SI5327 Datasheet, PDF (20/60 Pages) Silicon Laboratories – ANY-FREQUENCY PRECISION CLOCK MULTIPLIER/JITTER ATTENUATOR

Si5327
4.1. External Reference
An external, high quality clock or a low-cost 40 MHz
crystal is used as part of a fixed-frequency oscillator
within the DSPLL. This external reference is required for
the device to perform jitter attenuation. Silicon
Laboratories recommends using a high quality crystal.
Specific recommendations may be found in the Family
Reference Manual.
In digital hold, the DSPLL remains locked and tracks the
external reference. Note that crystals can have
temperature sensitivities.
If there is a need to use a reference oscillator instead of
a crystal, Silicon Labs does not recommend using
MEMS based oscillators. The very low loop BW of the
Si5327 means that it can be susceptible to XAXB
reference sources that have high wander. Experience
has shown that in spite of having low jitter, some MEMs
oscillators have high wander, and these devices should
be avoided. Contact Silicon Labs for details.
4.2. Further Documentation
Consult the Silicon Laboratories Si53xx Any Frequency
Precision Clock Family Reference Manual (Si53xx
FRM) for detailed information about the Si5327
functions. Additional design support is available from
Silicon Laboratories through your distributor.
Silicon Laboratories has developed a PC-based
software utility called DSPLLsim to simplify device
configuration, including frequency planning and loop
bandwidth selection. The FRM and this utility can be
downloaded from http://www.silabs.com/timing.
Table 8. CKOUT_ALWAYS_ON and SQ_ICAL Truth Table
CKOUT_ALWAYS_ON
0
0
1
1
SQ_ICAL
0
1
0
1
Results
CKOUT OFF until after the first ICAL
CKOUT OFF until after the first successful
ICAL (i.e., when LOL is low)
CKOUT always ON, including during an ICAL
CKOUT always ON, including during an ICAL.
Use these settings to preserve output-to-output
skew
20
Rev. 1.0