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sshan.2
sshan.2
Associate III
April 23, 2025
Solved

STM32G431RBT6 ADC internal Vref 2.048V

  • April 23, 2025
  • 8 replies
  • 1507 views

Hi Team,

We are using STM32G431RBT6, we have tested the ADC1 for PA3 i.e. Channel4 with external Vref 3.3 and VDDA 3.3 with 12-bit selection and the reading we are getting with 5 to 10 counts fluctuations we are seeing but when we have changed to internal voltage ref selection for 2.048 then the PA3 i.e. Channel4 is fluctuating more than 1000 counts! but it works fine for PA0!

VDDA remains same 3.3v for both our internal and external voltage.

Please suggest us how to resolve this?? 

Thanks 

Best answer by TDK

TDK_0-1745502167020.png

So VREF+ isn't connected to anything? Seems like an issue to me. Should have caps on there.

TDK_1-1745502268530.png

 

8 replies

TDK
TDK
Super User
April 23, 2025

The ADC is a multiplexer. Hardware downstream of the pin is the same for all channels, so this must be related to what's connected to the pin (or a misinterpretation). Show the hardware schematic and connection details and a plot of the data coming out if possible.

"If you feel a post has answered your question, please click ""Accept as Solution""."
sshan.2
sshan.2Author
Associate III
April 24, 2025

Hi team,

I am attaching the code and schematic with results please look and help us 

image _stm32chik.jpeg

sshan.2
sshan.2Author
Associate III
April 24, 2025

sshan2_0-1745480107980.png

sshan2_1-1745480211774.png

sshan2_2-1745480235754.png

 

we have given 200mV and we need to get 400 counts, but we are getting values in between 250 to 430 counts.

I am unable to upload the video  

MasterT
MasterT
Lead II
April 24, 2025

Is it Nucleo board? 

sshan.2
sshan.2Author
Associate III
April 24, 2025

Yes Nucleo -G431RB (NUG431RB$AT3) Board and also same Microcontroller is used in our customized board.

MasterT
MasterT
Lead II
April 24, 2025

This is nucleo board, likely PA2 & PA3 assign to serial port. Locate product description page on ST.com, navigate to CAD docs - get schematic. Also download and study nucleo board manual.

sshan.2
sshan.2Author
Associate III
April 24, 2025

but we have not enabled any serial ports for this PA3 and PA2, only PA3 is used for channel4

TDK
TDKAnswer
Super User
April 24, 2025

TDK_0-1745502167020.png

So VREF+ isn't connected to anything? Seems like an issue to me. Should have caps on there.

TDK_1-1745502268530.png

 

"If you feel a post has answered your question, please click ""Accept as Solution""."
    sshan.2
    sshan.2Author
    Associate III
    April 24, 2025

    yes Vref+ pin is not connected any capacitors, but we can see 2.048 on multimeter.

    can you please suggest right value of capacitor to connect?? or should follow the same as shown above image??

    TDK
    TDK
    Super User
    April 24, 2025

    > or should follow the same as shown above image??

    Yes. Or follow the reference design in the hardware guide.

    https://www.st.com/resource/en/application_note/an5093-getting-started-with-stm32g4-series--hardware-development-boards-stmicroelectronics.pdf

     

    "If you feel a post has answered your question, please click ""Accept as Solution""."
    Billy OWEN
    Billy OWEN
    ST Employee
    April 24, 2025

    Hi @sshan.2 

     

    This post has been escalated to the ST Online Support Team for additional assistance.  We'll contact you directly.

     

    Regards,

    Billy

     

    sshan.2
    sshan.2Author
    Associate III
    April 24, 2025

    Hi Billy,

    as we are struck at this point and please let us know which email ID, we need to send the query??

    can we get instant chat support for this??

    Chris21
    Chris21
    Associate II
    April 24, 2025

    As MasterT already said, if you are using a Nucleo board, PA3 is likely used for serial communication to the ST-LINK:

    Chris21_0-1745517883424.png

     

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