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LMX2571: PLL_R_PRE_F1 = 2, output cannot locked properly

D L
Prodigy 10 points
Part Number: LMX2571
Other Parts Discussed in Thread: CODELOADER,

LMX2571 is used in synthesizer mode with internal VCO in our application.

Using Codeloader to config the LMX2571, the Auto Reload with Changes has been ticked.

- If PLL_R_PRE_F1 = 1, registers will be auto reloaded with adjusting output frequency.

- If PLL_R_PRE_F1 = 2, the registers cannot be auto reloaded with changes. 

   In this case, RESET must be set ON-->OFF, then using Ctrl+L to manually load the changes.

   Once manually loaded, then registers will be auto-reloaded with changes.

- Each time, when PLL_R_PRE_F1 was changed, the RESET most likely needs to be set ON-->OFF again, then LMX2571 could auto reload with changes thereafter.

This issue also happened with our auto test code. The LMX2571 won't lock properly while PLL_R_PRE_F1 changed.

Please see the screenshots of Codeloader below.

  • 0
    TI__Mastermind 28882 points

    Hi DL, 
    Codeloader is no longer supported. 
    TICSpro is the currently supported GUI to control/communicate with our clocking EVMs. 
    https://www.ti.com/tool/TICSPRO-SW

    Here is the LMX2571EVM user's guide - this is a quick start guide on getting up and running. 
    https://www.ti.com/lit/ug/snau176a/snau176a.pdf?ts=1706550555280&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FLMX2571EVM

    Regards, 

    Vicente 

  • 0
    TI__Guru** 106870 points

    Hi There,

    Since you are using the MULT, after Pre_R is change, you need to program R0 to do a calibration to the internal VCO as well as the MULT.

  • 0 in reply to Noel Fung
    Prodigy 10 points

    Hi,

    R0 bit[0] has been enable to calibrate each time when frequency changed.

    Is there any other bit to calibrate MULT?

    As this issue also happened on our auto test. For every frequency with PLL_PRE_R_F1=2, LMX2571 cannot lock properly.

    So, it shouldn't be a issue for using Codeloader.

  • 0 in reply to D L
    TI__Guru** 106870 points

    Hi DL,

    I tried but I don't see the problem.

    After changing Pre_R = 2, fpd is half. So we need to update PLL_N and PLL_NUM.

    my program sequence is:

    1. update Pre_R

    2. Update PLL_N

    3. Update PLL_NUM

    4. Program R0 once

    BTW, please note the restriction on using the MULT, there is an input, output frequency requirement to the MULT.

  • 0 in reply to Noel Fung
    Prodigy 10 points

    Hi, Noel.

    Could you help me to figure out what does these settings do? How did these change the registers of LMX2571?

    1. In TICS Pro, setting "Option -> Auto Update". 

    In Codeloader, "Option->Auto Reload with Change Ctrl+W".

    2. In TICS Pro, "USB Communications->Write All Registers Ctrl+L"

    In Codeloader, "Keyboard Controls-> Load Device Ctrl+L"

    Sometimes, if the value changed, "Auto Reload/Update" won't change the registers properly.

    I have to use "Ctrl+L" to make the settings take effect.

  • 0 in reply to D L
    TI__Guru** 106870 points

    Hi DL,

    Auto update: whenever you update a value, for example, change PreR value, then the corresponding register will be updated and TICS Pro will program that particular register once. You should see the traffic in the bottom left corner window.

    Usually only the first time programming after Vcc is applied or after a soft reset requires Ctrl+L to program all registers. After that, we only need to program those registers that we want to change. Remember, whenever the VCO frequency is change, we need to program R0 once to trigger the VCO calibration. For example, after programming a new PLL_N value, this register will be automatically updated and programmed. However, the output frequency is wrong because we need to manually program R0 to initiate a VCO calibration. TICS Pro will not program R0 for us automatically. In this case, if we do Ctrl+L, then the synthesizer will lock because all the registers including R0 will be programmed.