STM32G431RBT6 ADC internal Vref 2.048V

[sshan.2]

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 

[TDK]

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.

[sshan.2]

Hi team,

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

[sshan.2]

 

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]

Is it Nucleo board? 

[sshan.2]

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

[MasterT]

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]

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

[TDK]

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

 

[sshan.2]

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]

> 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

 

[Billy OWEN]

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]

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]

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