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Posts: 3
Registered: ‎11-28-2014

What behaviour will I see in the output clock when changing Frequency Select Si552

I am using a SiliconLabs 552FC000270DG VXCO with Frequency Select capability.  I am wondering exactly what sort of behaviour should I expect in the output clock when I change from one frequency to another?

 

Thanks and best regards,

 

Scott Bezan

Posts: 3
Registered: ‎11-28-2014

Re: What behaviour will I see in the output clock when changing Frequency Select Si552

Perhaps I should augment my question with: this is actually what I'm seeing:

 

pal_04fw_hdsdiclk_hdvxcofs1_failed.jpg

Posts: 19
Registered: ‎11-21-2014

Re: What behaviour will I see in the output clock when changing Frequency Select Si552

Hi Scott,

 

When using the Frequency Select option, there will be a maximum of 10ms of settling time after a Frequency Select change has been made. During this time, the part will stop outputting until the new frequency has been calibrated and then begin outputting at the new frequency once this calibration has been completed. The waveform you posted is the expected behavior when using the Frequency Select option. During the calibration step, there is a chance glitches may occur momentarily affecting the output. The 10ms settling time guarantees a stable output at the new frequency after the Frequency Select change.

 

Regards,

Matt

<a href="http://community.silabs.com/t5/Welcome-and-Announcements/Community-Ranking-System-and-Recognition-Program/m-p/140490#U140490"><font color="#000000"><font size="2">Hero</font></font> </a> jmg
Posts: 1,136
Registered: ‎04-27-2004

Re: What behaviour will I see in the output clock when changing Frequency Select Si552


maklug wrote:

When using the Frequency Select option, there will be a maximum of 10ms of settling time after a Frequency Select change has been made.

 


Does that 10ms also depend on the size of the change ?

The scope plot seems to be a lot faster than that 10ms worst case - shows 196us release time delay, and ~ 225us quiet time before the new frequency is enabled on the output.

 

 

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Posts: 3
Registered: ‎11-28-2014

Re: What behaviour will I see in the output clock when changing Frequency Select Si552

Thank you Matt for your reply.  I just wanted to make sure what I was seeing was in fact valid.

 

Best regards,

 

Scott