4. Clock Inputs
The PLL in the Si5341/40 requires a clock at the XAXB or IN2, 1, 0 input pins or a clock from a crystal connected across the XAXB
pins.
4.1 Inputs on XA/XB
4.1.1 Crystal on XA/XB
An external standard crystal (XTAL) is connected to XA/XB when this input is configured as a crystal oscillator. A crystal frequency of
25 MHz can be used although crystals in the frequency range of 48 MHz to 54 MHz are recommended for the best jitter performance.
Recommended crystals are listed below. The Si5341/40 includes 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. Rather the frequency offset due to C
L
mismatch can be adjusted using the XAXB_FREQ_OFFSET word which allows frequency adjustments of up to ±1000 ppm. See
11. Crystal and Device Circuit Layout Recommendations
for the PCB layout guidelines.
Si5341, Si5340 Rev D Family Reference Manual • Clock Inputs
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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Rev. 1.3 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • July 26, 2021
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