A reference voltage register stores a reference value Vref indicating the output
voltage Vout of a power supply circuit. A digital filter amplifies the difference
between the output voltage Vout from the power supply circuit and the reference
value Vref stored in the reference voltage register. A pulse width computation
unit computes the duty such that the output voltage Vout matches the reference
value Vref, and generates the on-time of a pulse signal corresponding to the duty.
A reference value operation unit updates the reference voltage register depending
on the output current from the power supply circuit or the temperature around the
power supply circuit.
