AN2867 Datasheet, PDF (1/41 Pages) STMicroelectronics – Oscillator design guide for STM8S

AN2867
Application note
Oscillator design guide for STM8S, STM8A
and STM32 microcontrollers
Introduction
Most designers are familiar with oscillators (Pierce-Gate topology), but few really
understand how they operate, let alone how to properly design an oscillator. In practice,
most designers do not even really pay attention to the oscillator design until they realize the
oscillator does not operate properly (usually when it is already being produced). This should
not happen. Many systems or projects are delayed in their deployment because of a crystal
not working as intended. The oscillator should receive its proper amount of attention during
the design phase, well before the manufacturing phase. The designer would then avoid the
nightmare scenario of products being returned.
This application note introduces the Pierce oscillator basics and provides some guidelines
for a good oscillator design. It also shows how to determine the different external
components and provides guidelines for a good PCB for the oscillator.
This document finally contains an easy guideline to select suitable crystals and external
components, and it lists some recommended crystals (HSE and LSE) for STM32 and
STM8A/S microcontrollers in order to quick start development. Refer to Table 1 for the list of
applicable products.
Table 1. Applicable products
Type
Product categories
STM8S Series
Microcontrollers
STM8AF Series, STM8AL Series
STM32 32-bit ARM Cortex MCUs.
February 2015
DocID15287 Rev 9
1/41
www.st.com
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