SWRA495L December   2015  – April 2025 CC1310 , CC1350 , CC2620 , CC2630 , CC2640 , CC2640R2F , CC2640R2F-Q1 , CC2642R-Q1 , CC2650 , CC2662R-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Oscillator 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. 2 Overview of Crystal Oscillators for CC devices
    1. 2.1 24MHz and 48MHz Crystal Oscillator
    2. 2.2 24MHz and 48MHz Crystal Control Loop
    3. 2.3 32.768kHz Crystal Oscillator
  6. 3 Selecting Crystals for the CC devices
    1. 3.1 Mode of Operation
    2. 3.2 Frequency Accuracy
      1. 3.2.1 24MHz and 48MHz Crystal
      2. 3.2.2 32.768kHz 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. 4 PCB Layout of the Crystal
  8. 5 Measuring 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. 6 Crystals for CC13xx, CC26xx, CC23xx and CC27xx
  10. 7 High Performance BAW Oscillator
  11. 8 CC23XX and CC27XX Software Amplitude Compensation
  12. 9 Internal Capacitor Array for CC23XX and CC27XX
  13. 10Internal Capacitor Array for CC13xx and CC26xx
  14. 11Summary
  15. 12References
  16. 13Revision History

Abstract

The CC13xx, CC26xx, CC23xx, and CC27xx family are low-power wireless microcontrollers (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, CC23xx, and CC27xx family devices, unless otherwise noted. The generic term CC devices is used for simplification. The CC devices have integrated 24MHz (CC13x0 and CC26x0) or 48MHz (CC13x2, CC26x2, CC23xx, CC27xx) and 32.768kHz crystal oscillators TI designed for use with low-cost quartz crystals. The 24MHz and 48MHz oscillator (XOSC-HF for CC13xx and CC26xx; HFXT for CC23xx and CC27xx) 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 32kHz crystal oscillator (XOSC-LF for CC13xx and CC26xx; LFXT for CC23xx and CC27xx) 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.