STM32F103C8 production board schematic

lk.dgironi · ‎2022-01-14

I'm working on a board design with a STM32F103C8. First time for me to build a PCB with STM32, I've always worked with "blue pill" boards.

Not sure about BOOT wiring. The firmware will be uploaded using STM32CubeProgrammer. The board should startup using the internal firmware.

Only HSE External Crystal is used, 8Mhz.

PROG connect is used for programming/debugging.

Can you confirm this design will work? Thanks!

Note: first post here, so excuse me if I'm doing wrong.

lk.dgironi · ‎2022-01-14

Solved.

Schematic attached.

View solution in original post

Peter BENSCH · ‎2022-01-14

Welcome, @Davide G_Oironi, to the community!

C2, C3 seems to be a bit large, check AN2867 for correct values for your crystal
R10 should not be necessary
add a 100nF capacitor between NRST and GND
R9 is also not required

Good luck!

Regards

/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

TDK · ‎2022-01-14

You should have a bulk 4.7uF capacitor on VDD somewhere.

Don't be afraid to use multiple GND and +3V3 symbols on your schematic to increase readability.

If you feel a post has answered your question, please click "Accept as Solution".

lk.dgironi · ‎2022-01-14

Thank you

@Peter BENSCH

1)

According to AN2867 if I'm right I should apply the 3.3 Load Capacitance formula

Supposing Cs 5pF, which I think is a common value for "standard" PCB, my oscillator should have by datasheet 20pF Load Capacitance, so (Cl1*Cl2)/(Cl1+Cl2)=20pF-5pF and Cl1==Cl2 => Cl1,Cl2=30pF

Does it sound right?

2)

Thank's to you I've look at the datasheet, the NRST already has a RPU resistor, so R9 could be removed

3)

done

4)

I've fond R10 in other schematics, never seen that on my AVR experience, I've to investigate why others (in blue pill for example) use this resistor

@TDK

Yes, I've a 10uF on the supply sheet.

You are right, readability is not that much with that few VDD and GND points.

Find schematic updated attached

Peter BENSCH · ‎2022-01-14

The feeback resistor was used in the last century in oscillator circuits that did not have an internal one. However, the STM32s have had this feedback resistor built in since the STM32s era began in 2007.

Why it was used in the Blue Pill... only its developers know.

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

lk.dgironi · ‎2022-01-14

only its developers know :face_with_tears_of_joy: that's right :)

Thank you again.

About the 1) formula, is that right for a 20pF Load Capacitance? By the way the oscillator is a Fundamental one like specified in the AN2867 paper.

Peter BENSCH · ‎2022-01-14

1: yes, 30pF sounds reasonable if CL is actually 20pF (didn't expect a crystal with such a huge load capacitance). 4..5pF for CS are quite common values.

Good luck!

/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

lk.dgironi · ‎2022-01-14

edit:

~ the schematic of this reply is not correct ~

lk.dgironi · ‎2022-01-14

Thank you!

I've posted the updated schematic just in case, for other people.

Peter BENSCH · ‎2022-01-14

Please open the shortcut from NRST to VDD.

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.