• State TI Thinks Resolved
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 21 subscribers
  • Views 76 views
  • Users 0 members are here
Support feedback
Options
Options
Related

LMX2572: Unable to obtain Lock Detect, bad readback values

GENEVIEVE RAWLINS
Prodigy 20 points
Part Number: LMX2572

Tool/software:

Good evening, 

I am having difficulty getting our LMX2572 to show Lock Detect as 1 either through the readback or via the pin. Reading the registers back, all values are as expected with the exception of the following regs:

r112: wrote 0x0000, returned status value 0xFEEC

r111: wrote 0x0000, returned status value 0x01B7

r110: wrote 0x0600, returned status value 0x0719

r109: wrote 0x0000, returned bad value 0x3800

r108: wrote 0x0000, returned bad value 0x00A1

r107: wrote 0x0000, returned bad value 0x8801

I would expect regs 110-112 to read back as non-zero values because these are status regs, but I can't rationalise why they would be these values. For instance, I would expect r110 [4:0] to be all 0's based on the datasheet.
Additionally, I did not expect r107-109 to have non-zero values. Is this normal? 
My config regs are below. We are using a custom board.
Thanks 
R125 0x7D2288
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 0x6E0600
R109 0x6D0000
R108 0x6C0000
R107 0x6B0000
R106 0x6A0007
R105 0x694440
R104 0x6809C4
R103 0x670000
R102 0x660000
R101 0x650000
R100 0x6409C4
R99 0x630000
R98 0x620000
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 0x550000
R84 0x540001
R83 0x53FFFF
R82 0x52FFFF
R81 0x510000
R80 0x500000
R79 0x4F0000
R78 0x4E00CF
R77 0x4D0000
R76 0x4C000C
R75 0x4B0800
R74 0x4A0000
R73 0x49003C
R72 0x480175
R71 0x47004D
R70 0x46C350
R69 0x450000
R68 0x4403E8
R67 0x430000
R66 0x4201F4
R65 0x410000
R64 0x401388
R63 0x3F0000
R62 0x3E00AF
R61 0x3D00A8
R60 0x3C000A
R59 0x3B0000
R58 0x3A6401
R57 0x390020
R56 0x380000
R55 0x370000
R54 0x360000
R53 0x350000
R52 0x340421
R51 0x330080
R50 0x320080
R49 0x314180
R48 0x3003E0
R47 0x2F0300
R46 0x2E07F2
R45 0x2DCE3C
R44 0x2C01C3
R43 0x2B0000
R42 0x2A0000
R41 0x290000
R40 0x280000
R39 0x270001
R38 0x260000
R37 0x250305
R36 0x240028
R35 0x230004
R34 0x220010
R33 0x211E01
R32 0x2005BF
R31 0x1FC3E6
R30 0x1E18A6
R29 0x1D0000
R28 0x1C0488
R27 0x1B0002
R26 0x1A0808
R25 0x190624
R24 0x18071A
R23 0x17007C
R22 0x160001
R21 0x150409
R20 0x147048
R19 0x1327B7
R18 0x120064
R17 0x1100EC
R16 0x100080
R15 0x0F060E
R14 0x0E1820
R13 0x0D4000
R12 0x0C5008
R11 0x0BB018
R10 0x0A1378
R9 0x090004
R8 0x082000
R7 0x0700B2
R6 0x062802
R5 0x0528C8
R4 0x040A43
R3 0x030782
R2 0x020500
R1 0x010808
R0 0x006298
  • 0
    TI__Guru** 107440 points

    Hi There,

    You cannot get MUXOUT pin high because you have set the MUXOUT pin as serial data output but not lock detect output. To set this pin as lock detect output, set MUXOUT_LD_SEL = 1.

    You cannot get correct lock status from register read back because you have set the lock detect mode to VCOCal. That is, as long as a VCO calibration is complete, lock detect will report lock. The read back register, rb_LD_VTUNE, however, determines lock according to the Vtune voltage. 

    In order to get correct read back lock status, set LD_TYPE to Vtune and VCOCAL. MUXout pin and read back will report lock only if a VCO calibration is completed and Vtune is within correct range.

    With your configuration and 100MHz input clock, my eval board can lock to 6GHz (LD_TYPE = 1).

    Register R110, R111 and R112 are read only registers, they contain other undisclosed register fields, it is normal that they may not read back 0.

  • 0 in reply to Noel Fung
    Prodigy 20 points

    Thanks for your detailed response and for verifying the registers. 

    You are right about the MUXOUT pin initially being used for serial data output, but what I forgot to say was that I then reprogram this to be LD out by setting r0 bit 3 to '1' and r59 bit 0 to '0'. With these settings would I not expect to see a lock signal going high after VCO calibration? I do not see this at all, which is concerning me. I have tried again with VCOCal and Vtune on MUXOUT pin and this also stays at '0'.

    Can I ask you to confirm which VCO is selected on your unit? My unit reports rb_VCO_SEL = 0x0, while rb_LD_VTUNE = 0x03, both of which indicate issues according to datasheet pg. 60.

    I will take another look at the hardware and make sure my power rails and clock source are as they should be.

  • 0 in reply to GENEVIEVE RAWLINS
    TI__Guru** 107440 points

    Hi Genevieve,

    With 100MHz input and your configuration, the VCO frequency is 6GHz. From read back, VCO6 is selected by calibration. This is the correct VCO core at 6GHz. Read back of 0 is not a valid data. There are 6 VCO cores in this device, we should read back 1 to 6.

    Looks to me that you are not getting calibration done correctly and the PLL is not locked. 

    Since the register configuration is correct, please check your hardware and check the SPI signal timing (with a scope). 

    A simple debug is, after Vcc power up the device, program POWERDOWN = 1, see if there is noticeable current drop. This action verifies if SPI communication is working.