Fast transient response DC–DC converter with start-up in-rush current control
A new alternative to achieve fast transient response while inherently managing the in-rush current during DC/DC switching converter start-up is proposed. An AC coupled feedback (ACCF) is introduced using a capacitor multiplier from the output of the converter to the output of the error amplifier. With this additional feedback, the transient response, which used to be limited by the compensator mid-band gain has been significantly improved. Meanwhile, the ACCF circuit can help to control the converter output ramping speed during power-up, thus eliminating the bulky soft-start circuit. The simplified circuit design means the new controller can be realised by a tiny on-chip circuit, thereby minimising the footprint and the cost. A buck converter with the proposed technique is designed using 0.18 μm CMOS process and simulated across different process corners. Simulation shows that the output voltage increases linearly with the designed slope despite the variations of the input voltage, inductor or output capacitor values. An excellent load transient response of 0.021 mV/mA is achieved for a load current variation from 50 μA to 1 A in 1 μs.
