For what use is this circuit?
Here is its datasheet and it is a positive fixed voltage regulator.

Through pin 2 enters a voltage not greater than 6V and on pin 3 it outputs 1.5 V as long as:


the load doesn't draw more than 250 mA
the input voltage is with 250 mV greater than the output voltage


See the datasheet for full specifications.

In the schematic you provided, this IC:


is powered via AVDD with approximately 2.8 V
the output is available on DVDD