STM32F429ZI reference voltage

Question

I want to use the full output resolution of DACs (12bit) in the range of 0-1 Volt (and not in the range 0-3.3 Volt). I see there is a pin VDD in this board (STM32F429ZI), please help me to understand how use it or other pins (what is the correct connection to be used) to correctly set the desired maximum voltage of DAC. In addition, if I change the reference voltage for DAC, do ADCs consequently use this voltage or can I set different reference voltage for them?

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• Chris Stratton: Unless the data sheet specifically says you can change the DAC output voltage you will likely need a voltage divider, perhaps also with an op-amp as a buffer depending on what you are doing.
• Matt Young: st.com/resource/en/reference_manual/dm00031020.pdf

Answer 1

In the datasheet page 434 it describes how you can set a reference voltage from 1.8V but not less. If you want the DAC to have full resolution between 0-1V that's just not possible. However you would get pretty acurate readings anyway.

datasheet table

If you want to change the resolution with a new reference voltage you use a voltage divider to set the voltage (1.8V-3.3V). If you set it to say 1.8V then a reading of 1.8V in 12 bit resolution reads 4095.

Voltage divider

Since this is the lowest you can go a reading of 1V with this resolution would give you the digital number 2275 giving you a resolution of 0-2275. Alternately you could amplify the signal you are measuring to 1.8-3.3V.

• Chris Stratton: No, you can't use a step up "regulator" on an analog signal - the whole purpose of a "regulator" is to be non-linear and deliver the same output regardless of input (within range). The part to use is an amplifier with linear behavior, one of the more common forms being an op-amp in a circuit where gain is controlled by negative feedback.
• Michele M.: Therefore, considering the attached figure of microcontroller header 32x2, I can build the voltage divider starting from 5V pin and two resitors, and connect VDD pin to Vref (1.8 Volt). Is it correct? But does this connection influence only ADC channels or also DAC channels of microcontroller? In addition can I connect the board to pc-usb to download the code, with the connection realized above, or I have to disconnect it before connect USB?
• C. K.: @MicheleM. Yes you can connect the 1.8V or any other voltage to the Vref with a voltage divider. In the datasheet it says that the DAC and also the ADC uses the Vref+ so yes it affects them both. The voltage divider - to Vref does not affect your USB and vise versa. You can download the code and leave the connection as is.