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

2.7 Selecting a crystal

This section presents some important considerations when selecting crystals for the CC31xx and CC32xx. Selecting a crystal for a specific application will depend on the following three factors:

  • Size (footprint area and height)
  • Performance (accuracy over temperature, lifetime, power consumption, and start-up time)
  • Cost

Consider the following when selecting a crystal:

  • Crystals must be selected to meet requirements listed in the CC31xx and CC32xx data sheets or specifications.
    • ESR must not be greater than can be driven by CC31xx and CC32xx.
    • Capacitive loading (CL) and frequency tolerance (ppm) must meet the specifications of the standard used (for example, Wi-Fi®).
  • Some other considerations when selecting a crystal include the following:
    • To improve start-up time and reduce power consumption, the crystal must have the following:
      • Low-capacitive loading, at the expense of greater susceptibility to frequency variation caused by the environment (CL)
      • Low-motional inductance (LM)
      • Low-motional resistance (RM)