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How does this circuit work?

Category: Hardware
Product Number: CN0410

Dear Sir:I have two questions about the CN0410,the part of Voltage to Current Conversion.
The operational amplifier is used as an integrator to drive the MOSFET by integrating the forward input voltage. The input voltage of the integrator is from the DAC(up to 2.048 volts).
Problem 1: No matter how small the input signal is, after a period of integration, it will eventually saturate the output of the integrator, that is to say, the VG voltage of MOSFET can basically saturate to the supply voltage. Resulting in Vgs=3.3 volts. As a result, the current passing through the MOSFET is constant. How can it adjust the current?
Question 2: IMAX=2.048V/R(2Ω) is used to calculate the maximum value of the current. Why use 2.048V instead of the power supply (VS).So ,I think,the formula should be IMAX=VS/R(2Ω),is that right?
thanks for your answer.