SWRA680 November   2020 CC3100 , CC3120 , CC3135 , CC3200 , CC3220R , CC3220S , CC3220SF , CC3235S , CC3235SF

 

  1.   Abstract
  2.   Trademarks
  3. 1Crystal Oscillator Basics
    1. 1.1 Crystal Oscillator Model
  4. 2Crystal Selection
    1. 2.1 Crystal Mode of Operation
    2. 2.2 Temperature Tolerance
    3. 2.3 Aging (Long-Term Stability)
    4. 2.4 Crystal ESR
    5. 2.5 Frequency Accuracy
    6. 2.6 Drive Level
    7. 2.7 Selecting a crystal
      1. 2.7.1 Crystal Specifications
      2. 2.7.2 Recommended Crystals for the CC31xx and CC32xx
  5. 3Crystal Tuning
    1. 3.1 The importance of Crystal Tuning
    2. 3.2 Load Capacitance
    3. 3.3 Crystal Tuning With CL
  6. 4Measuring the ppm Error for the Fast Clock (High Frequency)
    1. 4.1 Setting Up for the CC3x00 Devices
    2. 4.2 Setting Up for the CC3x20 and CC3x35 Devices
    3. 4.3 Measuring ppm Frequency Error
  7. 5PCB Layout Guidelines
    1. 5.1 The 32.768-kHz Crystal (Slow Clock)
    2. 5.2 The 40-MHz Crystal (Fast Clock)
  8. 6References

5.2 The 40-MHz Crystal (Fast Clock)

The 40-MHz Crystal is used to produce the fast clock, which supports the frequency for the WLAN. The crystal requirements for the 32.768-kHz crystal oscillator can be seen in Table 3-1. Below are the PCB gudelines for the slow clock.

The crystal requirements for can be seen in Table 2-2 and Table 2-3.

  • The 40 MHz crystal l should be placed close to the QFN package.
  • Ensure the load capacitance is tuned based on the board parasitic, thus ensuring the frequency tolerance is within ±10 ppm at room temperature, as described in Section 3.
  • The total frequency accuracy for the crystal across parts, temperature, and with aging, should be ±25 ppm to meet the IEEE WLAN standard for 802.11b/g.
  • Ensure no high-frequency lines are routed closer to the crystal routing, to avoid any phase noise degradation.