DocID022913 Rev 2

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AN4067

Internal RC oscillator calibration

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3.5

Calibration process performance

3.5.1

Duration of the calibration process

The duration of the calibration process depends on:

1.

2.

3.

the number of measured frequencies during the calibration process “number of steps”.

Once the peripherals are configured and ready (mainly the LSE oscillator), the duration of

the calibration process is approximated by:

If the calibration process is run with a minimum frequency error for an HSI oscillator

(HSI_CalibrateMinError()), the number of steps is equal to 32. If the LSE oscillator is

prescaler = 32768/8 = 4096 Hz) and the selected number of measured periods is 10, the

calibration consumes approximately:

duration = (2 x 51 x 32) / 4096 = 797 ms

The duration of the calibration process with a maximum allowed error is lower than or equal

to the duration of calibration when using the minimum frequency error process.

Note:

Multiplying by 2 in the duration formula above is due to the fact that there is no

synchronization between the reference signal and the start of counting by the timer.