STM32F0 ADC Accuracy

[Nuppo]

Posted on May 31, 2018 at 11:34

Hi, everyone. I've been using STM32F030F4P6 for a project. 

While prototyping the circuit that I am going to use on my project, I shorted Vdda and Vdd pins together with 10uF and 100nF capacitors to the ground. I am giving exact 3.3V to these pins with an DC power supply.

The problem is my voltage readings are usually

�

50mV off. My ADC configuration; continuous mode with software trigger with only EOC interrupt, SMPR set to highest (111). I've also used Vref to calibrate Vdda. Using Vref made results a bit better (Not that much). But it didn't make a lot of sense to me since Vref_int data was 1472 and Vref_cal was 1536. This tells me Vdda that I'm giving is 3.44V which is not true at all.

How can I improve this MCU's ADC? Should I seperate Vdda - Vdd and give a voltage reference to Vdda? Would these improve my readings that much?

#adc-supply #stm32f030 #stm32f0 #adc-configuration #adc-calibration

[Nesrine M_O]

Posted on May 31, 2018 at 11:38

Hi

nuppo

,

I recommend you to have a look to the

http://www.st.com/content/ccc/resource/technical/document/application_note/group0/3f/4c/a4/82/bd/63/4e/92/CD00211314/files/CD00211pdf/jcr:content/translations/en.CD00211pdf

Application note aboutHow to get the best ADC accuracy in STM32 microcontrollers.

-Nesrine-

[henry.dick]

Posted on May 31, 2018 at 12:07

'

The problem is my voltage readings are usually

±

50mV off.'

1. have the right expectation;

2. use calibration;

3. some of the chips, i think F0 is one of them, have adc calibration stored in the chip. that greatly improve the accuracy.

4. make sure you are measuring right.

[T J]

Posted on May 31, 2018 at 15:24

Yes F0 has the calibration function and it works well.

final results are close to only 1mV error.

[Nicholas Yunker_2]

I am having the exact same problem on an STM32F070. tie the VDDA pin to VDD through a ferrite bead (to filter the input to VDDA) which is 3.319V. My analog input is a solid 0.6V (verified by 2x multimeters and an O-Scope). The MCU ADC measures 679 counts and it calcuates out to be approx 0.55V. According to my math at 0.6V I should be getting 740 counts. This is approx. 60 count / 50mV difference.

Have you found a solution to your problem that you can share?

[raptorhal2]

The ADC reads the sample & hold capacitor, which is not accessible to a multi meter. Ensure you have a low impedance signal, or set the sampling time high as explained in Nesrine's application note reference. Grounding unused ADC channel pins can also help.

Cheers, Hal

[Nicholas Yunker_2]

​Hal,

Thank you for responding, when I said I used a multimeter I meant I checked he incoming signal...not the inaccessible internal caps.  I do have a low impedance signal, I am running the signal through a unity gain buffer (opamp).  I have also tried changing he sampling rate with no effect.

I did speak with a person that works for ST Microelectronics after posting here and he said it sounds like I have to calibrate the ADC.  I am going to try that and see if it fixes the issue.

Nick

[Nicholas Yunker_2]

​Ran the HAL_ADCEx_Calibration_Start(&hadc) command and that fixed it.  ADC Is reading very accurate now.