7.2 Types of Inputs
7.2.1 Crystal on XA/XB
An external standard crystal (XTAL) is connected to XA/XB when this input is configured as a crystal oscillator. For all Si5391 devices,
except the Si5391P, a crystal frequency of 25 MHz can be used, although crystals in the frequency range of 48 MHz to 54 MHz are
highly recommended for the best jitter performance. All Si5391 devices, except Si5391P, include a built-in XTAL load capacitance (C
L
)
of 8 pF, but crystals with CL specifications as high as 18 pF can also be used. When using crystals with CL specs higher than 8 pf it
is not generally recommended to use external capacitors from XA/XB to ground to increase the crystal load capacitance. See Section
12. Crystal, XO and Device Circuit Layout Recommendations
for the PCB layout guidelines.
For Si5391P devices, the crystal frequency MUST be 48 MHz and have a loading capacitance of 8 pf. No external loading capacitors
are needed since the device has a built-in loading capacitance of 8 pf.
Si5391 Reference Manual • Clock Inputs
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Rev. 0.5 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • January 11, 2022
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