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LMX2592: Problem with divider setting

Ryuji
Guru 20090 points
Part Number: LMX2592


Hello,

When we set the 7.1GHz VCO and total divide setting as 16, we can't get the expected frequency.
Please see the attached file as GUI screen shot and output capture.
In the GUI, output frequency should be 443.75MHz. Divider setting is same as datasheet table 4.
However, actual output frequency is 353MHz.
If we don't use output divider , there is no problem. We can get 7.1GHz output. There is the problem in output divider.

How to correct this operation ? Is this bug of the GUI?
We toggle FCAL_EN in the last setting. Also, if we use doubler and VCO frequency set as 3550MHz, the same problem is occurred.

Best Regards,
Ryuji

  • 0
    TI__Expert 8505 points
    Hi Ryuji,

    That is a correct observation. The channel divider should be used with the guideline of using the topmost combination in table4 of datasheet, and only moving down to the next combo if the division can no longer attain the desired frequency. The technical reason is that the CHDIV_SEG2 has some upper limitation and does not go all the way to 7.1GHz / 2 = 3.55GHz.