SWRA495K December   2015  – April 2024 CC1310 , CC1350 , CC2620 , CC2630 , CC2640 , CC2640R2F , CC2640R2F-Q1 , CC2642R-Q1 , CC2650 , CC2662R-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Oscillator and Crystal Basics
    1. 1.1 Oscillator Operation
    2. 1.2 Quartz Crystal Electrical Model
      1. 1.2.1 Frequency of Oscillation
      2. 1.2.2 Equivalent Series Resistance
      3. 1.2.3 Drive Level
      4. 1.2.4 Crystal Pulling
    3. 1.3 Negative Resistance
    4. 1.4 Time Constant of the Oscillator
  5. 2Overview of Crystal Oscillators for CC devices
    1. 2.1 24-MHz and 48-MHz Crystal Oscillator
    2. 2.2 24-MHz and 48-MHz Crystal Control Loop
    3. 2.3 32.768-kHz Crystal Oscillator
  6. 3Selecting Crystals for the CC devices
    1. 3.1 Mode of Operation
    2. 3.2 Frequency Accuracy
      1. 3.2.1 24-MHz and 48-MHz Crystal
      2. 3.2.2 32.768-kHz Crystal
    3. 3.3 Load Capacitance
    4. 3.4 ESR and Start-Up Time
    5. 3.5 Drive Level and Power Consumption
    6. 3.6 Crystal Package Size
  7. 4PCB Layout of the Crystal
  8. 5Measuring the Amplitude of the Oscillations of Your Crystal
    1. 5.1 Measuring Start-Up Time to Determine HPMRAMP1_TH and XOSC_HF_FAST_START
  9. 6Crystals for CC13xx, CC26xx and CC23xx
  10. 7High Performance BAW Oscillator
  11. 8References
  12. 9Revision History

2.1 24-MHz and 48-MHz Crystal Oscillator

Figure 2-1 shows a simplified block diagram of the XOSC-HF. The oscillator circuit consists of an inverting amplifier, a feedback net, capacitors, and a crystal. The CC devices have an internal capacitor array that can be adjusted and eliminates the requirement for external loading capacitors. The cap-array can be adjusted by the Customer Configuration Flash (CCFG) within a range of 2 pF to 11 pF. For reliable operation, TI requires operating the crystal with CL from 5 to 9 pF. CC13xx/CC26xx Hardware Configuration and PCB Design Considerations shows how to set this value. If no external capacitors are used then the value of CL is determined by the internal loading capacitors plus board parasitic capacitance CP.

GUID-0A83D860-FE1C-46F4-8D6D-FC93B1BF49D3-low.gifFigure 2-1 Simplified Block Diagram of the CC Devices High-Frequency Oscillator With Quartz Crystal

The 24-MHz or 48-MHz crystal is controlled with a control loop described in Section 2.2 and Section 2.3.