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Change the VCXO in EVAL-HMC7044 board

A VCXO at 122.88MHz is mounted in EVAL-HMC7044 board, so the inputs to the PLL1 must be divisors of this frequency. My input has to be a signal at 10MHz so I would like to have another frequency in the VCXO, for example 100MHz.

Is it possible to connect an external VCXO through the CPOUT1 output and the OSCIN input? Or can I change the VCXO to another at 100MHz?

Thanks in advance.

Best Regards,

Jose A. Torre.

  • Both is possible.

    • The on-board VCXO can be changed with 100MHz version.
    • The on-board VCXO can be disabled (insert JP2 -not included in the kit) and an external VCXO can be connected to OSCIN_N. It is even better to remove R227.

    Alternatively 122.88MHz VCXO can be locked to 10MHz reference signal without any problem. Use the following parameters:

    R0 prescaler = 5 (fLOS= 2MHz)
    R1 divider = 25 (fPFD=80kHz)
    VCXO prescaler = 60 (fLOS= 2.048MHz – fair close)
    N1 divider = 1536 (fPFD=80kHz)
    CP current = 8 (lower values may cause not locking)

    Note that, the frequencies from both branches to LOS section should be close (equal is not required).