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LMX2594: Some questions about Category for SYNC mode

shen jie
Intellectual 265 points
Part Number: LMX2594
Other Parts Discussed in Thread: LMK00304, LMX2572EVM

Hi，

As the datasheet don't describe clearly, I have three questions about  Category for SYNC mode and MASH_SEED function as below figure shown:

1. What difference is between the two Category1 marked red and blue circle?

2. In the Category1 marked red circle,

Is "SYNC Mode Required" meaning that VCO_PHASE_SYNC must be set as 1?

Is "No Software/Pin SYNC Pulse required" meaning that not need SYNC input and not need toggling VCO_PHASE_SYNC bit? " If yes,  how to trig SYNC action?

3. As I know, the part of Channel divider is included as the IncludeDivider when SYNC Mode is enable. IncludeDivider will be in the loop, and has deterministic delay.

so the CHDIV in the judgment box as below figure shown is the rest of Channel divider which exclude the IncludeDivider part, right?

4. when MASH_ORDER is 0 that means it work as integer mode, Phase Adjust function by programming MASH_SEED value could be work?

Best regards!

Jason

  • 0
    TI__Guru** 108630 points

    Hi Jason,

    "Red" Cat.1 sync requires keeping VCO_PHASE_SYNC = 1 all the time, not toggling. 

    CHDIV is equal to the total divider after VCO. For example, CHDIV = 96 if RFout = 100MHz while VCO = 9600MHz.

    Phase adjustment with MASH_SEED works in both integer and fractional channels.

  • 0 in reply to Noel Fung
    Intellectual 265 points

    Hi, Noel:

    Could phase adjustment  function with MASH_SEED only shift RFoutA or RFoutB? I mean not both at the same time

    For example, as below figure shown：

    There are ~40ps skew between RFOUTA of these two LMX2594 which is brought by in-part skew of LMK00304 . So, I just want to shift RFOUTA for aligning phase of the RFOUTA  of these two LMX2594. I don't shift SYSREF output on RFOUTB, because two LMX2594 is synchronized by external SYNC signal.  

    Thanks in advance!

    Best regards!

    Jason

  • 0 in reply to shen jie
    TI__Guru** 108630 points

    Hi Jason,

    SYSREF has independent delay control, you  can use MASH_SEED to align the phases of RFoutA and use sysref delay control to align the phases of sysref clock.

  • 0 in reply to Noel Fung
    Intellectual 265 points

    Hi，Noel:

    Could you please provide me some programming demonstration for MASH_SEED ?  Datasheet almost don't describe some specific details. 

    For example, as below figure shown, I want to shift RFoutA about 25ps. 

    .

    Thanks in advance!

    Best regards

    Jason

  • 0 in reply to shen jie
    TI__Guru** 108630 points

    Hi Jason,

    Datasheet section 7.3.11 has the details.

    Please also read LMX2572EVM user's guide for an example.