si5315 Silicon Laboratories, si5315 Datasheet - Page 43

• Manufacturer Part Number: si5315
• Description: Synchronous Ethernet/telecom Jitter Attenuating Clock Multiplier
• Manufacturer: Silicon Laboratories

6.1. Crystal/Reference Clock Selection
An external 40 MHz clock or a low-cost 40 MHz fundamental mode 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.
In holdover, the DSPLL remains locked to this external reference. Any changes in the frequency of this reference
when the DSPLL is in holdover will be tracked by the output of the device. Note that crystals can have temperature
sensitivities. Table 16 shows the recommended 40 MHz fundamental mode crystals.
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.
6.1.1. Reference Drift
During holdover, long-term and temperature related drift of the reference input result in a one-to-one drift of the
output frequency. That is, the stability of the any-rate output is identical to the drift of the reference frequency. This
means that for the most demanding applications where the drift of a crystal is not acceptable, an external
temperature compensated or ovenized oscillator will be required. Drift is not an issue unless the part is in holdover.
Also, the initial accuracy of the reference oscillator (or crystal) is not relevant.
6.1.2. Reference Jitter
Jitter on the reference input has a roughly one-to-one transfer function to the output jitter over the bandwidth
ranging from 100 Hz up to 30 kHz. If a crystal is used on the XA/XB pins, the reference will have low jitter if a
suitable crystal is in use. If the XA/XB pins are connected to an external reference oscillator, the jitter of the
external reference oscillator may contribute significantly to the output jitter.
Note: While these crystals meet the preceding criteria according to their data sheets, Silicon
ECS Inc., International
Abracon Corporation
CTS Corporation
Connor Winfield
Manufacturer
Laboratories, Inc. does not guarantee operation with the Si5315, nor does Silicon Laboratories
endorse one supplier of crystals over another. Contact Silicon Labs for details and a current list
of crystal vendors and recommended part numbers.
Mtron
XTAL/CLOCK
Table 17. XA/XB Reference Sources
Table 16. Recommended Crystals
M1253-3-P-P-40.0000MHz
ECS-400-20-33-A-S-L-TR
ABM8-40.000MHZ-B2-T
M
L
Part Number
Preliminary Rev. 0.2
XL-1CE
403
40 MHz crystal
External clock
Type
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http://www.conwin.com
http://ctscorp.com
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http://ecsxtal.com
Web Site
Si5315
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