The following guidelines are for the slow clock:
- The 32.768kHz crystal must be placed close to the VQFN package.
- Ensure the load capacitance is tuned according to the board parasitics to the frequency tolerance within ±150ppm.
- 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 40MHz crystal must be placed close to the VQFN package.
- Ensure the load capacitance is tuned according to the board parasitics to the frequency tolerance within ±10ppm at room temperature. The total frequency across parts, temperature, and aging must be ±20ppm to meet the WLAN specification.
- To avoid noise degradation, ensure that no high-frequency lines are routed close to the routing of the crystal pins.
- Ensure that crystal tuning capacitors are close to the crystal pads.
- Both traces (XTAL_N and XTAL_P) should be as close as possible to parallel and approximately the same length.
- The ground plane on layer two is solid below the trace lines, and there should be ground around these traces on the top layer.
- For frequency tuning, see CC31xx and CC32xx Frequency Tuning.