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 ?

[tkor.1]

Do you have spikes when you put input to ground ?

[LLOLO.1]

ground has also spikes.

[Ozone]

That doesn't sound good.

A proper and stable power supply at least for the analog branch (Vdda) is required to get stable results.

Sounds like a PCB redesign for me ...

[waclawek.jan]

> I am using ping pong buffers to send ADC data through USART.

Try to disconnect any unnecessary connections, including the USART, store the data in RAM, dump them later after connecting the USART.

JW

[LLOLO.1]

I am doing exactly that right now. There is nothing else connected.

[tkor.1]

Try to run another program such as DC voltmeter, check for spikes DAC pin on grand, you should have straight pure line on 0V. For grounding use wire jumper not a capacitor.

[TDK]

> ground has also spikes.

If you're tying "ground" to the ADC channel input and you still see spikes, it's unlikely to be a software issue and unlikely to be a problem than can be fixed by software changes. The SAR ADC within the STM32F4 isn't going to read significantly more than 0 counts in this configuration. It could be that the "ground" you're tying is a different potential than "VSSA," at least during some transient periods. Could also be something damaged in the ADC itself, but seems less likely to me.

[LLOLO.1]

So assuming it is not a software issue, where should I look first? VDDA line?

[LLOLO.1]

I checked VDDA and its stable during sampling.

[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