LMK04803: LOS function details

Jayden Qiu

Part Number: LMK04803

Tool/software:

Hi team,

This is FAE Jayden, my customer is using LMK04803BISQX, and they have some questions that need to reach out to you.

1) As described in datasheet, Pin 62 and Pin 63 can be configured as LOS status indictor. Device pin 62/63, Status_CLKin1, can be used as LOS status monitoring.

Regarding the detection principle of loss of signal, or the detection window, can you help clarify under what specific conditions will the input signal be judged as lost? Are there clear indicator requirements for the amplitude, frequency deviation, and duration of signal loss of the input signal?
Regarding the signal amplitude, the datasheet currently gives the minimum differential input signal of 0.5Vpp. When the amplitude is less than what, an alarm will be reported?

2) As for handover mode, If the input signal is lost, the output signal will be locked to the state before the signal was lost. Do we have corresponding data on the performance of long-term operation in this state? If it is kept in holdover mode for a long time, can the signal quality of the output signal be maintained? Will the output signal amplitude, frequency deviation and other indicators change over time? If the input signal does not appear again, will the holdover mode be maintained?

Brs

Jayden

over 1 year ago

0 William Pfennigwerth over 1 year ago

TI__Expert 8421 points

Hello,

I apologize for the delay. I will get back to you tomorrow.

Regards,

Will

0 Jayden Qiu over 1 year ago in reply to William Pfennigwerth

TI__Intellectual 1405 points

Hi William,

Thanks, look forward to your reply.

Jayden

0 William Pfennigwerth over 1 year ago in reply to Jayden Qiu

TI__Expert 8421 points

Jayden,

Other than the timing listed in the datasheet, I am not sure about the input requirements for triggering LOS. I can ask our design team and follow up.

In regards to holdover performance. Section 8.3.5.5 gives a good overview of the frequency stability. In regards to the amplitude there should be no change as the VCO/VCXO tuning voltage is the only thing being adjusted. Holdover mode can be maintained indefinitely, although I do not have any long term data to support the signal performance.

Regards,

Will

0 Jayden Qiu over 1 year ago in reply to William Pfennigwerth

TI__Intellectual 1405 points

hi will，

Many thanks. Any feedback for the first question？

Brs

Jayden

0 William Pfennigwerth over 1 year ago in reply to Jayden Qiu

TI__Expert 8421 points

Jayden,

After doing some tests in the lab, it looks like LOS is triggered when when the signal is under 80mV. There is no mechanism for frequency deviation as that is not a "Loss-of-Signal" but will instead unlock the PLL which can be alarmed with the Digital Lock Detect functionality. So LOS will be triggered whenever there is a signal with <80mV of amplitude present at CLKIn representative of a true signal loss.

Regards,

Will

Clock & timing

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LMK04803: LOS function details