February 2015

DocID022913 Rev 2

1/27

1

AN4067

Application note

Calibrating STM32F0x1, STM32F0x2 and STM32F0x8 lines

internal RC oscillators

Introduction

Microcontrollers of STM32F0x1, STM32F0x2 and STM32F0x8 product lines, named

STM32F0xx in this document, have internalRC oscillators that can be selected as the

system clock source, and a High speed internal RC oscillator dedicated to ADC. These are

known as the HSI (High-speed Internal 8 MHz), HSI14 (High-speed Internal 14 MHz) and

HSI48 (High-speed Internal 48 MHz) oscillators.

The operating temperature has an impact on the accuracy of the RC oscillators. At 25 °C,

the HSI, HSI14 and HSI48 oscillators have an accuracy of ±1% typically, but in the

temperature range of -40 to 105 °C, the accuracy decreases.

To compensate for the influence of temperature on internal RC oscillators accuracy, the

STM32F0xx microcontrollers have built-in features to allow users to calibrate the HSI and

HSI14 oscillators and measure the LSI (Low-speed internal) oscillator frequency.

This application note focuses on how to calibrate internal RC oscillators: HSI, HSI14 and

HSI48. Three methods are presented:



Method 1 consists in finding the frequency with the minimum error.



Method 2 consists in finding the maximum allowed frequency error.



Method 3 consists in preparing the table of calibration values that is later used for fast

calibration.

All three methods are implemented by providing an accurate reference signal.

The measurement of the LSI oscillator is performed by connecting the oscillator to a timer

input capture.

Table 1 lists the microcontrollers and software concerned by this application note.

Table 1. Applicable products and software

Type

Part number and product line

Microcontrollers

STM32F0x1 line, STM32F0x2 line and STM32F0x8 line.

Software

STSW-STM32132

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