Hi,
a design starts with requirements and technical specifications.
Requirements here are:
* "using OPAMP"
* "LDO" .. Voltage, current? What is it used for? As output device that needs to be "controlled by the OPAMP" or is it used as the OPAMP supply.
* "DAC"... and what´s it´s function. Is it to compensate drifts only, or to set outut voltage and/or current... or any other function
Technical specifications come with numbers and units: This means you need to decide and give numbers for:
* supply voltage
* temperture sensitive (whatever this means)
* voltage stability / variation
* "flexibility" (whatever this means)
* noise
(this list is accorsing your text)
BUT: You miss a lot of important things:
Like:
* What´s the input power supply, with it´s noise and it´s variations?
* what´s the expected output voltage (range)?
* what´s the expected output current range?
* everything that describes teh DAC: bit resoluuton, drift, accuracy, precision..... and most of all: what is the DAC expected to do?
A circuit is hard to be described in three lines of text (even for professinals). Thus please provide something like a schematic .. at least a draft, that shows all your "parts" and how they interact (aare connected) with each other. Pictures are way better to describe such things .. especially when crossing language borders ... and one is not familiar with technical terminology.
Klaus