This article introduces the ST microcontroller oscillator circuit design guide, including the principles of oscillators, design of Pierce oscillators, characteristics and models of quartz oscillators, etc.
This application note introduces the basic theory of Pierce crystal oscillators and provides practical design guidance. It covers oscillator principle, gain margin, feedback resistor selection, load capacitance calculation, and driving level considerations.
The document also offers a quick selection guide for crystals and external components, lists recommended crystal and ceramic oscillator models for STM32 HSE and LSE sections, and gives PCB layout recommendations to ensure reliable start‑up and stable operation. This manual is written in Chinese.
| Feedback resistor RF range (32.768 kHz) | 10 to 25 MΩ |
|---|---|
| External resistor RExt for 8 MHz crystal with CL2 = 15 pF | ≈ 1326 Ω |
Use the crystal’s load capacitance (CL2) to compute its reactance; for CL2 = 15 pF the calculated RExt is about 1326 Ω.
A feedback resistor between 10 MΩ and 25 MΩ is recommended for 32.768 kHz crystals.