STM32 ADC Vref+ & VDD

[markjohnson9]

Posted on March 25, 2015 at 16:47

An application requires an external Vref+ of 3.0VDC and Vref- of 0, VDD of the chip is 3.3VDC. Whats the best method to set this Vref+ to the STM32 micro controller?

[Tesla DeLorean]

Posted on March 25, 2015 at 16:52

I don't understand the question, apply the external source to the pin?

[markjohnson9]

Posted on March 25, 2015 at 20:17

The data sheet indicates that the Vref+ is tied to VDDA(ADC volts) and VDDA has to be greater than or equal to VDD(chip supply voltage). So if VDD is 3.3V then VDDA has to be greater than or equal to VDD. With a 3.3V VDD, the ADDA voltage has to be 3.3V or larger. Up to 400mv max so ADDA is to be no more than 3.7VDC.

[Tesla DeLorean]

Posted on March 25, 2015 at 20:35

Then consider using a part that doesn't tie the pins together, or run the chip at 3.0V too? A lot of the parts/pins would permit connectivity to other 3.3V-5V chips in the design. All the DISCO boards run at 3.0V, as I recall.

ST makes a few STM32 parts, care to be more specific?

[markjohnson9]

Posted on March 25, 2015 at 21:34

The microcontroller I was originally going to design in was  STM32F030R8, 64 pin LQFP64 package, a nice low cost device. However the ADC Vref+ became an issue.

In app note AN2834 pg. 23 sec 3.2.5 Matching the ADC dynamic range to the maximum signal amplitude, indicates that the Vref+  may range between 2.4V and VDAA if a 100/144 pin package was used. Reviewing STM32F071V8T6 data sheet, a 100 pin device, internally ties VDDA to Vref+ with no method/pin to externally set Vref+, very frustrating. Does anyone know of an STM32 part that can externally set the ADC Vref+ on a separate pin that is not tied to the VDDA? If not I will have to seek another mfg device that allows this requirement.

[Tesla DeLorean]

Posted on March 26, 2015 at 01:29

STM32L151/152 LQFP100,TFBGA64,UFBGA100

STM32F105/107 LQFP100 STM32F205/215/207/217 LQFP100,LQFP144,LQFP176,UFBGA176 STM32F405/415/407/417 LQFP100,LQFP144,LQFP176,UFBGA176