I need to build a very stable DC power supply with a variable output (51 to 56 VDC) at a very low current output ( 100 mA). But the driff and stability needs to be very less than 5 mV. The circuit will not be operating in very significant temperature changes. Which of the many Linear voltage reference should I be considering for this application?
The design that you are considering is not trivial, and thereare several factors that you will have to consider. The voltagereference is key, of course, but you also need to have a low-offset,low-drift amplifier for your gain loop, and low-drift, low-Tcresistors for feedback. You may also have to consider noise, sinceloop gain will be considerable. And, of course, PCB stresses willmatter, so carefully consider layout effects.
For your voltage reference I suggest the LT1027DCLS8-5Precision, Low Noise, High Stability Hermetic Voltage Reference. Foryour gain amplifier I suggest the LTC2957HV High Voltage, Low NoiseZero-Drift Operational Amplifier. For the feedback resistors I suggestthe LT5400 Quad Matched Resistor Network. Finally, to add some currentoutput capability, you can include the LT3088 800mA Single ResistorRugged Linear Regulator in the feedback loop.