DocID022913 Rev 2

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AN4067

Conclusion

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Conclusion

Even if internal RC oscillators are factory-calibrated, the user should calibrate them in the

operating environment, when a high-accuracy clock is required in the application.

This application note provides two routines:



High-speed internal oscillator (HSI, HSI14 and HSI48) calibration: how to fine-tune

the oscillator to the typical value.



Low-speed internal oscillator measurement: how to get the “exact” LSI frequency

value.

Several frequency sources can be used to calibrate the internal RC oscillator (HSI): LSE

crystal, AC line, etc. Whatever the reference frequency source, the internal oscillator

calibration principle is the same: a reference signal must be provided to be measured by a

timer. The higher the accuracy of the reference signal frequency, the better the accuracy of

the internal oscillator frequency measurement. The error is computed as the absolute value

of the typical frequency value and the measured one for each trimming value. From this, the

calibration value is calculated and then programmed in the trimming bits.

The second section of this application note is about the measurement of LSI oscillator. The

internal connection between internal oscillators and embedded timers in the STM32F0xx

microcontroller family is used for this purpose. The timer is clocked using the system clock

source and configured in the Input capture mode. The captured time between two

consecutive rising edges of internal oscillator represents an entire period.