My LED has a threshold of 3.7V, evaluation board is powered with 1to 5V, and microprocessor needs 3to 4V and the DAC needs Vdd around 2.7V to 5.25V and Vrefin= 1.25V. How do I take care of the voltages of the design ?

 

Since everything except V(refin) can use either 5V or can be powered from the 5V through an LDO, a 5V supply seems ideal.

For V(refin), a programmable voltage reference, like this one, will work.

 

I’d go for 3.3V for everything except the LED. The LED can be driven by a transistor and be connected to any supply voltage ≥5V with the appropriate current limiting resistor.
Doesn’t the microcontroller have a built in reference?
LP2951 is my favourite voltage regulator. It is reasonably low dropout, accurate enough to be used as a reference, and can be supplied by any voltage up to 35V.

 

I’d go for 3.3V for everything except the LED. The LED can be driven by a transistor and be connected to any supply voltage ≥5V with the appropriate current limiting resistor.
Doesn’t the microcontroller have a built in reference?
LP2951 is my favourite voltage regulator. It is reasonably low dropout, accurate enough to be used as a reference, and can be supplied by any voltage up to 35V.

Considering it, I think @Ian0 is right, 3.3V to the parts from a 5V main supply covers everything and is more flexible if you add things that are not 5V tolerant.

 

You can also use separate 3.3V LDOs if, for instance, you would like to give the DAC its own supply to keep out noise from the MCU.