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LMK04821EVM: unlocked issue analysis

Adrian Liu
Intellectual 1580 points
Part Number: LMK04821EVM

Hi Team,

In customer use case, CLKIN=40MHz,OSCin=30.72MHz, PLL2 VCO=2000MHz, I meet some problems when setting this configuration.

LMK04821EVM cannot lock under the following configuration, please help with it, thank you.

in40 ocsin30_72 out1000 unlock.txt
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R0 (INIT) 0x000090
R0 0x000010
R2 0x000200
R3 0x000306
R4 0x0004D0
R5 0x00055B
R6 0x000600
R12 0x000C51
R13 0x000D04
R256 0x010002
R257 0x010155
R258 0x010255
R259 0x010301
R260 0x010402
R261 0x010500
R262 0x0106F1
R263 0x010755
R264 0x010802
R265 0x010955
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

BR

Adrian

  • 0
    TI__Genius 10985 points

    Hello Adrian,

    After importing your hex file with your specified values (assuming both CLKin0 and CLKin1 are 40MHz), there seems to be no problem on the frequency planning on my end. Therefore, I'm assuming there's a problem with your loop filter. Could you send me your topology and values you implemented for its components? Also, if possible, next time please attach the .tcs file, it makes it easier for me to debug. Please look at the picture below that shows where you click to save a .tcs file from TICS Pro.

    Thanks,

    Andrea

  • 0 in reply to Andrea Vallenilla
    TI__Intellectual 1580 points

    Hi Andrea,

                     Thanks for your reply. For the question you mentioned above,

                      (1) Customer did not change the topology of loop filter on EVM board. The topology and values are the default setting in the user guide as below.

                      (2) The .tcs file for the configuration is attached below, in this configuration, we can't config the EVB to locked. Please check

    clkin40 oscin3072 clkout1000 unlock-2.tcs

    Thanks 

    Adrian

  • 0 in reply to Adrian Liu
    TI__Genius 10985 points

    Hello Adrian,

    I will get back to you later. 

    Thanks,

    Andrea

  • 0 in reply to Andrea Vallenilla
    TI__Genius 10985 points

    Hello Adrian,

    The VCXO that you are using, is it the one on the board or are you using another one? If so, how did you include that VCXO to the board, i.e did you solder it into the EVM, do you have a separate board for the VCXO?

    I would like to note that if you are using the VCXO that comes already assembled into to EVM then your OSCin frequency has to be 122.88 MHz. To make the board assembled VCXO lock, it needs to receive a 122.88 MHz input, which is not the case based on your config. Why do you need a 30.72 MHz OSCin signal?

    Thanks,

    Andrea