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LMX2594: Phase adjustment in Integer mode.

Eric Naboulsi
Prodigy 40 points
Part Number: LMX2594

Hi,

I'm using two LMX2594 and I need to phase align them. Can it be done if the synthesizers are use in Integer mode and what registers do I need to programmed.

I don't use the OSC_2X bit and MULT features. My reference clock is 100MHz.

Thanks,

  • 0
    TI__Guru** 107260 points

    Hi Eric,

    With integer mode, it is belong to Cat. 1 or Cat. 2 SYNC, as described in Figure 27 in the datasheet.

    if CHDIV =1, no SYNC is required. If CHDIV not equal to 1, then simply make VCO_PHASE_SYNC = 1 and the devices will be synchronized.

    If CHDIV > 6, it is a Cat. 2 SYNC, again make VCO_PHASE_SYNC = 1 and then provide a pulse to the SYNC pin to complete sync. 

  • 0 in reply to Noel Fung
    Prodigy 40 points

    Hi Noel,

    I'm aware that when the VCO_PHASE_SYNC = 1 the chips will be synchronized. What I need is be able to change the phase of one LMX2594 refer to the reference clock.

    In the datasheet page 29, it said:

    1) Phase shift can be done with a FRAC_NUM = 0, but MASH_ORDER must be greater than zero

    2) For MASH_ORDER = 1, the phase shifting only occurs when MASH_SEED is a multiple of PLL_DEN.

    3) For the phase adjust, the condition PLL_DEN > PLL_NUM + MASH_SEED must be satisfied.

    So I assumed that (1) implied that it should work in Integer mode. (FRAC_NUM = 0), The issue I have is (2) contradict (3), how can I have MASH_SEED as a multiplier of PLL_DEN and PLL_DEN > MASH_SEED (if PLL_NUM = 0) in same time?

    Please can you confirmed that we can use phase shifting with MASH_ORDER = 1, PLL_NUM = 0 and how to calculate the phase shift.

    Regards,

    Eric 

  • 0 in reply to Eric Naboulsi
    TI__Guru** 107260 points

    Hi Eric,

    1) In an integer channel (NUM = 0), we can use any type of MASH_ORDER. For example, there is no performance difference when MASH_ORDER = 0 or  = 3 in an integer channel. 

    2) MASH_ORDER = 1 is seldom used, in fractional channel, MASH_ORDER = 2 or 3 are recommended. 

    In your case, you can set MASH_ORDER = 3 to get away from limitations 1) and 2). Use Equation 5 to calculate the phase shift.