LMK00301: Output switching time

Doug Snook

Prodigy 10 points

Part Number: LMK00301

Tool/software:

What is the expected switching time (new output after changing CLKin_SEL) for the LMK00301?

Normally I am observing a very fast switching time, but occasionally I see about 12 usec, which seems long.

Thanks

7 months ago

0 William Pfennigwerth 7 months ago

TI__Expert 8401 points

Hello,

Sorry for the delay. I will try to get back to you tomorrow.

Regards,

Will

0 William Pfennigwerth 7 months ago in reply to William Pfennigwerth

TI__Expert 8401 points

Doug,

Sorry for the long delay. Unfortunately, we do not have a specification on switching time as the internal switching architecture is asynchronous and therefore the output being valid will depend on the two frequencies being switched, their phases, and the particular moment that the switch occurs. What is the nominal switching time that you are seeing? Could you send scope captures of both?

Regards,

Will

0 Doug Snook 7 months ago

Prodigy 10 points

Will,

Thanks for the response. I don't have easy access to scope photos to send. The situation is switching with the LMK00301 between two different clock sources, both in the 60 MHz range. The LMK00301 output goes into a clock detection circuit using a 100 MHz clock to sample the signal. I was wondering about the LMK00301 switching to rule out some issues. Is there a nominal switching time between two similar frequency inputs?

Thanks,

Doug

0 William Pfennigwerth 7 months ago in reply to Doug Snook

TI__Expert 8401 points

Doug,

I will setup a a test tomorrow with two 60MHz inputs and switch it several times to try to get you an average estimated switching time.

Regards,

Will

0 Doug Snook 7 months ago in reply to William Pfennigwerth

Prodigy 10 points

Thanks. I appreciate your help. Doug

0 William Pfennigwerth 7 months ago in reply to Doug Snook

TI__Expert 8401 points

Doug,

I took 20 random measurements just to give you an idea and here is what I found.

Setup: 2 independent inputs at 60MHz, CLKin_SEL triggered randomly 20x, measured the time from CLKin_SEL logic low threshold (400mV) to functional clock output.

Min: 6.6ns

Mean: 14.6ns

Max: 21.2ns

It seems that it least takes a few clock cycles to cleanly switch clock inputs. Keep in mind though this testing was just to give you a better understanding and not to characterize the switching time to any sort of guarantee.

I hope this helps. Best,

Will

0 Doug Snook 7 months ago in reply to William Pfennigwerth

Prodigy 10 points

Thanks Will. That is what I need for now. I'll consider this closed with respect to my query. Doug

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LMK00301: Output switching time