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LMX2594: LMX2594 lock problem

user6270634
Prodigy 120 points
Part Number: LMX2594

Hi team,

This is Nur. I am working on LMX2594 chip now. We designed an  LMX2594 EVM using the pll chip. When I want LMX2594 EVM to produce any frequency in the range of 10MHz to 1.5 GHz, it can't. But above 1.5 Ghz , it works porfectly. While designing this board, we consider LMX2594 datasheet and loop filter.

I am using TI control board and TICSPRO software to control our LMX2594 EVM .

I would be appreciated for your help.

Thanks.

  • 0
    TI__Genius 11900 points

    Hello Nur,

    The lower output frequencies can be generated by using the channel divider. Have you considered this? Can you send me a screenshot of an example where you have configured it to the frequency in the range 10 MHz to 1.5 GHz that does not work?

    Thanks,

    Vibhu

  • 0
    Prodigy 120 points

    For instance I couldn't see 1Ghz using this TICS PRO configuration and TI control board.

  • 0 in reply to user6270634
    TI__Guru** 108480 points

    Hi Nur,

    I cannot see any problem with this configuration.

    Can you verify:

    1. Vcc power up the board

    2. Ensure a valid reference clock is ready

    3. Go to the User Controls page. Check RESET and then uncheck RESET

    4. With this configuration, CTRL+L to load all the registers

    Check:

    - is it lock?

    - do you get 1GHz signal?

    - change the Channel Divider to 4, do you get 2GHz signal? 

  • 0 in reply to Noel Fung
    Prodigy 120 points

    Hello,

    1. Yes I control the power . it is ok.

    2. Yes I can see 100 Mhz reference clock.

    3. I did it.

    4.  I did it

    Check:

    -  there is no signal in the spectrum even with full span.

    - I did not get 1Ghz signal.

    - In the same configuration and test setup ,when I changed the Channel Divider to 4, I got 2GHz signal. No problem for 1.3 Ghz 1.4 Ghz 1.5 Ghz .

    The problem appears from 10 Mhz to 1.3 Ghz , I think.

  • 0 in reply to user6270634
    TI__Genius 11900 points

    Hello Nur,

    As a sanity check can you do the above after you change the R divider value from 0 to 1.

    Also can you try this:

    1. Load "Default configuration"
    2. Go to the User Controls page. Check RESET and then uncheck RESET
    3. CTRL+L to load all the registers
    4. Do you see 7 GHz?
    5. Change channel divider to large value say 64
    6. Do you see 218.75 MHz?

    Thanks,

    Vibhu

  • 0 in reply to Vibhu Vanjari
    Prodigy 120 points

    1. Loaded "Default configuration"
    2. Went to the User Controls page. Checked RESET and then unchecked RESET
    3.  Loaded all the registers
    4. I could see  7 GHz
    5. Changed channel divider to large value = 64
    6. I did not see  218.75 MHz. Because the Fvco was 14000. So I could not choose the channel div great of 8 . ( Fvco must be <11500 for channel div>=8 ) So this configuration is not recommended.

    I solved my problem.It was about power. Thanks .