AN4631 datasheet(22/30 Pages) STMICROELECTRONICS

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Internal RC oscillator calibration

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DocID027266 Rev 2

2.5

Calibration process performance

2.5.1

Duration of the calibration process

The duration of the calibration process depends on:

the frequency of the reference signal (prescaled value) “REFERENCE_FREQUENCY”,

the number of measured periods per trimming value “NUMBER_OF_LOOPS”,

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:

duration = (2 x (NUMBER_OF_LOOPS + 1) x number of steps) / REFERENCE_FREQUENCY

If the calibration process is run with a minimum frequency error for HSI16 oscillator

(HSI16_CalibrateMinError()), the number of steps is equal to 32. If the LSE oscillator

is used as the reference frequency (REFERENCE_FREQUENCY = LSE value / Input capture

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

calibration consumes approximately:

duration = (2 x 11 x 32) / 4096 = 172 ms

AN4631 Datasheet(PDF) 22 Page - STMicroelectronics