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LMX2572: LMX2572

MIGUEL HERNANDEZ BERTO
Prodigy 20 points
Part Number: LMX2572
Other Parts Discussed in Thread: LMK04828, LMX2594

Dear E2E forum staff,

My question is regarding the design option of Phase Synchronization of Multiple PLL Synthesizers based on LMX2572 reference part number.

I want to synchronize (x4) synthesizers (LMX2572 ) and I am wondering to know if it is enough only to use (x1) LMK04828 reference (attached figure)

- OSCout (LMK04828 ) --> REF_IN (LMX2572) 
- SDCLKout_XX (LMK04828 ) --> SYNC (LMX2572)

or otherwise I need a minimum of (x2) LMK04828 devices ?



Could you please send some schematic drawing with the right routing signaling?

Thanks in advance for your support.

  • 0
    TI__Mastermind 28011 points
    Miguel,
    Yes, this is exactly the approach to use. A few things to be aware of:
    1. The SYNC feature of the LMX2572 makes the phase consistent through power up cycles, switching frequencies, ... ect. However, it does not mean that the propogation delay throught the devices is the same. For this delay, you can adjust this out with the MASH_SEED or LMK04828 delays.
    2. If the output frequency of the LMX2572 is a multiple of the input frequency, this is a category 2 phase sync and you have the option of doing this in software, although you can still use the pin.

    REgards,
    Dean
  • 0 in reply to Dean Banerjee
    Prodigy 20 points

    Dear Dean ,

    Thanks a lot for your reply, very useful information.

    In the same way, could you please validate this topology to understand better the concept behind the final solution design. Attached this image in which I try to clarify the concept.

    Thanks in advance for your support.

    BR, Miguel

  • 0 in reply to MIGUEL HERNANDEZ BERTO
    TI__Mastermind 28011 points
    Miguel,

    I understand why you take 4 outputs to the 4 LMX2572, I agree with this.

    However, lets discuss the SYNC pin.

    First realize that the SYNC pin is only necessary of the output frequency of the LMX2594 is not a mulitple of the input. For instance, if you produce 300 MHz from a 100 MHz input signal, although you do need to apply a SYNC pulse, the timing of this pulse is not critical and can even be done in software (Category 2).

    Now suppose the output frequency is NOT a multiple of the input frequency for the LMX2594 (Category 3). In this case, you do need to apply an input signal to the SYNC pin and the timing is critical. However, if you have the LMK04828 available, why don't you just use the SYSREF outputs from that?

    Regards,
    Dean