LMK04832: LMK04832

Shafeeq Muhammed

Part Number: LMK04832

Hi,

We are using LMK04832 in our design.
We are using 100MHz TCXO in OSCin.
And the outputs are 13.1072MHz, 23.04 MHz and 32.768MHz. all outputs are CMOS.

The VCO frequency is set 2949.12.

But when we are loading the configuration, the output frequency is not coming proper.

All output frequency is coming more than that of what we set.
For 13.172, 14.54 is coming
For 23.04, 27.35 is coming
For 32.768, 39,37 is coming.

We have seen below observation,

The SCORE showing in TICSPRO for 2949.12 VCO is 0.1
We have tried other VCO frequency with score more than 0.5 and the desired output is not coming. (Not our actual desired output, just generated few outputs to verify from set VCO).

Please let us know what is the SCORE and PDF2 value in frequency planner solution?
Also please suggest if the score is less than 0.5, whether LMK is not able to generate the set output?
If so, is there any other option to generate our required frequencies?

Please suggest.

Best Regards,
Shafeeq

over 3 years ago

0 vicente flores prado over 3 years ago

TI__Mastermind 32152 points

Hi Shafeeq,
Can you share your configuration (.tcs) file with me?

I don't think you can implement the above frequency plan given 13.1072 MHz is not divisible from the 100 MHz input. Thus I am not sure how you were able to have a solution generated?

Regards.

Vicente

0 vicente flores prado over 3 years ago in reply to vicente flores prado

TI__Mastermind 32152 points

Also,
LMK04832 does not support CMOS outputs? Are you positive you're using LMK04832?
update: my mistake, some outputs do support CMOS.

Regards,

Vicente

0 Shafeeq Muhammed over 3 years ago in reply to vicente flores prado

Expert 1220 points

Hi Vicente,

I have attached the configuration file.
I am generating 13.1072MHz, Not 13.172lmk_config.tcs

Also, as per the datasheet, LMK04832 supports CMOS outputs. (on clkout1, 3, 5, 7, 8, 9, 10, 11 & 13)

Best Regards,
Shafeeq

0 vicente flores prado over 3 years ago in reply to Shafeeq Muhammed

TI__Mastermind 32152 points

Hi Shafeeq,
LMK04832 N-Cal Divider value needs to match N divider value.
Please let me know if this solves your issue.

In your config I believe it was 625.

Regards,

Vicente

0 Shafeeq Muhammed over 3 years ago in reply to vicente flores prado

Expert 1220 points

Hi Vicente,

Sorry, I have attached the previous configuration file.
We have already tried this. But the issue is still there.

Best Regards,
Shafeeq

0 vicente flores prado over 3 years ago in reply to Shafeeq Muhammed

TI__Mastermind 32152 points

Hi Shafeeq,
Using your config I was able to get a lock using my EVM in lab but I have some questions..
Why are you using a 100 MHz input to generate the output frequencies you desire?
Those are two different frequency domains.
You would get optimal performance using a 122.88 MHz input or a integer multiple of that value. I suggest you switch from 100 MHz input to 122.88 MHz.

Using a 100 MHz input, did you design the loop filter accordingly given the very small 0.32 MHz PFD you're implementing? If the loop filter isn't designed accordingly, I would expect bad phase margin / locking issues.

Regards,

Vicente

0 vicente flores prado over 3 years ago in reply to vicente flores prado

TI__Mastermind 32152 points

One more question, are you using the EVM?

0 Shafeeq Muhammed over 3 years ago in reply to vicente flores prado

Expert 1220 points

HI Vicente,

We are using a existing setup. Previously we were generating 19.2Mhz using LMK. No we have changed the frequency as requirement changed. But the circuit remained same. I have not designed the loop filter accordingly. I have used the PLLATINUMSIM to calculate the values for loop filter for PLL2.

Can you confirm whatever I have done is correct. I have not used the PLLATINUMSIM before.
So that i will verify with the suggested loop filter.

Also I am not using the EVM, we are using LMK in a custom board

Best Regards,
Shafeeq

0 vicente flores prado over 3 years ago in reply to Shafeeq Muhammed

TI__Mastermind 32152 points

Hi Shafeeq,
I would change frequency of Fosc to 200 MHz given in your config you had the input doubler enabled.
Your N divider value was 9216 instead.

Regards,

Vicente

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LMK04832: LMK04832