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

Abstract

The CC13xx, CC26xx, and CC23xx family are low-power wireless MCU platforms supporting multiple standards (that is, Bluetooth® low energy, IEEE® 802.15.4, and proprietary RF protocols). The document is valid for all CC13xx, CC26xx and CC23xx family devices, unless otherwise noted. The generic term "CC devices" is used for simplification. The CC devices have integrated 24-MHz (CC13x0 and CC26x0) or 48-MHz (CC13x2, CC26x2, CC23xx) and 32.768-kHz crystal oscillators TI designed for use with low-cost quartz crystals. The 24/48-MHz oscillator (XOSC-HF) generates the reference clock for the RF blocks and the MCU system. RF systems are dependent on accurate clocks for correct operation. A deviation in clock frequency is reflected as a deviation in radio frequency. This deviation can degrade RF performance, violate regulatory requirements, or lead to a nonfunctioning system. In power-down mode, the high-frequency oscillator is typically turned off and a low-frequency oscillator is the system clock. For time-synchronized protocols such as Bluetooth low energy, a tight tolerance on the sleep clock enables longer time in low-power mode and reduced power consumption important in battery-powered applications. For this low-frequency oscillator, typically a 32-kHz crystal oscillator (XOSC-LF) is used.

The scope of this application report is to discuss the requirements and trade-offs of the crystal oscillators for this CC devices and provide information on how to select an appropriate crystal. This document also presents steps to configure the device to operate with a given crystal. You must configure the CC devices based on the crystal used (that is, adjust the internal capacitor array to match the loading capacitor of the crystal for the XOSC-HF). This application report also discusses some measurement approaches that can be used to characterize certain performance metrics, including crystal oscillator amplitude, and start-up time.