Other Parts Discussed in Thread: REF3312
Would you tell me about minimum rating of input voltage?
It isn't mentioned in the datasheet of REF33xx.
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The minimum input voltage is determined by your output voltage plus the required dropout voltage. The typical dropout is 110mV, but here is a graph from the datasheet that shows the relationship between the dropout and output current.
In summary, for worst case scenario, the minimum Vin for the REF3325 is 2.7V.
There is no minimum voltage under absolute maximum ratings because having a lower voltage won't damage the part, as long as it is above ground.
That being said, the graph on the post above shows what the minimum dropout needs to be for the part to begin to regulate. The max current draw determines how much dropout voltage is needed. I ran a quick test in the lab with a REF3312 and it needed 20mV to be within 0.15% of 1.25 with 10uF capacitors.
It is important to note that the part's performance is specified under the recommended operating conditions, as the drop out decreases from 200mV so will the performance.