What is the value of R_ADC in STM32G474 (the resistance of ADC multiplexors)? The datasheet does not list this parameter.

[VMich.1]

The application note AN2834 states that this parameter should be listed in the device datasheet. This is true for MCU families like F4, but not for G4. I know that there is a difference between slow and fast channels, but where could I find precise values?

[TDK]

They're also missing for the H7, even though the datasheet itself says to refer to a section. When reading the section, they're not in there.

 

Related:

https://community.st.com/s/question/0D50X00009q3AuRSAU/what-is-radc-for-stm32h743

It was only added on the F4 after a report that it was missing:

https://community.st.com/s/question/0D50X00009XkYXoSAN/what-is-radc-of-stm32f446-at-33v-value-is-missing-in-datasheet

Perhaps @Amel NASRI​ can do the same for the G4 and H7.

[TDK]

Apparently RADC "is not given" on the L4 (why?). Maybe it's the same here.

https://community.st.com/s/question/0D53W00000fnnYrSAI/what-is-radc-of-stm32l431-at-33v-value-is-missing-in-datasheet

Suggestion to use sampling time rather than RADC to determine sampling requirements:

https://community.st.com/s/question/0D53W00000hObQkSAK/radc-of-stm32g473

Since sampling times are in the G4 datasheet, presumably the official ST response would be to use those instead.

[Amel NASRI]

Hi @Vojtěch Michal​ & @TDK​ ,

As already suggested in the question mentioned by TDK, we suggest to use sampling time base on the content of the table "Maximum ADC RAIN".

This table is available only for "new" products. For other "old" products like STM32F407, you can find the maximum RADC value in its datasheet as well as the formula to calculate RAIN.

Being a generic application note, we cannot remove RADC from AN2834.

Continuing to list RADC in the note "Refer to Section 6.3.20: 16-bit ADC characteristics for the values of RAIN, RADC and CADC�? is an error. I'll submit an internal request to remove it.

Internal ticket number: 126571 (This is an internal tracking number and is not accessible or usable by customers).

I hope that my answer clarifies some ambiguities.

-Amel

[VMich.1]

Hi @Amel NASRI​  and @TDK​ ,

thank you very much for your answers and suggestions.

Nevertheless, since I would like to explain my reasoning regarding ADC configuration in my bachelors thesis, I wonder what is the technical motivation for replacing R_ADC with a table of compatible sampling times and external resistance R_AIN. Is it possible to elaborate, what is main factor to consider, e.g. temperature dependence?

Thank you.

[Amel NASRI]

Hi @Vojtěch Michal​ ,

The explanation is provided by @Igor Cesko​ here: "The Radc is not constant - it depends from temperature, VDD voltage, usage of Analog switches booster . Therefore datasheet contains values of Rain for given sampling times (worst cases)."

-Amel