I'm clear !

    Thanks for your prompt reply.

    Best Regards,
    Kawai

  • Hi Kevin-san,

    Could I ask you about the load capacitance for KDS crystal, DSX321SL ?

    https://www.kds.info/data/pdf/013E.pdf

    You could choose load capacitance from several value, such as 8pF, 10pF, 12pF,,,,.

    When using the recommended 15pF capacitor for C17/C18 in SD3GDAEVK, which load capacitance should you choose for DSX321SL crystal resonator ?

    Best Regards,
    Kawai

  • Hi Takushi-san,

    The testing that KDS ran using our SD3GDAEVK was conducted using a 18pF loading cap. That is the load capacitance we would recommend.

    Thanks,

    Kevin

  • Hi Kevin-san,

    Thanks for the information.

    Best Regards,
    Kawai