The following guidelines are for the slow clock.
- The 32.768-kHz crystal must be placed close to the VQFN package.
- Ensure that the load capacitance is tuned according to the board parasitics to the frequency tolerance is within ±150 ppm.
- The ground plane on layer two is solid below the trace lanes and there is ground around these traces on the top layer.
The following guidelines are for the fast clock.
- The 40-MHz crystal must be placed close to the VQFN package.
- Ensure that he load capacitance is tuned according to the board parasitics to the frequency tolerance is within ±100 ppm at room temperature. The total frequency across parts, temperature, and with aging, must be ±25 ppm to meet the WLAN specification.
- Ensure that no high-frequency lines are routed close to the crystal routing to avoid noise degradation.
- Ensure that crystal tuning capacitors are close to the crystal pads.
- Make both traces (XTAL_N and XTAL_P) as close to parallel as possible and approximately the same length.
- The ground plane on layer two is solid below the trace lines and that there is ground around these traces on the top layer.
- See CC31xx & CC32xx Frequency Tuning for frequency tuning.