Fast-Transient DC-DC Converter using an Amplitude-Limited Error Amplifier with a Rapid Error-Signal Control

A current mode DC-DC buck converter with fast transient response has been proposed and implemented in a commercial 0.4-μm CMOS process in this paper. The fast transient response is obtained by using an amplitude-limited error amplifier with a rapid error-signal control. The proposed fast transient control sets up or down the error signal to the maximum or minimum voltage of the amplifier during the load transient. Thus the duty cycle rapidly decrease or increase to the lowest or highest level the converter could achieve, and the overshoot/undershoot voltage is effectively reduced. Measurement results demonstrate that the transient ripple is smaller than 35 mV for a 450 mA load current step at 1 MHz switching frequency when input and output voltages are 5 V and 1.8 V, respectively. Besides, the converter only occupies an area of 1.3 mm
²
, providing a maximum load current of 1000 mA.