LMK5B33216EVM: DPLL lock to 1pps not working

Hi Youngho,

When using DPLL, XO should have non-integer relationship to the BAW VCO3 of 2500 MHz. You have 100 MHz XO here. What is your PDF?

-Riley

Hello Riley,

My APLL3 PDF is 66.66666MHz. I check lock status from "status" page. When I click the "Read status" DPLL3 LOPL_DPLL3, LOFL_DPLL3, and HLDOVR3 are all checked when I tried with 1Hz (0.000001MHz) clock input at REF0. But with 1MHz input, the check mark is gone and looks like it is locked. FYI, "start page" step 6 DPLL3 setting is as follows. DPLL LBW: 10Hz, DPLL transfer function allowed peaking: 0.1dB, DPLL error Function allowed peaking: 1dB, DCO step size: 0.1ppb, transfer function attenuation: 100, error function attenuation: 100.

Also, at "inputs" page, DPLL3: BAW waring said "No input selected! Holdover!" can you please recommend what to do to make DPLL3 locked to 1Hz?

Thanks,

Hi Youngho,

This warning means the reference is not detected. When this happened, on the Status page, do you see REF0 is validated and DPLL3 also selects REF0?

-Riley

Riley,

No, Reference validation is not checked at all and RFE0 was not selected but all holdover.

I did some more experiments with reference clock frequencies. 25MHz, 1MHz, 0.9MHz, 0.8MHz and 0.7MHz could be locked with 10Hz DPLL3 loop BW. I can see Ref0 validation and DPLL3 chose RFE0 at the status page.

Once the frequency goes down below 0.7MHz such as 0.65MHz, 0.6MHz..etc, it starts to fail to lock. I tried PLL3 loop BWs with 10Hz, 20Hz, 50Hz, 100Hz, 300Hz but no luck. Do I need to do something at validation page? If you have tried with 1-pps lock with PDF of 66.66666MHz, can you please share your setting? it is very frustrating to make this work.

thank you.

Hi Youngho,

I do not have 1-PPS config with PDF 66.666 MHz. I understand getting 1-PPS to lock is a bit tricky with the settings. I'm checking internally with my team and will do some testing and get back to you.

-Riley

Hi Riley,

Have you tried 1-pps config with PDF of 66.6666MHz? My output is 156.25MHz at port 4. Can you share your configuration if it worked out? Thanks,

Hi Youngho,

There are a few internal registers that I need to set for 1-PPS. Currently I have 1-PPS config at 96-MHz PDF and am looking into optimizing it for your use case. I will provide the .tcs file by next week.

-Riley

Hello Riley,

Thanks for the comments. FYI, my XO is 100MHz. I am not sure how to make PDF of 96MHz out of it. If you can make something different PDF out of 100MHz, that will be great. I will look forward to this.

Best,

Hi Youngho,

Yes, I will adjust the config to your use case 100 MHz XO and 66.66 MHz PDF.

-Riley

Riley,

Thanks for this. I will test it soon. One thing I found the script has 0.5MHz input, not 1Hz. Will 1Hz still work with it or do you have another file that has configured with 1Hz input? Thanks,

Hi Youngho,

When loading the file, what frequency is loaded in the reference? I have set it up at 1-PPS REF0 (IN0)

-Riley

Also, please use the latest TICS Pro version on ti.com

-Riley

This is what I have when I open the script. Can you confirm if the right file was updated?

I have seen 0.5MHz, not 1e-06. Can you please double check and upload the right file?

Yes, I just updated the TicsPro with the new one. It still showed the script with 0.5MHz Ref0 frequency.

What TICS Pro version are you using? You can see it in Help -> About section.

When I load the file, it is 1-PPS. I need to investigate this issue. In the mean time, please try:

- change the input reference to 1e-06

- check DPLL3 LBW is at 0.1 Hz

- match these settings for REF0 on validation page

- run the VCO calculation with these 4 buttons then "Write All Regs" and "Soft-reset Chip"

- check if REF0 is valid. If the input is valid, the device will start locking.

-Riley