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LMX2592: LMX2592 Low temperature failure

user5848839
Prodigy 210 points
Part Number: LMX2592

Hi

I am using LMX2592 on my system and currently found that the lock cannot be set in the low temperature test. When the low-temperature recurrence failure occurs, LMX2592's own state has been abnormal, and the observed phenomena are:

1.Before the address is sent, MUXOUT has started to spit data.

2. After successful setting, MUXOUT outputs 1.5M periodic waveform;

Please help review my schematic  and register. Thanks! 

Schematic diagram as below. 

Register configuration as below.

static UINT32 g_sauiLmx2592InitRegData[]= {

        0x400077,
        0x3E0000,
        0x3D0001,
        0x3B0000,
        0x3003FD,
        0x2F08DE,
        0x2E1EA1,
        0x2D0096,
        0x2C0000,
        0x2B0000,
        0x2A0000,
        0x2900C8,
        0x280000,
        0x278104,
        0x260020,
        0x254000,
        0x240011,
        0x230219,
        0x22C3CA,
        0x212A0A,
        0x20210A,
        0x1F0401,
        0x1E0034,
        0x1D0084,
        0x1C2924,
        0x190000,
        0x180509,
        0x178842,
        0x162300,
        0x14012C,
        0x130965,
        0x0E0211,
        0x0D4000,
        0x0C7001,
        0x0B0018,
        0x0A1258,
        0x090302,
        0x081084,
        0x0728B2,
        0x041943,
        0x020500,
        0x010808,
        0x00231C

};

  • 0
    TI__Mastermind 33620 points

    Hi user5848839,

    • Can you tell us the approximate temperature where the issues are observed?
    • Are you using the MUXOUT pin for SPI readback when you observe the issue? I see the registers have configured MUXOUT for lock detect, so any kind of periodic signal on the MUXOUT pin when configured for lock detect is a sign that the PLL is becoming unlocked.
    • I can't read the picture clearly, do you have the 0.1µF capacitor on VTUNE_MID net populated? populating that capacitor could make the loop filter unstable.

    A few other things I noticed, unrelated to the issue:

    • Since you're only using the VCO path, you can write CHDIV_DIST_PD=1 (0x1F0481, instead of 0x1F0401) to save current
    • Since you're only using the VCO path, you can write CHDIV_SEG_SEL=0 (0x240001, instead of 0x240011) to save current

    Regards,