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Neeraj
Associate II
August 14, 2023
Solved

Recommended course of action for Unused pin of STM32 MCU

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

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KDJEM.1
KDJEM.1Best answer
ST Technical Moderator
August 14, 2023

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.
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15 replies

KnarfB
KnarfB
Super User
August 14, 2023

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

hth

KnarfB

    NeerajAuthor
    Associate II
    August 14, 2023

    Hi @KnarfB 

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

    KnarfB
    KnarfB
    Super User
    August 14, 2023

    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.1
    KDJEM.1Best answer
    ST Technical Moderator
    August 14, 2023

    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
    MVeen.1
    Associate II
    October 4, 2023

    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
      KDJEM.1
      ST Technical Moderator
      October 4, 2023

      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
      TDK
      August 14, 2023

      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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