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LMX2582: Oerating conditions in output dividers

user6293841
Prodigy 110 points
Part Number: LMX2582

Tool/software:

Some of LMX2582 devices do not divide correctly 7011.2MHz VCO, under the settings of CHDIV_SEG1: divide-by2, CHDIV_SEG2: divide-by8, CHDIV_SEG3: - (REG35: 0x109B, REG36: 0x0420). Others devices divide correctly.
In both cases, lock detectors indicate 'Locked', so output diviers seem not work correctly in some devices.

When I change the divider settings to CHDIV_SEG1: divide-by2, CHDIV_SEG2: divide-by4, CHDIV_SEG3: divide-by2 (REG35: 0x059B, REG36: 0x0441), devices work correctly.
At VCO frequency of 6627.2MHz, 6819MHz diveices work correctly.

Are these defective or does the divider have operating conditions?

  • 0
    TI__Guru** 108130 points

    Hi Ashida-san,

    If you need 4xx MHz, you should use a lower VCO frequency. Datasheet has the following:

  • 0 in reply to Noel Fung
    Prodigy 110 points

    Dear Fung,
    Thank you for your comment.
    Does VCO FREQUENCY in table 7-4 show the restrictions on the maximum VCO frequency?
    If so, in 2020 (before datasheet revision E is not issued..), using SEG1=2, SEG2=2 for 1414MHz output is accepted.
    e2e.ti.com/.../
    Is this use case not acceptable now?

  • 0 in reply to user6293841
    Prodigy 110 points

    Dear Fung,
    The Table7-4 suggests the setting of SEG1=3, SEG2=1, SEG3=1, in case of 1540MHz output.
    I tried with 2 settngs.
    Dividers do not work correctly with setting of SEG1=3, SEG2=1, SEG3=1 and VCO=4620MHz, but dividers work correctly with setting of SEG1=2, SEG2=2, SEG3=1 and VCO=6160MHz.
    The former setting is within the range of the table7-4, and the latter setting is outside of the range.
    What shoul I refer to ??

  • 0 in reply to user6293841
    TI__Guru** 108130 points

    Hi Ashida-san,

    My board works with both configurations.

    With SEG1=3, SEG2=1, SEG3=1 and VCO = 4620MHz, are you not getting output in all devices or only in the same devices that you have reported having issues?

    FYI, below is the register setting in my setup.

    Fullscreen LMX2582_4620MHz.txt Download 
    R70	0x460000
R69	0x450000
R68	0x440089
R64	0x400077
R62	0x3E0000
R61	0x3D0001
R59	0x3B0000
R48	0x3003FC
R47	0x2F00CF
R46	0x2E0FA3
R45	0x2D0064
R44	0x2C0000
R43	0x2B0000
R42	0x2A0000
R41	0x2903E8
R40	0x280000
R39	0x278204
R38	0x26002E
R37	0x254000
R36	0x240411
R35	0x23021F
R34	0x22C3EA
R33	0x212A0A
R32	0x20210A
R31	0x1F0601
R30	0x1E0034
R29	0x1D0084
R28	0x1C2924
R25	0x190000
R24	0x180509
R23	0x178842
R22	0x162300
R20	0x14012C
R19	0x130965
R14	0x0E018C
R13	0x0D4000
R12	0x0C7001
R11	0x0B0018
R10	0x0A10D8
R9	0x090302
R8	0x081084
R7	0x0728B2
R4	0x041943
R2	0x020500
R1	0x010808
R0	0x00221C

  • 0 in reply to Noel Fung
    Prodigy 110 points

    Dear Fung,
    I am sorry for my miss judgement. My boards work with both configurations. The problem is in the following circuit.

    The output of LMX2582 drives a quadrature generator with a divide-by-2 method. I need  180-15400MHz output from divide-by-2/4/8. A divide-by3 output causes a large quadrature phase error in the following circuit.
    Are cofigurations such as SEG1=2, SEG2=2 and 1184-1540MHz of output frequecy available?
    e2e.ti.com/.../

  • 0 in reply to user6293841
    TI__Guru** 108130 points

    Hi Ashida-san,

    So your problem is your system is not happy with odd divider output, this makes sense. 

    If your required frequencies are between 1184MHz and 1540MHz, I think it is fine to use SEG1=SEG2=2 to get divide by 4. 

  • 0 in reply to Noel Fung
    Prodigy 110 points

    Dear Fung,

    Of course, I want to use SEG1=SEG2=2 for over 1184MHz. But you mention about the restrictions of the maximum VCO frequency for each divider, and output frequency over 1184MHz with SEG1=SEG2=2 is outside of the range of Table7-4. Is this configuration is acceptable ??

  • 0 in reply to user6293841
    TI__Guru** 108130 points

    Hi Ashida-san,

    The max. input frequency to SEG2 is approx. 3.3GHz. So SEG1=SEG2=2 is a valid configuration, as long as the output frequency is limited to 1540MHz.

    In general, we recommend follow Table 7-4, this would return predictable result. 

  • 0 in reply to Noel Fung
    Prodigy 110 points

    Dear Fung,

    Thank you for information about the max. input frequency to SEG2 . I use SEG1=SEG2=2 configuration. for 1184-1540MHz without worry.

    Regards.