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Original question:

LMX2572: Phase synchronization can not be achieved

LMX2572: Cannot sync RF outputs with SYNC line

David
Prodigy 10 points

Part Number: LMX2572LP

Tool/software: TI TICS PRO 1.7.7.6

I have 2 boards each with a LMX2572LP. Both are supplied with an identical 10Mhz input clock, and both are connected to one TI Reference Pro board, and both are programmed to output 200Mhz. Both are also supplied with an identical SYNC signal, which is 0 - 3V, on time of 733us, and period of 3 seconds. I'm able to program both parts simultaneously and see the 200Mhz output signals without issue. However, the SYNC functionality doesn't seem to work properly at all. I'm able to see both generators startup and run with random phase differences by toggling the POWERDOWN and/or reset bit in register R0, as expected, but the SYNC signal will either do nothing at all, or will create what seems like 1 of about 10 phase differences between the two signals every time it occurs (in this case every 3 seconds). 1 of those phase relationships is what I'm looking for--the two signals at the same phase--but it only happens randomly and occasionally. The settings I am using are shown below.

I have played around with MASH_RST_COUNT as well as all the other registers, but nothing I've tried seems to fix the issue--I can definitely make it worse, but not better.  

(All my cables and traces are very tightly length and impedance matched, so I don't think that's an issue. )

Any help would be VERY appreciated! 

  • 0
    Prodigy 10 points

    This is a dump of all the register settings I have now:

    R125	0x7D0820
R124	0x7C0000
R123	0x7B0000
R122	0x7A0000
R121	0x790000
R120	0x780000
R119	0x770000
R118	0x760000
R117	0x750000
R116	0x740000
R115	0x730000
R114	0x727802
R113	0x710000
R112	0x700000
R111	0x6F0000
R110	0x6E0000
R109	0x6D0000
R108	0x6C0000
R107	0x6B0000
R106	0x6A0007
R105	0x694440
R104	0x6803E8
R103	0x670000
R102	0x660000
R101	0x650000
R100	0x6403E8
R99	0x63AE14
R98	0x62011C
R97	0x610000
R96	0x600000
R95	0x5F0000
R94	0x5E0000
R93	0x5D0000
R92	0x5C0000
R91	0x5B0000
R90	0x5A0000
R89	0x590000
R88	0x580000
R87	0x570000
R86	0x560000
R85	0x552800
R84	0x540000
R83	0x53FFFF
R82	0x52FFFF
R81	0x510000
R80	0x500000
R79	0x4F0300
R78	0x4E0107
R77	0x4D0000
R76	0x4C000C
R75	0x4B0940
R74	0x4A0000
R73	0x49003F
R72	0x480001
R71	0x470081
R70	0x46C350
R69	0x450000
R68	0x4403E8
R67	0x430000
R66	0x4201F4
R65	0x410000
R64	0x401388
R63	0x3F0000
R62	0x3E00AF
R61	0x3D00A8
R60	0x3C03E8
R59	0x3B0001
R58	0x3A1001
R57	0x390020
R56	0x380000
R55	0x370000
R54	0x360000
R53	0x350000
R52	0x340421
R51	0x330080
R50	0x320080
R49	0x314180
R48	0x3003E0
R47	0x2F0300
R46	0x2E07F0
R45	0x2DC60A
R44	0x2C0A23
R43	0x2B0000
R42	0x2A0000
R41	0x290457
R40	0x280000
R39	0x270001
R38	0x260000
R37	0x258205
R36	0x2400A0
R35	0x230004
R34	0x220010
R33	0x211E01
R32	0x2005BF
R31	0x1FC3E6
R30	0x1E0CA6
R29	0x1D0000
R28	0x1C0488
R27	0x1B0002
R26	0x1A0808
R25	0x190624
R24	0x18071A
R23	0x17007C
R22	0x160001
R21	0x150409
R20	0x144848
R19	0x1327B7
R18	0x120064
R17	0x11008A
R16	0x100080
R15	0x0F060E
R14	0x0E1820
R13	0x0D4000
R12	0x0C5001
R11	0x0BB018
R10	0x0A10F8
R9	0x090004
R8	0x082000
R7	0x0700B2
R6	0x06C802
R5	0x0530C8
R4	0x040A43
R3	0x030782
R2	0x020500
R1	0x010800
R0	0x00601C

  • 0 in reply to David
    TI__Guru** 114760 points

    Hi David,

    This is a Cat.2 sync, you only need to keep VCO_PHASE_SYNC_EN = 1 all the time, then after programming, all devices will phase align. 

    I see in your configuration, PLL_DEN = 1 while you have enabled MASH_SEED and have a value greater than 1. This is not a valid configuration. I think MASH_SEED is making the trouble to you. 

  • 0 in reply to Noel Fung
    Prodigy 10 points

    Hi Noel, Thanks for your reply!

    I've tried disabling the MASH_SEED_EN, as well as setting it to 0, but this makes no difference. I have also tried setting the fractional denominator to 0, to 10000, and no change. When I pull the devices out of reset and write all registers they come up with random phases. 

  • 0 in reply to David
    TI__Guru** 114760 points

    Hi David,

    Is your 10MHz sine wave? Can you try with a square wave clock?

  • 0 in reply to Noel Fung
    Prodigy 10 points

    Hi Noel, I have been using a sine wave, but I just tried it with a 10Mhz 50% square wave and am getting exactly the same results. I also just tried it with a 5Mhz input square, both with and without the input doubler enabled, and same results. I've also tried varying the amplitude of the input clock and the only change I see is when it is too low and lock doesn't occur. 

    (Also, its worth mentioning that in between changes (input signal or register settings), I always reset both chips through the General Controls->Reset command, and then run the write all registers command. I can always see both outputs turn off when I issue the reset command, and then they come back up with random phases after writing all registers. I have both boards connected in parallel to one TI Ref Pro board (USB-SPI converter). 

  • 0 in reply to David
    TI__Guru** 114760 points

    Hi David,

    I think the RESET operation is causing the issue.

    This is actually a TICS Pro problem, not device problem.

    in TICS Pro, after programing RESET = 1. Do the following before de-assert the RESET.

    - in the menu bar, click Options, then uncheck AutoUpdate

    - Set RESET = 0 (this will not program the device)

    - again in the menu bar, click Options, then check AutoUpdate

    - Ctrl+L to program all registers

  • 0 in reply to Noel Fung
    Prodigy 10 points

    Hi Noel,

    From a quick test following your procedure, this does seem to make a difference, and I'm not able to reproduce the phase jumping every time I issue a SYNC signal.   But why??????

    in TICS Pro, after programing RESET = 1. Do the following before de-assert the RESET.   Register 00 is set to 601E

    - in the menu bar, click Options, then uncheck AutoUpdate          Nothing programmed

    - Set RESET = 0 (this will not program the device)         Nothing programmed

    - again in the menu bar, click Options, then check AutoUpdate     Nothing programmed

    - Ctrl+L to program all registers      All registers programmed, ending with reg 00 set to 601C

    Versus what I was doing previously:

    -Auto update on

    -Set RESET = 1.   Register 00 is set to 601E

    -Set RESET = 0.   Register 00 is set to 601C

    -program all registers   All registers programmed, ending with reg 00 set to 601C

    -and the phase now jumps around on nearly every SYNC pulse

     

    In all cases, the only value difference for Reg 00 is the RESET bit. 

    I won't say its solved just yet, since we'll have to test more (most notably using 2 separate USB_SPI converters), but this is looking hopeful. Thanks!