ZHCU623 January   2019

 

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4.3.1 Layout Considerations for the CC2640R2F

The CC2640R2F, along with the RF matching network and antenna, will require a large copper pour on the bottom layer of the board to provide a low impedance path to ground. In a two-layer design, this means that only the top layer is available to route signals to and from the CC2640R2F. Take care to ensure that the necessary bypass components are still placed as close to the IC as possible. Multiple vias underneath the CC2640R2F provide a low impedance path to ground for the device itself. Figure 26 shows the CC2640R2F footprint and wiring on the flex PCB.

Remember to consider the width of the signal traces to the balun and RF antenna in two-layer design cases. With the most rigid PCBs, it is often possible to find reasonable width traces that provide matching to design impedances. In the case of a 2-layer design, the thickness of the board, the PCB design rules, and the desired cost of the boards will limit the maximum characteristic impedance of these traces. If matching is not possible, TI recommends to keep these traces as short as possible. Additionally, a pi-type matching network using 0201 footprints was left to allow matching with lumped elements. RF Impedance matching should be performed with the patch adhered to a wearer's skin to emulate the environment of use.

TIDA-01624 CC2640R2F_Layout_Rotated.pngFigure 26. CC2640R2F Routing on 2-Layer Flex Patch With Ground Plane Shown in Blue