This application note introduces the Pierce oscillator basics and provides some guidelines for a good oscillator design, including selecting suitable crystals and external components, and designing a good PCB for the oscillator.
The document introduces the basics of Pierce oscillators and offers practical design guidelines, including component selection and PCB layout tips. It also presents methods to calculate drive level, startup time, and crystal pullability.
Sections cover quartz crystal properties, oscillator theory, detailed Pierce oscillator circuitry, a step‑by‑step crystal selection guide, recommended HSE/LSE crystals for STM32 devices, PCB layout recommendations, and a concluding summary.
| Motional inductance (Lin) | 14.7 mH |
|---|---|
| Motional capacitance (Cn) | 0.027 pF |
| Shunt capacitance (Co) | 5.57 pF |
A load capacitance of 4.02 pF will make the crystal oscillate at exactly 8 MHz.
Section 6 lists recommended HSE and LSE crystals for STM32™ microcontrollers.
Typical feedback resistor values are given in the note for various frequencies.