LMX2571EVM: Changing spurious level

Mochi

Genius 3915 points

Part Number: LMX2571EVM
Other Parts Discussed in Thread: LMX2571

Hello,

Our customer is evaluating LMX2571 on the EVM then a strange phenomenon is observed.

Inputted 16.8MHz TCXO and output 900MHz. PLL output is very clean at initial as attached data.

After a while, it is about 4 min, the spurious signal level is increasing.

Then apply initialization, the spurious is go away and repeat same phenomenon after 4min.

Do you see any issue on registers setting or any other concern?

Regards,

Mochizuki

2571_900.tcs

over 1 year ago

0 Noel Fung over 1 year ago

TI__Guru* 88030 points

Hi Mochizuki-san,

I tried this configuration, I don't have the problem.

Since you are using TCXO, you should not enable the internal termination, this will overload the TCXO.

0 Mochi over 1 year ago in reply to Noel Fung

Genius 3915 points

Hi Noel,

Thank you very much for your advice.

We suggested the customer to try to remove internal termination.

So far no negative update is received.

Regards,

Mochizuki

0 Asim Khan over 1 year ago in reply to Mochi

TI__Genius 9250 points

Hi Mochi,

Let us know if there is any further help needed.

Best,

Asim

0 Mochi over 1 year ago in reply to Asim Khan

Genius 3915 points

Hi Asim and Noel,

Our customer has reported 36pin OSCin* connection was not correct in this evaluation.
Diff input mode is configured on IFBUF_SE_DIFF_SEL.
Because Diff input shows better spurious characteristics than SE input in their previous experiment.
TCXO output was inputted 34pin OSCin but 36pin OSCin* was left floating with 50ohm termination
When they connect it to GND then the issue is disappeared.
So the conclution is 36pin connection was not appropriate in this evaluation.

Regards,
Mochizuki

Clock & timing

Clock & timing forum

LMX2571EVM: Changing spurious level