DC-DC converter and error amplifier thereof

A DC-DC converter, comprising:

• a DC voltage source;
• an output capacitor, coupled to the output terminal of the DC-DC converter;
• an error amplifier, comprising:
• an operational transconductance amplifier, generating a first current according to the voltage difference between a reference voltage and a feedback voltage, wherein the feedback voltage is dependent on the output voltage of the DC-DC converter;
• a compensation circuit, comprising a compensation resistor, a compensation capacitor, and a Miller circuit operated in a first mode or a second mode, wherein the first terminal of the compensation resistor is coupled to the output terminal of the operational transconductance amplifier, the first and second terminals of the Miller circuit are respectively coupled to the second terminal of the compensation resistor and the first terminal of the compensation capacitor, the capacitance of the compensation capacitor charged or discharged by a second current is Cz, the equivalent capacitance generated by the Miller circuit and the compensation capacitance is (1+k)Cz where k is a positive constant value determined by the Miller circuit, the second current in the second mode is (1+mk) times that in the first mode where m is a positive decimal fraction determined by the Miller circuit;
• and
• a fast transient controller, switching the Miller circuit to the second mode when the feedback voltage exceeds a high voltage level or falls below a low voltage level, otherwise the Miller circuit is set in the first mode;
• a pulse generator, generating a pulse signal according to the voltage level of the output terminal of the operational transconductance amplifier;
• and
• a power stage circuit, coupled to the DC voltage source and the output capacitor, and charging or discharging the output capacitor according to the pulse signal to maintain the output voltage level of the DC-DC converter at a stable value.