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

3.4 ESR and Start-Up Time

ESR (equivalent series resistance) is a parameter of the crystal in the data sheet of the crystal. Negative resistance is a parameter of the complete oscillator circuit, including capacitor values, crystal parameters, and an on-chip circuit. To ensure best start-up of the crystal oscillator, the negative resistance magnitude must be at least 3 times greater than RN (see Equation 10 and Equation 11) during initial start up.

Equation 10. GUID-0DD8A2DA-E0A6-4173-A4BA-2CE47EB441C3-low.gif
Equation 11. GUID-88D1B83D-9FDF-4794-B2C4-7C5C5565FE69-low.gif

If the negative resistance magnitude is not 3× greater than ESR during initial start-up, the oscillator might not operate optimally or might fail to start in the presence of environmental changes or manufacturing variations in the crystal.

Note: Crystals with higher ESR typically result in longer start-up times than crystals with lower ESR. A higher-load capacitance decreases the negative resistance of the oscillator and increases the start-up time.