1. Field of the Invention
The invention relates to a droop circuit, and more particularly to a multi-phase DC-DC converter with a droop circuit.
2. Description of the Related Art
In general, a droop circuit can control a swing of an output voltage in a DC-DC converter. FIG. 1A shows an output voltage of a DC-DC converter without a droop circuit, and FIG. 1B shows an output voltage of a DC-DC converter with a droop circuit. As shown in FIG. 1A, the output voltage is operated at a normal voltage Vnom except for a time t1 and a time t2. Transients of the output voltage are generated due to an output current I1 which is varied with a load of the DC-DC converter, and rapidly increases and decreases at the time t1 and the time t2. Referring to FIG. 1B, an output current I2 of the DC-DC converter with a droop circuit rapidly increases and decreases at a time t3 and a time t4. The output voltage is operated at a minimum voltage Vmin during a duration between the time t3 and t4. However, the output voltage is operated at the normal voltage Vnom outside of the duration between the time t3 and t4. Thus, for a DC-DC converter, transients of the output voltage are avoided by the droop circuit.
FIG. 2 shows a conventional multi-phase switching regulator disclosed in U.S. Pat. No. 6,683,441. In FIG. 2, an amplifier circuit 28 generates a voltage Vcs according to an output voltage Vout and a summing voltage of a summing node 26. Then, the output voltage Vout is subtracted from the voltage Vcs to generate a droop voltage Vdroop by a summation circuit 30. Thus, the multi-phase switching regulator needs the summation circuit 30 to obtain the droop voltage Vdroop, and the output voltage Vcs of the amplifier circuit 28 is equal to the output voltage Vout plus the droop voltage Vdroop. FIG. 3 shows a conventional droop amplifier circuit disclosed in U.S. Pat. No. 7,064,528 for generating a droop voltage VDROOP. In FIG. 3, a positive polarity (+) of the droop voltage VDROOP is provided by an output of an amplifier A2, and a negative polarity (−) of the droop voltage VDROOP is provided by an output node of a multi-phase DC-DC regulator. Hence, an output voltage of the amplifier A2 is equal to an output voltage VOUT of the multi-phase DC-DC regulator plus the droop voltage VDROOP.