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LMX2820: SROUT only generate DC signal

Part Number: LMX2820

Hi,

I am trying to generate 125 MHz SROUT output as well as my 2 GHz in RFOUTA (setting attached) LMX2820_SROUT125M.tcs

I got expected output in my RFOUTA but I only got DC output in my SROUT.

I follow the setting for SROUT as per the EVM user guide. 

Could you kindly check what did I miss from the setting?

Best regards,

Andri Haryono

  • Hi Andri,

    I think I forgot to mention that the SRREQ pin needs to be HIGH. In User Controls page, check the SRREQ box. Let us know if you still cannot get a clock out from SROUT.

  • Hi,

    I have enabled the SRREQ, but I still did not get the correct signal. Do I need to provide certain input to the SRREQ?

    Best regards,

    Andri Haryono

  • Hi Andri,

    After setting up the configuration in the PLL page, go to the User Controls page to enable SRREQ pin, then SROUT will be generated. Please try disable and then enable SRREQ pin to see if you have the SROUT clock. Meanwhile, I will ask my colleague to verify it.

  • Hi, I have tried your suggestion, but still no luck.

    Could you kindly share the tcs file that have a confirmed SROUT signal.

    I have 3 EVMs and check them all.  I am sure it is a config issue.

  • Andri,

    Can you check the state of register R64 bit 14? This bit should be zero for SYSREF to work.

    Regards,

    Derek Payne

  • R122	0x7A0000
    R121	0x790000
    R120	0x780000
    R119	0x770000
    R118	0x760000
    R117	0x750000
    R116	0x740000
    R115	0x730000
    R114	0x720000
    R113	0x710000
    R112	0x70FFFF
    R111	0x6F0000
    R110	0x6E001F
    R109	0x6D0000
    R108	0x6C0000
    R107	0x6B0000
    R106	0x6A0000
    R105	0x69000A
    R104	0x680014
    R103	0x670014
    R102	0x660028
    R101	0x6503E8
    R100	0x640533
    R99	0x6319B9
    R98	0x621C80
    R97	0x610000
    R96	0x6017F8
    R95	0x5F0000
    R94	0x5E0000
    R93	0x5D1000
    R92	0x5C0000
    R91	0x5B0000
    R90	0x5A0000
    R89	0x590000
    R88	0x5803FF
    R87	0x57FF00
    R86	0x560040
    R85	0x550000
    R84	0x540040
    R83	0x530F00
    R82	0x520000
    R81	0x510000
    R80	0x500040
    R79	0x4F0108
    R78	0x4E0000
    R77	0x4D0608
    R76	0x4C0259
    R75	0x4B0154
    R74	0x4A9431
    R73	0x490000
    R72	0x480000
    R71	0x470000
    R70	0x4600FE
    R69	0x450001
    R68	0x440000
    R67	0x43F000
    R66	0x42003F
    R65	0x410000
    R64	0x404184
    R63	0x3FC350
    R62	0x3E0000
    R61	0x3D03E8
    R60	0x3C01F4
    R59	0x3B1388
    R58	0x3A0000
    R57	0x390001
    R56	0x380001
    R55	0x370002
    R54	0x360000
    R53	0x350000
    R52	0x340000
    R51	0x33203F
    R50	0x320080
    R49	0x310000
    R48	0x304180
    R47	0x2F0300
    R46	0x2E0300
    R45	0x2D0000
    R44	0x2C0000
    R43	0x2B0000
    R42	0x2A0000
    R41	0x290000
    R40	0x280000
    R39	0x270004
    R38	0x260000
    R37	0x250500
    R36	0x240028
    R35	0x233000
    R34	0x220010
    R33	0x210000
    R32	0x201241
    R31	0x1F0401
    R30	0x1EB18C
    R29	0x1D318C
    R28	0x1C0639
    R27	0x1B8001
    R26	0x1A0DB0
    R25	0x190624
    R24	0x180E34
    R23	0x171102
    R22	0x16E2BF
    R21	0x151C64
    R20	0x14272C
    R19	0x132138
    R18	0x120000
    R17	0x1115C0
    R16	0x10171C
    R15	0x0F2001
    R14	0x0E3001
    R13	0x0D0038
    R12	0x0C0408
    R11	0x0B0612
    R10	0x0A0000
    R9	0x090005
    R8	0x08C802
    R7	0x070000
    R6	0x060A43
    R5	0x050032
    R4	0x044204
    R3	0x030041
    R2	0x0281F4
    R1	0x01D780
    R0	0x006470
    

    Hi, Please find the register value attached.

    the R64 bit 14 is 0.

    Is there anything else that possibly cause this?

  • Hi Andri,

    Your register is showing R64=0x404184, so bit 14 is 1. Please change this bit to 0, program all the registers once and then make SRREQ pin L-->H.

  • Hi,

    I changed R64=0x400184, the write all register, then set SRREQ from L -> H.

    But still SYSRER is DC

  • Hi Andri,

    My colleague has verified this, he could get sysref signal out with the following sequence. Would you please try again? BTW, what is the marking on the surface of the device?

    1. Lock the device to the desired frequency (with R64[14]=0)
    2. Make SYSREF_EN = 1 (and PHASE_SYNC_EN = 1)
    3. Make SROUT_PD = 0
    4. Make SRREQ pin = HIGH
  • Hi, I have retried that sequence. but still no luck
    I have confirm the output using oscilloscope as well as a signal analyzer.

    which marking you are referring?

    if I get you correctly. in the board it says

    HSDC060A

    LMX2820EVM

    6521400153

    Can you share with me you config file?

  • Hi Andri,

    Your above configuration register settings are good, except change SYSREF_INP_FMT --> CMOS and R64=0x400184. With this, you should get SYSREF output.

    Otherwise, you can go ahead with the default configuration and follow the below steps:

    1. Lock the device to the desired frequency (with R64[14]=0)
    2. Make SYSREF_EN = 1 (and PHASE_SYNC_EN = 1)
    3. Make SROUT_PD = 0
    4. Make SRREQ pin = HIGH

    Thanks!

    Regards,

    Ajeet Pal