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Recommended course of action for Unused pin of STM32 MCU

Forum|Forum|2 years ago
August 14, 2023
4 replies
16751 views

Dear ST Community members

I am currently designing a PCB and utilizing the STM32G473VET6 MCU. I have noticed that there are several unused pins. Should I leave these pins unconnected or is there a recommended course of action for dealing with them?

thanks and regards

Neeraj

stm32g473cb.pdf

STM32G4 series

This topic has been closed for replies.

Best answer by KDJEM.1

Hello @Neeraj and welcome to the Community :),

Do not leave unused pin floating. You can connect these unused pins to ground or to supply on the PCB, or use PU / PD.

The unused I/O pins should be configured as analog input by software; they should also be connected to a
fixed logic level 0 or 1 by an external or internal pull-up or pull-down.

For more explanation I advise you to refer to Getting started with STM32G4 Series hardware development boards application note.

As already mentioned by @KnarfB the AN4899 Application note" STM32 microcontroller GPIO hardware settings and low-power consumption" can help you and precisely Avoid floating unused pin section.

I hope this help you!

Kaouthar

KnarfB

Super User

AN4899 Application note" STM32 microcontroller GPIO hardware settings and low-power consumption" is your friend.

hth

KnarfB

N

NeerajAuthor

Associate II

Hi @KnarfB

Is it possible to connect unused pins to ground or VCC without a pull-up/down resistor?

KnarfB

Super User

Well, I won't take any responsibility for your design. @KDJEM.1 has pointed you to more reading. Keep in mind that the empty check on a virgin device may push or pull pins in unwanted directions as discussed here https://community.st.com/t5/stm32-mcus/empty-check-mechanism-on-stm32/ta-p/49369

hth

KnarfB

KDJEM.1Best answer

ST Technical Moderator

Hello @Neeraj and welcome to the Community :),

Do not leave unused pin floating. You can connect these unused pins to ground or to supply on the PCB, or use PU / PD.

The unused I/O pins should be configured as analog input by software; they should also be connected to a
fixed logic level 0 or 1 by an external or internal pull-up or pull-down.

For more explanation I advise you to refer to Getting started with STM32G4 Series hardware development boards application note.

As already mentioned by @KnarfB the AN4899 Application note" STM32 microcontroller GPIO hardware settings and low-power consumption" can help you and precisely Avoid floating unused pin section.

I hope this help you!

Kaouthar

To give better visibility on the answered topics, please click on "Best answer" on the reply which solved your issue or answered your question.

MVeen.1

Associate II

Hi @KDJEM.1 ,

The AN4899 application note section "Avoid floating unused pin" also recommends setting the pin as PP output driven low for ESD concerns.

-So generally we should always set unused GPIO to analog input and Pull Down and that should be okay for noise?

-And if we are concerned about ESD we switch to the PP output?

KDJEM.1

ST Technical Moderator

Hello @MVeen.1 ,

Noise on non-connected input pin is a source of extra consumption by making the input buffer switch randomly. So, it is recommended to connect unused pins either to ground or to supply on the PCB, or use PU / PD. If the application is sensitive to ESD, prefer a connection to ground or define the pin as PP output and drive it to low.

Thank you.

Kaouthar

To give better visibility on the answered topics, please click on "Best answer" on the reply which solved your issue or answered your question.

TDK

Make sure you don't tie pins needed for programming to ground. If you're using the system bootloader, make sure you don't tie things to ground that it needs to function.

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