12.1.2 Si5391/Si5391P Crystal Guidelines
The following are five recommended crystal guidelines used with external reference devices:
1. Place the crystal as close as possible to the XA/XB pins.
2. DO NOT connect the crystal's GND pins to PCB gnd.
3. Connect the crystal's GND pins to the DUT's X1 and X2 pins via a local crystal GND shield placed around and under the crystal.
See
Figure 12.1 64-pin Si5391/Si5391P Crystal Layout Recommendations Top Layer (Layer 1) on page 52
at the bottom left for an
illustration of how to create a crystal GND shield by placing vias connecting the top layer traces to the shield layer underneath. Note
that a zoom view of the crystal shield layer on the next layer down is shown in
Figure 12.2 Zoom View Crystal Shield Layer, Below the
Top Layer (Layer 2) on page 53
.
4. Minimize traces adjacent to the crystal/oscillator area especially if they are clocks or frequently toggling digital signals.
5. In general do not route GND, power planes/traces, or locate components on the other side, below the crystal GND shield. As an
exception if it is absolutely necessary to use the area on the other side of the board for layout or routing, then place the next reference
plane in the stack-up at least two layers away or at least 0.05 inches away. The Si5391/Si5391P should have all layers underneath the
ground shield removed if possible.
Figure 12.1. 64-pin Si5391/Si5391P Crystal Layout Recommendations Top Layer (Layer 1)
Si5391 Reference Manual • Crystal, XO and Device Circuit Layout Recommendations
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
52
Rev. 0.5 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • January 11, 2022
52