STM32F405RG weird ADC spikes

[LLOLO.1]

Hi I am working on a small project where I need to sample couple of ADC channels.

I am using STM32F405RG. ADC1 is running in continuous and scan mode with DMA. I am using ping pong buffers to send ADC data through USART.

After gathering some data I plot them in MATLAB.

Problem is that there are random spikes in my ADC values an example is shown below.

X axis is Seconds, Y axis is voltage. Graph belongs to an ADC channel where approximately 2.6 volts needs to be read.

 

Has anyone encountered this ?

[TDK]

It's going to be an issue of having grounds which are separated by a potential. Typically this is solved by having a solid ground plane and tying ground pins to it with vias very close to the pin.

Is this a custom board? What does your layout look like? What else is connected to the same power/ground rails?

[tkor.1]

The first think is - you have to have straight line @ 0V when you put ground directly on ADC pin. The spikes comes from your ADC wiring, without drawing and picture of it, it is just guessing work.

[waclawek.jan]

ST has AN2834 and AN4073 as guidelines to the ADC.

JW