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LMX2594: No SYSREF output on RFOUTBP

Part Number: LMX2594

I am not seeing any output when using SYSREF mode on RFOUTBP. I do see a notable difference in current being drawn from the power supply when OUTB_PD is unchecked or the SysREF output is not enabled, which seems to suggest that at least something is being driven internally, but I just do not see any output on an oscilloscope.

I believe I have set INPIN_IGNORE to low (unchecked in the GUI) and set the SysRefReq to high (checked in the GUI).

R112	0x700000
R111	0x6F0000
R110	0x6E0000
R109	0x6D0000
R108	0x6C0000
R107	0x6B0000
R106	0x6A0015
R105	0x699C40
R104	0x68C350
R103	0x67EB07
R102	0x663FFF
R101	0x650040
R100	0x64C350
R99	0x6314F9
R98	0x620001
R97	0x618800
R96	0x600028
R95	0x5F0000
R94	0x5E0000
R93	0x5D0000
R92	0x5C0000
R91	0x5B0000
R90	0x5A0000
R89	0x590000
R88	0x580000
R87	0x570000
R86	0x560000
R85	0x559000
R84	0x540001
R83	0x530000
R82	0x524400
R81	0x510000
R80	0x500000
R79	0x4F0100
R78	0x4E02DD
R77	0x4D0000
R76	0x4C000C
R75	0x4B0840
R74	0x4A0000
R73	0x49003F
R72	0x480049
R71	0x470029
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	0x3A0001
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	0x2DC0F2
R44	0x2C3263
R43	0x2B0000
R42	0x2A0000
R41	0x290000
R40	0x280000
R39	0x27FFFF
R38	0x26FFFF
R37	0x250404
R36	0x24003C
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	0x14F048
R19	0x1327B7
R18	0x120064
R17	0x1100DA
R16	0x100080
R15	0x0F064F
R14	0x0E1E70
R13	0x0D4000
R12	0x0C5002
R11	0x0B0018
R10	0x0A10D8
R9	0x090604
R8	0x082000
R7	0x0740B2
R6	0x06C802
R5	0x0500C8
R4	0x040A43
R3	0x030642
R2	0x020500
R1	0x010808
R0	0x00641C

  • Garret,

    The things to remember are:

    1. INPIN_IGNORE=0

    2. SysRefReqPin is high

    I think you did this, but I see the phase interpolator frequency is 3000 MHz, which is out of range.  I note that you want to divide 12 GHz down to 10 MHz and if you put the SysRef divider to DIV2 instead of DIV1, then you don't get the divide you want, but this might be the issue.  You might try at least to get an output with the correct value for SysRef Divider.  You can also get 10 MHz using the proper divide like Fvco = 7680, CHDIV = 4, SYSREF_DIV_PRE= DIV2, SYSREF_DIV = 48, fOUTB=10 MHz

    Also ensure the proper signal level on this output and try toggling the CE pin and the INPIN_IGNORE bit to ensure they are updated..

    REgards,

    Dean

  • Dean,

    Not having f_interpolator in the correct range (.8 GHz - 1.5 GHz) is what I believe was causing the problem since I had f_interpolator at 3 GHz. I did notice that the output would still work to some degree for f_interpolator < .8 Ghz.

    Thanks again,
  • Garret,

    OK, great. I will assume this issue is resolved, unless you say otherwise.

    Regards,
    Dean