STM32 Power supply ripple voltage

[shin212]

Hi, 

What is acceptable ripple voltage on power supply pins on stm32? 

I am using DC/DC converter and have 100mVpkp at the output (+3.3V). I tied VDD and VDDA pin to one power supply as I am not planning to utilize an internal ADC. I am just planning to use this mcu to read analog signal from an external ADC and generate PWMs. Is 100mVpkp critical for this application? I have attached a snapshot of the schematic! Let me know if I need to clarify anything. Thank you 

[Pierre_Paris]

Hello @shin212,

Thank you for your question!

What is the exact name of the STM32F1 you are using ?

I don't think 100mVpkp is critical in this case. Indeed, I saw in your snapshot you respected the power supply scheme of the DS. The capacitors will filter the ripple.

Can you consider trying your converter with the ripple on the 3.3v as an external source on a Nucleo-STM32F1 and verify proper operation ?

Best Regards,

Pierre

[shin212]

Hi, 

It's stm32F103CBT6. I already tried with an external power supply and provide power to mcu. With an external power supply (3.3V)there is less noise (Almost none) .100mVpkp dose not get reduced with decoupling capacitors and with increasing output capacitor of DC/DC converter! 

[LCE]

I'd rather try to reduce the ripple at the source.

Check inductor and capacitors of the switching regulator, and the layout: switching power paths must be as short as possible, especially GND of input caps, output caps and IC must be as short as possible.

[Pierre_Paris]

Have you consider a BEAD for your application between the VDD and the VDDA ?

Also, its really restrictive.

[LCE]

Unless the ripple is >> 1 MHz a ferrite bead won't help much.

[Pierre_Paris]

I just found this application note about designing with STM32 in noisy environments.