Why won't my DAC output a voltage larger than 2.56v?

[RWang.9]

Hi there,

I've been having difficulty trying to make the DAC channel 1 output 3.3v. The largest voltage that the DAC outputs is 2.56 volts which I measured with an oscilloscope. I try to set the output voltage to be higher with the following code snippet but the DAC doesn't output anything higher than 2.56 volts.

HAL_DAC_SetValue(&hdac, DAC_CHANNEL_1, DAC_ALIGN_12B_R, 4000);

I am using the stm32cube ide and there isn't many much I can configure for the DAC. I don't know if this is a configuration issue or a hardware issue.

[RWang.9]

Do you know where I can find the DAC's internal reference voltage? I can't seem to find its reference voltage from the electrical schematics. Could it perhaps be in the configuration setting?

[AScha.3]

[RWang.9]

After looking at the schematics again I find VDDA and VREF+ are both connected to a 3.3V source. So why is the max output voltage for the DAC stuck at 2.56V?

 

Does it have something to do with pin PB1?

[AScha.3]

it would be less guesswork, if you give the cpu type...

[RWang.9]

I'm using the stm32 Nucleo-F302R8 MCU.

[AScha.3]

is any load on dac output? and try with buffer on/off .

what you get with 2048 as data ?

[RWang.9]

I don't have any load attached to the output. Turning the buffer off makes the DAC output very small voltages in the 100-200mv range.

When the data is set as 2048, I get an output of 1.8320 V. At 4096, the output is 2.61V.

Do these numbers seem reasonable?

[RWang.9]

*4095 actually not 4096

[waclawek.jan]

> Turning the buffer off makes the DAC output very small voltages in the 100-200mv range.

That sounds much like you do have a load on the given pin.

Which pin is it, btw? Is it set to Analog (read out and check/post content of GPIOA registers).

JW