STM32F407VGT6 external oscillator

[kemalerdinctuncer]

Posted on July 19, 2016 at 13:19

Hi everyone,

I have designed a board using stm32f407vgt6 and placed a 8MHz crystal oscillator with 22pF capacitors. The code I wrote works perfectly with stm32f4discovery. But when I try to use my board, it can't initialize external oscillator and use 16 MHz internal oscillator. I can't find the problem and want to know if it may be about pcb design or the components. Thanks in advance. #external-clock #hse #stm32f4-oscillator

[waclawek.jan]

Posted on July 19, 2016 at 13:51

> 8MHz crystal oscillator with 22pF capacitors

Crystal, or a crystal oscillator? Crystal oscillator has at least 4 pins and wouldn't need capacitors, but would need a supply connected. But I assume you have a 2-pin crystal. Not all crystals are created equal, and 22pF may be not adequate. Also, the layout may be critical, it's a low-power high-frequency circuit, basically of analogue nature. Read AN2867: Oscillator design guide for STM8S, STM8A and STM32 microcontrollers. JW

[kemalerdinctuncer]

Posted on July 19, 2016 at 14:08

Sorry, it is a crystal, can capacitors alone cause this? Because it acts like there is no crystal.

[Nesrine M_O]

Posted on July 19, 2016 at 15:06

Hi tuncer.erdinc,

I recommend you to have a look to the

http://www.st.com/content/ccc/resource/technical/document/application_note/76/f9/c8/10/8a/33/4b/f0/DM00115714.pdf/files/DM00115714.pdf/jcr:content/translations/en.DM00115714.pdf

application note it may be helpful. -Syrine-