Meaning
Integrated clock sources that operate at low frequencies provide the timing reference for power-saving sleep modes in microcontrollers. The use of an LFRCO (low-frequency RC oscillator) allows the device to disable its high-frequency crystal oscillator while maintaining a source for the real-time clock and watchdog timer. This component is integrated directly onto the silicon die to eliminate the need for an external crystal.
Current Consumption
The primary benefit of this oscillator is its extremely low operating current, which is typically in the nanoampere range. This low draw is achieved by using a simple internal circuit that does not require the high power needed to drive a quartz crystal.
Frequency Drift
The accuracy of this internal clock source is relatively low and varies significantly with changes in temperature and supply voltage. Without periodic calibration, the accumulated timing error can cause the device to miss scheduled communication windows.
Calibration Routine
The system can compensate for this drift by periodically comparing the low-frequency clock against the high-frequency crystal oscillator. This comparison is performed when the high-frequency clock is active during a radio transmission or data processing task. The calculated offset is used to adjust the sleep interval counters in the firmware.
This dynamic calibration maintains sufficient timing accuracy while keeping the average power consumption of the device extremely low.
