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LMX2594: Inappropriate frequencies are sometimes generated

user5788058
Intellectual 410 points
Part Number: LMX2594

Hi,

I am currently starting up a PCB equipped with LMX 2594.

Even though I set the appropriate values in the registers, I sometimes have a problem that I can't get the expected frequency.

If the problem occurs every time, I can conclude that the value I set is wrong, but it only happens occasionally.

I checked the register settings related to frequency and output by reading them back when there was a strange frequency, but I couldn't see any difference from the settings made by TICSPro.

In most cases, the output is normal, so I don't think there is any problem with the setting.

Is it possible that the expected output is not obtained sometimes even though there is no problem in the set value?

I have no idea what's going on. If you have any ideas, please let me know.

  • 0
    TI__Guru* 81490 points

    Hi There,

    Could you send us your TICS Pro configuration?

  • 0 in reply to Noel Fung
    Intellectual 410 points

    Hi,There,

    The register values I set are as follows.

    R112 0x700000
    R111 0x6F0000
    R110 0x6E0000
    R109 0x6D0000
    R108 0x6C0000
    R107 0x6B0000
    R106 0x6A0001
    R105 0x690021
    R104 0x680000
    R103 0x67B13B
    R102 0x663E13
    R101 0x650011
    R100 0x640000
    R99 0x634EC5
    R98 0x6207B0
    R97 0x610888
    R96 0x600000
    R95 0x5F0000
    R94 0x5E0000
    R93 0x5D0000
    R92 0x5C0000
    R91 0x5B0000
    R90 0x5A0000
    R89 0x590000
    R88 0x580000
    R87 0x570000
    R86 0x565F6F
    R85 0x552E27
    R84 0x540000
    R83 0x53FFFF
    R82 0x52FFFF
    R81 0x510000
    R80 0x50B13B
    R79 0x4F0093
    R78 0x4E0097
    R77 0x4D0000
    R76 0x4C000C
    R75 0x4B0800
    R74 0x4A0000
    R73 0x4906E4
    R72 0x480008
    R71 0x470049
    R70 0x46C350
    R69 0x450000
    R68 0x4403E8
    R67 0x430000
    R66 0x4201F4
    R65 0x410000
    R64 0x401388
    R63 0x3F0000
    R62 0x3E0322
    R61 0x3D00A8
    R60 0x3C0000
    R59 0x3B0001
    R58 0x3A1001
    R57 0x390020
    R56 0x380000
    R55 0x370000
    R54 0x360000
    R53 0x350000
    R52 0x340820
    R51 0x330080
    R50 0x320000
    R49 0x314180
    R48 0x300300
    R47 0x2F0300
    R46 0x2E07FE
    R45 0x2DC0DF
    R44 0x2C1F23
    R43 0x2B0000
    R42 0x2A0000
    R41 0x290000
    R40 0x280000
    R39 0x27FFFF
    R38 0x26FFFF
    R37 0x250404
    R36 0x240032
    R35 0x230004
    R34 0x220000
    R33 0x211E21
    R32 0x200393
    R31 0x1F43EC
    R30 0x1E318C
    R29 0x1D318C
    R28 0x1C0488
    R27 0x1B0002
    R26 0x1A0DB0
    R25 0x190C2B
    R24 0x18071A
    R23 0x17007C
    R22 0x160001
    R21 0x150401
    R20 0x14D848
    R19 0x1327B7
    R18 0x120064
    R17 0x110108
    R16 0x100080
    R15 0x0F064F
    R14 0x0E1E70
    R13 0x0D4000
    R12 0x0C5005
    R11 0x0B0018
    R10 0x0A10D8
    R9 0x090604
    R8 0x082000
    R7 0x0740B2
    R6 0x06C802
    R5 0x0500C8
    R4 0x040D43
    R3 0x030642
    R2 0x020500
    R1 0x010809
    R0 0x006418

  • 0 in reply to user5788058
    Intellectual 410 points

    Hi,

    I called back all registers to see the value when LMX was able to generate the desired frequency or not. When it worked, the R111 was 0x0040. But when things didn't work out, the R111 was 0x0055. In the datasheet, R111 is described as rb_VCO_CAPCTRL.
    All other writable registers did not differ from the values I set.
    In the current setup, the VCO calibration Speed Assistance Level is set to No Assist. Will changing this solve the problem?

  • 0 in reply to user5788058
    TI__Mastermind 27581 points

    Hi,

    The bits for rb_VCO_SEL, rb_VCO_DACISET, and rb_VCO_CAPCTRL are in these higher registers.  They are readback and related to the VCO calibration.

    So what could be happening is that the VCO is calibrating to the wrong value.  If this happens, then it will not recover.   You can try the following:

    1.Increase the value of CAL_CLK_DIV to slow the calibration clock

    2. When it fails, program the R0 register 1 more time (with FCAL_EN=1) to redo the calibration

    3. When you first power up the device, ensure that you are waiting long enough for the LDOs to stabilize before you program register R0 to run the VCO calibration.  Otherwise, the calibration runs based on incorrect voltage bias levels and comes back in error.

    Regards,
    Dean