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Associate III
December 18, 2025
Solved

Crystal Capacitor selection verification

  • December 18, 2025
  • 1 reply
  • 357 views

Team,

I have designed Custom Board with STM32F303Rb device and Having USB FS Communication and PWM Compare Output.

I m Using The 8Mhz SMD Crystal (YXC make) : https://www.hxcyic.com/upload/202311/27/202311272250036173.pdf

Datasheet States CL = 20 pF , Cs = 3 pF and ESR = 80 ohm.

From this post : https://community.st.com/t5/stm32-mcus/how-to-select-a-compatible-crystal-and-load-capacitors-for-stm32/ta-p/780236

Deriving Excel Calculation , CL1=CL2 terms out 33pF. Which I populated On Board.

Issue : Sometimes , I am getting Pulse missing Issue during the Run time...Not sure why 

I just want to Verify the CL Value I am using is Corect or Not ?

Previously , I was Using Through hole part HC-49S Crystal with CL1=CL2=20pF.

@mƎALLEm

 

Best answer by mƎALLEm

Hello,

Your calculation is correct:

mALLEm_0-1766049853338.png

But not sure I've understood the issue, so what do you mean by?: 


@bsuthar wrote:

Issue : Sometimes , I am getting Pulse missing Issue during the Run time...Not sure why 


 

1 reply

mƎALLEm
mƎALLEmBest answer
Technical Moderator
December 18, 2025

Hello,

Your calculation is correct:

mALLEm_0-1766049853338.png

But not sure I've understood the issue, so what do you mean by?: 


@bsuthar wrote:

Issue : Sometimes , I am getting Pulse missing Issue during the Run time...Not sure why 


 

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