9. XO and Device Circuit Layout Recommendations
The main layout issues that should be carefully considered for optimum phase noise include the following:
• Number and size of the ground/thermal vias for the Epad (see
)
• Output clock trace routing
• Input clock trace routing
• Control and Status signals to input or output clock trace coupling
Si5386A-E-EVB schematics, layouts, and component BOM files are available at:
https://www.skyworksinc.com/en/products/timing/eval-
uation-kits/jitter-attenuator/si5386-evaluation-kit
9.1 Si5386 64-Pin QFN External XO Layout Recommendations
This section details the recommended guidelines for the layout of the 64-pin QFN Si5386 with external XO using the 8-layer Si5386A-E-
EB PCB. The following are the descriptions of each of the eight layers.
• Layer 1: device layer, with low speed CMOS control/status signals, ground flooded
• Layer 2: input clocks, ground flooded
• Layer 3: ground plane
• Layer 4: power distribution, ground flooded
• Layer 5: power routing layer
• Layer 6: ground input clocks, ground flooded
• Layer 7: output clocks layer
• Layer 8: ground layer
External XO: The figure below shows the top layer layout of the Si5386 device mounted on the PCB. The XO is outlined with the white
box around it. The top layer is flooded with ground. Both the XA and XB pins are capacitively coupled, with XB ac connected to XO
ground for single-ended output XO's. Notice the 5x5 array of thermal vias in the center of the device. See
information on thermal/ground via layout.
Figure 9.1. External XO: Si5386 Device and XO Layout Recommendations, Top Layer (Layer 1)
Si5386 Rev. E Reference Manual • XO and Device Circuit Layout Recommendations
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Rev. 1.2 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • December 9, 2021
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