Noise when pwm to H-bridge

[DavidVestergaard]

Hi

I am working on a custom PCB board featuring a stm32 and a H-bridge to drive a DC motor. I am facing some noise only when i pwm (16KHz). I can also measure the noise on the other pins of the MCU. I have added a scope picture and the circuit. Any comments is very appreciated!

I found out the caps C3 and C4 made a lot of instability, so they are NOT mounted.

Friendly regards, David

 

[KlausST]

Hi,

you could have the same schematic with two different PCB layouts.
The one circuit may work properly while the other causes problems.

The PCB of switching power circuits is always critical, thus usually the manufacturere provides informations (PCB guidelines) to ensure proper operation.
--> keep on the guidelines and you usually don´t encounter problems.

Klaus

 

[danadakk]

Probing considerations, scope probe ground nemesis for getting bad
readings :

https://download.tek.com/document/02_ABCs-of-Probes-Primer.pdf

The datasheet has extensive recommendations on bypassing and grounding.
Elimination of those caps not a good idea, in fact lead one to find either
they have crappy ESR that you used, or some other issue. Post a pic of your
prototype, well focused I would add.

Capacitor ESR, for same value caps, one vendor to another, and their technology
matter. I did a study of .001, .01 and .1 uF caps years ago, for some RF work, vendor to
vendor huge differences. Qualify your caps with some bench testing.

Regards, Dana.

 

[Easy peasy]

Far too little information provided for helpful specific comment

 

[crutschow]

I am facing some noise only when i pwm (16KHz). I can also measure the noise on the other pins of the MCU.

Does this noise cause a problem?
If not, then why are you concerned?

 

[Easy peasy]

Welcome to the world of fast switching edges with associated high di/dt & dV/dt causing RFI and other effects ( e.g. ground bounce )

affecting your control circuits - most often due to poor layout, poor wiring and poor de-coupling.