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Original question:

LMX2820: Release date

LMX2820: LMX2820EVM cannot lock between 11 and 11.2 GHz

0dBc
Prodigy 180 points
Part Number: LMX2820

Dear PLL Team,

I played with LMX2820EVM for some time. I realized that it is unable to lock between 11020 to 11200 MHz. I am using the "Default Mode 20-6-15" settings in TICS Pro software. I think the issue is somehow related to VCO calibration. I read back the rb_VCO_CAPCTRL (R74) as:

f=11000 ➝ 0x4A89BD
f=11010 ➝ 0x4A895D
f=11020 ➝ 0x4A201D  (PLL loses lock here)
f=11030 ➝ 0x4A201D  (PLL unlocked)
...
f=11200 ➝ 0x4A201D  (PLL still unlocked)

Somehow auto VCO calibration chooses VCO_CAPCTRL as 0 for 11020 ≤ f ≤ 11200 

I overwrote the VCO_CAPCTRL using the GUI (VCO_CAPCTRL_FORCE selected) and randomly varied it until PLL achieved lock. I was able to lock the PLL at 11200 MHz with VCO_CAPCTRL = 45.

So, how can I make the auto VCO calibration choose the correct value of VCO_CAPCTRL or 11020 ≤ f ≤ 11200 ? 

I attached my test setup photo, a screen-shot of TICS Pro software and EVM lot info tag on the box.

Thanks in advance.
Adnan 

  • 0
    TI__Guru* 81490 points

    Hi Adnan,

    We have seen that some prototype IC has issue with auto-calibration at the extreme frequency, I think you were seeing the same behavior. This issue will be fixed in the final silicon. The workaround is, as you did, manually adjust CAPCTRL to make it lock.

    Sorry for the inconvenient caused. 

  • 0 in reply to Noel Fung
    Prodigy 180 points

    Hi Noel,

    Thanks for your quick answer.

    1) When will TI release the final silicon? I would like to use this IC in a new design. 
    2) You said "some prototype IC has issue with auto-calibration at the extreme frequency". So if I replace the IC on the eval board with another PLMX2820 IC, will it work?
    3) Are you sure manually adjusting the CAPCTRL is a workaround? How can I know the value I choose will be good over temperature? PLL locks for a wide range of CAPCTRL values. 

  • 0 in reply to 0dBc
    TI__Guru* 81490 points

    Hi Adman,

    1. I am sorry that we cannot tell the release date in a public forum, please email to customer support site. 

    2. Probably, we did not screen in production, we cannot ensure the samples you get has no such issue.

    3. You can based on the readback value at 11020MHz. Change to the frequency you want, then adjust VCO_capctrl until the Vtune voltage is around 1.25V.