Silicon Laboratories SI5375 - Manual (Page 110)

S i 5 3 x x - R M
110 Rev. 1.2
In some applications, a crystal with frequencies other than 114.285 MHz may be used. See “AN591: Crystal
Selection for the Si5315, Si5317, and other Si53xx Any-Frequency Jitter Attenuating Clocks” for details and a
current list of crystal vendors and approved part numbers.
External reference (and crystal) frequency values should be avoided that result in an output frequency that is an
integer or near integer multiple of the reference frequency. See Appendix B on page 112 for details.
Because the crystal is used as a jitter reference, rapid changes of the crystal temperature can temporarily disturb
the output phase and frequency. For example, it is recommended that the crystal not be placed close to a fan that
is being turned off and on. If a situation such as this is unavoidable, the crystal should be thermally isolated with an
insulating cover.
Fundamental Mode Crystals
For cost sensitive applications that do not have the most demanding jitter requirements, all of the narrow band
devices can use fundamental mode crystals that are in the lowest frequency band ranging from 37 to 41 MHz
(corresponding to RATE = LL). Unlike the other narrowband members of the family, the Si5327 is only capable of
using fundamental mode crystals that are in this range. For a more detailed discussion of the trade-offs associated
with this approach and a list of approved low frequency crystals, please see the application note AN591, which can
be downloaded from
www.silabs.com/timing .
Table 51. XA/XB Reference Sources and Frequencies
RATE[1:0] NB/WB Type Recommended Lower limit Upper limit
HH WB No crystal or external clock — — —
HM NB Reserved — — —
HL NB Reserved — — —
MH NB External clock 114.285 MHz 109 MHz 125.5 MHz
MM NB Third overtone crystal 114.285 MHz — —
ML NB External clock 57.1425 MHz 55 MHz 61 MHz
LH NB Reserved — — —
LM NB External clock 38.88 MHz 37 MHz 41 MHz
LL NB Fundamental mode crystal 40 MHz 37 MHz 41 MHz