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LMK04828BEVM: Internal VCO

Hector Andres Gomez Alvarez
Prodigy 30 points
Part Number: LMK04828BEVM
Other Parts Discussed in Thread: LMK04828

It's possible to replace VCO with another crystal oscillator? I want to generate a 120 MHz frequency without use any VCXO, but I don´t know if the internal VCO is enough to generate it.

  • 0
    TI__Expert 8865 points

    Hello Andres

    Can you let us know a bit more on your requirements for input and output clocks? Do you want to use the device in the dual loop jitter cleaner or single PLL mode? Normally it is possible to generate the 120MHz output with the internal VCO witout using a VCXO and using PLL2 only mode.

    Best regards

    Puneet

  • 0 in reply to Puneet Sareen
    Prodigy 30 points
    Hello Puneet,

    I want to work with the device in the dual loop jitter cleaner,
    I would like to work with two types of output clocks, the first one (f1) at 120MHz (or maybe at 10 Mhz), and the second at f1/10.
    I want to work with the internal VCO.
  • 0 in reply to Hector Andres Gomez Alvarez
    TI__Expert 8865 points
    Hello Andres,

    For dual loop jitter cleaner, one VCXO is needed. PLL1 works only with the external VCXO, there is no internal VCO for PLL1. Can you please let us know the input clock frequency, jitter/phase noise performance needed at the output clocks, phase noise of the input clock?

    Best regards
    Puneet
  • 0 in reply to Puneet Sareen
    Prodigy 30 points
    Hi,

    I would like to work with one clock (f1) tunneable between 10 MHz and 120 MHz, and with other f2=f1/10.

    Do you have and schematic for VCXO connection?

    Do you know a VCXO model to work for?
  • 0 in reply to Hector Andres Gomez Alvarez
    TI__Expert 8865 points
    Hi Andres,

    Based on your input frequency, you will have to select the appropriate VCXO. the VCO of the PLL2 can be run at 3GHz and dividing it down will give you 10MHz & 120MHz. You cannot have any frequency between 10MHz to 120MHz as the LMK04828 is an integer PLL device.
    For the VCXO connections, you can refer to this document:
    www.ti.com/.../snau145
    VCXO model can be written in verilogA, i can help you with that.

    I am not sure if LMK04828 is the right device you are looking for. If you give me more information about the use case input/output frequencies, i may propose you the right device.

    Best regards
    Puneet