Silicon Laboratories SI5322 User Manual

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All crystals and external oscillators must lie within these two bands

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Not every crystal will work; they should be tested

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An external oscillator can be used at all four bands

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The frequency at the phase detector (f3) must be the same for both CKIN1 and XA/XB or else switching cannot 
be hitless 

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To avoid spurs, avoid outputs that are an integer (or near integer) of the XA/XB frequency.

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While in Free Run:

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CKOUT frequency tracks the reference frequency.

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 For very low drift, a TCXO or OCXO reference is necessary.

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CKOUT Jitter:

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XA/XB to CKOUT jitter transfer function is roughly one-to-one.

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For very low jitter, either use a high quality crystal or external oscillator.

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 3rd overtone crystals have lower close-in phase noise.

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In general, higher XA/XB frequency > lower jitter.

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XA/XB frequency accuracy:

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For hitless switching, to meet all published specifications, the XA/XB frequency divided by N32 should match the CLKIN 

frequency divided by N31. If they do not match, the clock switch will still be well-behaved.

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Other than the above, the absolute accuracy of the 

XA/XB

 frequency is not important.

109 MHz

125.5 MHz

3rd overtone

37 MHz

41 MHz

Fundamental

CKIN

N31

---------------

XA-XB

N32

------------------

f

3

=

=

CKOUT

XA-XB

----------------------

Integer

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