The result I am looking for is the digital code scaling the output, but with the range being variable by (RefP - RefN):
V_Out = Digital code * (RefP - RefN)
However I need to be able to have both voltages varying, sometimes with RefN > RefP, and positive voltages on both RefP and RefN.
e.g. RefN and RefP both varying between 3V-0V independently
Are there any parts where this is possible?
Any help much appreciated!
Unfortunately, most DACs that support differential references require a certain polarity for the internal switch structure to operate. You can see in the DAC8871 datasheet that we require that VREFP>VREFN.
You could do something similar to this with an MDAC, where you can have a negative reference. You can create a new reference voltage based on the differential value of your two reference voltage, and then sum the output signal to one of the references.
See this sketch:
Thanks,
Paul
