Importance of Rext Resistor in STM32 external Crystal Oscillator

[Savan_Sutariya]

Hello ST community,

I'm currently working on a circuit utilizing an ATS240C-E Crystal with a 22pF capacitor for an STM32 microcontroller. I'm curious about the necessity and implications of including a Rext resistor in the output of the crystal oscillator. Could anyone shed light on whether the Rext resistor is necessary for STM32 microcontrollers? Furthermore, I'd like to understand how its presence or absence affects the performance, stability, and functionality of the oscillator, particularly in noisy and EMI conditions.

If anyone has insights or experiences to share regarding this matter, I would greatly appreciate it.

Thank you in advance for your assistance.

[mƎALLEm]

Hello,

Refer to the AN2867 "Guidelines for oscillator design on STM8AF/AL/S, and STM32 MCUs/MPUs"

Specifically the section: 3.5 Drive level and external resistor calculation / 3.5.3 Calculating the external resistor.

Hope it does answer your question.