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CDCEL913: CDCEL913 clock configuration

Kazuki Kuramochi
Expert 8330 points
Part Number: CDCEL913

Hello Expert,

I have questions regarding CDCEL913 as following.
Would you answer it?

  1. Datasheet said recommended crystal input freq ranege is up to 32MHz. But there isn't freq range regarding VCXO. Does it mean I can use higher frequency VCXO (e.g. 72MHz) for this device?
  2.  I'd like to generate clock as Y1=72MHz, Y2=12MHz from the 72MHz input. At this time, Is Y1 and Y2 phase synchronized?
  3. Is there any way of configuring output as 12MHz from 72MHz with out configuring I2C?


I'm looking forward to hearing back from you.


Thank you and best regards,
Kazuki Kuramochi

  • 0
    TI__Expert 8585 points

    Hello Kazuki,

    1. The VCXO has the same frequency range as the crystal (8 MHz to 32 MHz).

    2. First, if you want to provide a 72 MHz input, make sure that the LVCMOS input mode is selected. Second, Y1 and Y2 will not be phase synchronized because the output division to make Y2 = 12 MHz changes the phase from that of Y1 = 72 MHz. 

    3. No, you must configure the I2C to have an output of 12 MHz. The default divider values are all 1 and must be changed to 6 configure the output frequency to 12 MHz.

    Regards,

    Kia Rahbar

  • 0 in reply to Kia Rahbar
    TI__Expert 8330 points

    Hello Kia,

    Thank you for your explanation.

    I have question for your answer.
    Your answer for question 1 is this device's recommended input clock range is 32MHz regardless of clock source.
    But answer for question 2 seems this device support 72MHz.
    Could you guarantee the normal operation with 72MHz clock source?

    Thank you and best regards,
    Kazuki Kuramochi

  • 0 in reply to Kazuki Kuramochi
    TI__Expert 8585 points

    Hello Kazuki,

    If the input is in the VCXO configuration, then the frequency can go up to 32 MHz. The VCXO frequency is dependent on the crystal frequency.

    If the input is in the LVCMOS configuration, then the frequency can go up to 160 MHz.

    Therefore, a 72 MHz input is possible if the LVCMOS configuration is used for the input.

    Regards,

    Kia Rahbar

  • 0 in reply to Kia Rahbar
    TI__Expert 8330 points

    Hello Kia,

    Thank you for your kindly explanation.

    I understood we must use this device with "LVCMOS" 72MHz clock source for achieving required output.


    Thank you and best regards,
    Kazuki Kuramochi