LMX2531: Output clock frequency fluctuation

masahiko shimizu

Part Number: LMX2531

Hi,

My cutomer is using LMX2531LQ2570E.
He has issue of output clock frequency fluctuation.
Please see the below picture.
The output frequency of LMX2531 fluctuates every 70 sec.

What is the cause of this issue?
Could you give advice me, please?

Customer register condition is below.

Input frequency : 10MHz
Register setting :
840005
800005
8007F5
01048C
000BA9
028018
021707
460056
3C0004
FCE623
568022
3E2191
6D1C00

Best regards,
Shimizu

over 6 years ago

0 Brian Wang over 6 years ago

TI__Expert 7855 points

Hi Masahiko,

Thank you for the description and plot and also exact settings. Is this with TI's Evaluation Module or on customer board?

0 masahiko shimizu over 6 years ago in reply to Brian Wang

Guru 11235 points

Hi Brian,

This is with customer board.
Please see the below.
Customer confirmed with signal generator, too.
Using signal generator without LMX2531, this issue doesn't occur.

Best regards,
Shimizu

0 masahiko shimizu over 6 years ago in reply to masahiko shimizu

Guru 11235 points

Hi Brian,

How is the progress about this?

Best regards,
Shimizu

0 Brian Wang over 6 years ago in reply to masahiko shimizu

TI__Expert 7855 points

Shimizu,

We discussed here, it should be a system related coupling. The Sig Gen will no show because it is isolated with the rest of the board. But the LMX2531, being internal on the board can have coupled noise, and something periodic like 70seconds seem like some reoccurring action from some device on the board. They don't see this on a normal standalone EVM right?

Regards,

Brian Wang

Clock & timing

Clock & timing forum

LMX2531: Output clock frequency fluctuation