During the test, we found that the reference voltage of DAC channel 1 for STM32L4P5is 3V，while the VREFBUF for channel 2 is 2.048V，they are not identical，and the VREFBUF->CSR value is 2.

[HAlex.1]

..

[waclawek.jan]

And what's the actual voltage on VREF+ pin? Don't you have connected 3V to it externally?

You may also want to read https://community.st.com/s/article/how-to-configure-vrefbuf-on-my-stm32

JW

[HAlex.1]

Yes, the VREF is connected to 3V externally.

[HAlex.1]

We found that if the DAC output is connected with a 100K resistor, it is 3V, while if it is connected to a 27K resistor , the output is lowered to 2V. Does it because of the driver?

[waclawek.jan]

What do you mean by "driver"?

The DAC's current driving capability is small, see datasheet. You can switch on a buffer, but then the output won't go all the way to the rails.

JW