2.2 Constraints

The RCOSC_LF calibration is supported for the whole CC13x2/CC26xx temperature range, but care must be taken regarding temperature gradients. To stay within the sleep accuracy requirement of ± 500 ppm, the maximum temperature change per calibration interval cannot be higher than 1°C, with the default calibration interval being 1 second.

The calibration routine will be enabled when selecting RCOSC_LF build configuration as the sleep clock source or modify the project according to the software configuration section (for applications not requiring sleep clock accuracy, the calibration can be manually disabled. For example, non-connectable advertisement used by beacon applications). The calibration will then run automatically every time when the more precise high frequency (24 or 48 MHz) oscillator starts.

To maintain ± 500 ppm accuracy, the calibration must run at least every second assuming the temperature variation does not exceed 1°C per second. In applications with effective Bluetooth Low Energy connection intervals higher than 1 s (time in Standby mode > 1 s), wake-ups must be scheduled at least every second to perform the RCOSC_LF calibration. Similarly, if the application is active for longer time periods than 1 s, the calibration must be triggered by the application. Using the supported build configurations in Section 3.2, the BLE-Stack software will automatically handle these calibration requirements.

NOTE

The 32 kHz crystal-less feature is supported on CC13x2/CC26xx wireless MCUs implementing the Bluetooth Low Energy peripheral, observer and broadcast (beacon) roles only. Thus, all central role or master devices must use the 32 kHz crystal oscillator.