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LMK04832: Output frequency

alen
Prodigy 80 points
Part Number: LMK04832
Other Parts Discussed in Thread: LMK04616, LMK04610

hello 

  The frequency range of VCO0 and VCO1, as shown in the datasheet, with output divider values up to 1023 for clk output,  Seem that I cannot obtain frequencies lower than 3M？ How can I get a frequency of 2M, I also need 200M and 100M at the same time.

  • 0
    TI__Mastermind 30040 points

    Your options with LMK04832 are limited:

    • Use an external VCO or VCXO at a lower frequency
    • Use an external divider for the 2MHz signal
    • Use an external clock source at a lower frequency and operate LMK04832 in distribution mode

    Other devices such as the LMK04610 or LMK04616 have a wider divider range, and they might be a better fit for this application.

  • 0 in reply to Derek Payne
    Prodigy 80 points

    Thank you for your reply. If I use the internal integrated VCO of LMK04832, I cannot obtain 2M. However, if I don't use VCO, only use the LMK04832 as a divider, with an OSC IN input of 200M, I can obtain output frequencies of 2M, 200M, and 100M. If I do this, do I need to adjust the circuit design ?

  • +1 in reply to alen
    TI__Mastermind 30040 points

    In the divider-only distribution mode use case, you must ensure the 200MHz input source is delivered to CLKin1 (which has direct access to the clock distribution path). The remaining configuration changes can typically be handled purely in register settings on the LMK04832. The only other exception is if you depended on OSCout at startup to deliver register programming (e.g. if OSCout is the housekeeping clock to an FPGA that initially configures the LMK04832). If you were relying on OSCin -> OSCout buffering as a startup clock, this would no longer be possible: the distribution clock must go into CLKin1, there is no route to the clock distribution path through OSCin, and no outputs are active until after programming except OSCin -> OSCout buffering. You would need a buffer on the reference input or an alternate clock source on startup to replace the OSCout clock if used.

  • 0 in reply to Derek Payne
    Prodigy 80 points

    Thank you, it seems using an external VCO is a better option