ADC Sampling of Voltages > 2.8V effects VDD

[MGehr.3]

Using STM32L431RCT6 (VDDA and VREF+ bondet together). VDDA/VREF is 3.0V and VDD is 1.8V. If i'm sampling voltages larger then 2.8V that effects VDD (Jumping from 1.8V to approx. 2.06V for approx. 400ms). Any Idea's what i'm doing wrong?

[Imen.D]

Hello @MGehr.3​ and welcome to the STM32 Community :)

​What is the pin used for ADC input?

​May be it is a TT_x pin !

Imen

[MGehr.3]

Hey good to know. Yes i'm using them. I have to change them...

Unfortunately with following workaround we fixed the behavor. We were enabling and disabling the ADC. If we keep the ADC always enabled the effects on VDD are gone. It did happen always with changing the Multiplexer Inputs (Register SQR1)...

Thanks for the quick support :)

[waclawek.jan]

This is interesting.

> We were enabling and disabling the ADC.

Did you also change the mode of the related pins in GPIO_MODER, from Analog to some of the GPIO?

Thanks,

JW

[MGehr.3]

No we leave them always in Analog Mode as ADC...