This application report explains how you can configure the Bluetooth Low Energy (BLE) software stack to operate without the need for a 32 kHz crystal on the SimpleLink™ CC13x2 and CC26xx devices.
This application report explains how to configure this mode of operation, what considerations have to be taken to use the internal RC low frequency oscillator (RCOSC_LF) for the Bluetooth Low Energy peripheral and broadcast (beacon) role devices instead of the 32 kHz crystal, and what impact it has on current consumption. This document assumes the reader is familiar with the concepts described in the BLE5-Stack Users Guide and the CC13x2, CC26x2 SimplinkTM Wireless MCU Technical Reference Manual.
Removing the 32 kHz crystal from a design decreases the required board space, reduces the bill of material (BOM) costand simplifies procurement.
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The Bluetooth specification puts a strict requirement on the accuracy of the sleep clocks for Bluetooth Low Energy devices that are intended to enter (and stay) in a connection. The specification requires that devices have a sleep clock accuracy (SCA) that meets ± 500 ppm. For more details on the SCA requirement, see the Sleep Clock Accuracy section in the Bluetooth core specification 4.0, Volume 6. that can be downloaded from the following URL: https://www.bluetooth.com/specifications/adopted-specifications.
This sleep clock accuracy (SCA) requirement is valid for both the master and slave side of the Bluetooth Low Energy connection; however, devices such as Bluetoooth Low Energy beacons do not require such accuracy as the advertising interval is intentionally varied to prevent collisions. The intention of the SCA requirement is to ensure low power consumption while maintaining flexibility in the component selection. The amount of time a slave device must stay in active RX mode, referred to as the receive window, is dependent upon the sleep clock tolerance; a less accurate sleep clock requires the receive window time to be increased, thus, increasing the average current consumption.