DAC / ADC output voltage function of STM32F303

[v_]

Posted on May 10, 2013 at 14:35

Hi,

There is a STM32F303 pin for VREF+ of DAC and ADC (in common). I would have suspected that this reference voltage input does adjust the conversion function in such a way that Vout max of DAC (i. e. digital FFFhex) = Vref+ andOutput value of ADC at input of Vref+ = FFFhex. But I can't find any formula in the reference manual for the ADC conversion function. The only formula I could find is one for the DAC at page 306 of the reference manual which does look suspicious:

DACoutput = V

DDA* (DOR/4095) This seems to me to be a special case where Vref+ input pin is connected to VDDA. Has anyone experience with the ADC / DAC and could help me with that topic? #stm32f303 #adc #dac #vref+

[Tesla DeLorean]

Posted on May 10, 2013 at 18:43

Yes, the documentation is not entirely helpful, in many case the VDDA is bonded to VREF+. The only reasonable purpose of providing VREF to the DAC would be as that DACoutput = VREF * DOR / 4095

It surely wouldn't take much effort to prove on a part with separate supplies for VDDA and VREF+. I think there have been complaints about not quite touching the rails (ie 0x000 and 0xFFF)

[v_]

Posted on May 13, 2013 at 08:19 Thx Clive, I've finally found the information in the reference document on page 80:

6.1.1 Independent A/D and D/A converter supply and reference voltage

To improve conversion accuracy, the ADC and the DAC have an independent power supply which can be separately filtered and shielded from noise on the PCB.The ADC and DAC voltage supply input is available on a separate VDDA pin. An isolated supply ground connection is provided on the VSSA pin.

100-pin package connections

To ensure a better accuracy on low-voltage inputs and outputs, a separate external reference voltage can be connected on VREF+.

VREF+ is the highest voltage, represented by the full scale value, for an analog input (ADC) or output (DAC) signal.

64-pin and 48-pin package connections

On these packages, the VREF+ and VREF- pins are not available, they are internally connected to the ADC voltage supply (V

DDA

) and ground (V

SSA

) respectively

...

[per23]

Posted on October 01, 2014 at 11:21Hi!So if I'm using the 48-pin package I can't use the internal reference ( ~1,2 v) for DAC output. Is that correct or have I misunderstood? I'm trying to get the best possible accuracy on my DAC output and therefore I would like to use the internal reference if possible but I haven't found out how to do that.Thanks for your help!BRPer

[Tesla DeLorean]

Posted on October 01, 2014 at 11:31

So if I'm using the 48-pin package I can't use the internal reference ( ~1,2 v) for DAC output. Is that correct or have I misunderstood?

I don't think the pin count makes a difference, VREF+ != VREFINT