Si5345-44-42-D-RM
Rev. 1.0
73
12.2. 44-Pin QFN Si5344/42 Layout Recommendations
This section details the layout recommendations for the 44-pin Si5344 and Si5342 devices using an example 6-
layer PCB.
The following guidelines details images of a six layer board with the following stack:
Layer 1: device layer, with low speed CMOS control/status signals, ground flooded
Layer 2: crystal shield, output clocks, ground flooded
Layer 3: ground plane
Layer 4: power distribution, ground flooded
Layer 5: input clocks, ground flooded
Layer 6: low-speed CMOS control/status signals, ground flooded
This layout was designed to implement either a crystal or an external oscillator as the XAXB reference. The top
layer is flooded with ground. The clock output pins go to layer 2 using vias to avoid crosstalk during transit. When
the clock output signals are on layer 2 there is a ground shield above, below and on all sides for protection. Output
clocks should always be routed on an internal layer with ground reference planes directly above and below. The
plane that has the routing for the output clocks should have ground flooded near the clock traces to further isolate
the clocks from noise and other signals.
12.2.1. Si5342/44 Applications without a Crystal
If the application does not use a crystal, then the X1 and X2 pins should be left as “no connect” and should not be
tied to ground. In addition, there is no need for a crystal shield or the voids underneath the shield. If there is a
differential external clock input on XAXB there should be a termination circuit near the XA and XB pins. This
termination circuit should be two 50
resistors and one 0.1 µF cap connected in the same manner as on the other
clock inputs (IN0, IN1 and IN2). The clock input on XAXB must be ac-coupled. Care should be taken to keep all
clock inputs well isolated from each other as well as any other dynamic signal.
Figure 48. Device Layer (Layer 1)