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LMX2571EVM: Start-up problem

Tuomas Haapala
Prodigy 40 points

Part Number: LMX2571EVM
Other Parts Discussed in Thread: LMX2571, USB2ANY

Hello!

I am using a micro-controller to interface with an LMX2571EVM. My code for LMX2571 register access seem to be working just fine.

When I try to start up (initialize) the LMX2571 by programming it for the first time after a reset, it gives me an unstable output waveform. I read all the registers afterwards to ensure that they were programmed correctly.

When I use CodeLoader4 and USB2ANY interface to initialize LMX2571 with the same settings after a reset, the PLL behaves perfectly. Afterwards, I read all the registers again with the micro-controller to ensure that they were programmed the same way as previously.

To eliminate any possible differences between the above two cases, I used the micro-controller as an SPI slave to read the data output of USB2ANY during initialization. In addition, I used an oscilloscope to check the approximate baud rate and the average delay between consecutive USB2ANY register access events. I then used the exactly same data, the same register access order and similar timing settings to initialize LMX2571 with the micro-controller but still ended up with the unstable output.

If I initialize LMX2571 with CodeLoade4 and USB2ANY first and then proceed to control LMX2571 with the micro-controller (change the loop divider value, output power levels, etc.), everything works perfectly.

In summary, I used CodeLoader4 and USB2ANY as a reference and ensured that the micro-controller does everything in the same way during initialization but still ended up with the crazy output waveform. I have no idea of what is causing the difference and why the PLL does not seem to start up properly. I was wondering if you have any suggestions?

Please find the initialization settings below. The data stream is the same for USB2Any and the micro-controller. A figure of the unstable output waveform is also attached.

Best regards, Tuomas

~~~

reset:
R18    0x5087
R17    0x7A11
R2     0x5087
R1     0x7A11
R0     0x22C3

initialize:
R60      0xA000
R58      0x8C00
R53     0x7806
R47     0x0000
R42     0x0210
R41     0x0810
R40     0x101C
R39     0x11F3
R35     0x0C83
R34     0x1803
R33     0x0000
R32     0x0000
R31     0x0000
R30     0x0000
R29     0x0000
R28     0x0000
R27     0x0000
R26     0x0000
R25     0x0000
R24     0x0408
R23     0x0084
R22     0x8584
R21     0x0101
R20     0x301B
R19     0x1200
R18     0x5087
R17     0x7A11
R16     0x0000
R15     0x0000
R14     0x0000
R13     0x0000
R12     0x0000
R11     0x0000
R10     0x0000
R9      0x0000
R8      0x0408
R7      0x0084
R6      0x8584
R5      0x0101
R4      0x3020
R3      0x1200
R2      0x5087
R1      0x7A11
R0      0x02C3


  • 0
    TI__Guru** 119660 points
    Hi Tuomas,

    I have no idea why it works with USB2ANY but it doesn't with a MCU.
    I checked your register setting, it looks fine although FIF2_INT is not necessary during initialization.
    During your RESET process, all you need to write is R0, other registers will be resumed to their silicon default value.
    The output plots look strange to me. The output should be a periodic signal, now it looks like a modulated signal. Are you doing FSK?
  • 0 in reply to Noel Fung
    Prodigy 40 points
    Hi Noel!

    Thank you for your message.

    There should be no FSK. After initialization, the LMX2571 is set to FSK SPI FAST mode and I am not accessing any registers in the figures. I agree that the output looks strange, it does not look like the PLL is locked (although if I change MUXout pin functionality to lock detect, it gives me 'locked, HIGH'). My hope was that the output waveform would point to some specific issue that an experienced LMX2571 user might recognize.

    Best, Tuomas
  • 0 in reply to Tuomas Haapala
    TI__Guru** 119660 points
    Hi Tuomas,

    At the moment, I am afraid I don't have any specific advice I can provide to you. Maybe you can try, instead of writing all register in one shot, write each register one by one and observe the response from the chip after each register write. Compare the result using MCU and TICS Pro method. Hopefully you can pin point which register write has created the problem.
  • 0 in reply to Noel Fung
    Prodigy 40 points
    Hi Noel,

    I had to remove my measurement setup for a couple of weeks. I will perform the test you suggested once I have everything set back up.

    Best, Tuomas
  • 0 in reply to Tuomas Haapala
    TI__Guru** 119660 points
    Hi Tumoas,

    OK, I will close this post for now. You can place a new post once you have an update.