STM32H747 ADC Internal Reference usage and stability

[Kranthi]

Hello

I am new to STM32 family and currently I was working on STM32H747I-DISCO board with HAL device support.

Is it possible to change the ADC reference from external Vref+ to internal Vref ? if possible how to configure? why because there is no parameter to configure ADC reference in HAL libraries.

And while using with external reference voltage Vref+ the ADC count was fluctuating even if the configured ADC channel was connected to ground. How to stabilize it?

Thank You

[berendi]

If there is a way, then you can find it in the reference manual.

HAL can't do everything that the MCU can do. The reference manual is the authorative documentation, HAL is a collection of examples that helps beginners getting started.

[Kranthi]

Thank you for your quick response.

I found VREFBUF registers in reference manual. Is it possible to configure VREFBUF registers while configuring ADC ?

In my board Vref+ was connected to +3.3.V supply, is it possible to configure internal reference?

[berendi]

Change VREF before configuring the ADC, because the ADC should be recalibrated afterwards anyway. But don't expect much improvement.

Getting stable ADC readings requres noise-free Vdda, Vssa and Vref supplies, something that cannot be fixed in software.

[Kranthi]

Thank you

[oleksandr.karbivsky]

>> Is it possible to change the ADC reference from external Vref+ to internal Vref ?

No. The internal voltage reference is internally connected to the input channel ADC3 VINP[19]. The internal voltage reference can be monitored to have a reference point for evaluating the ADC VREF+ voltage level.

From reference manual "26.4.35 Monitoring the internal voltage reference".

[Kranthi]

But according to chapter 28 Voltage Reference Buffer you can configure Internal reference voltage for ADC and DAC reference voltage and you can also select the voltage levels with VREFBUF_CSR.

I tried and configured for 1.5V, it is working.