Design of 300nA quiescent current and 300mA load capacity LDO with fast transient response

This paper presents a low dropout regulator (LDO) with a low quiescent current which helps to extend the standby time of battery-powered electronic devices. By utilizing the switchable bias technique in the error amplifier (EA), the bias current is switched to a higher level to accelerate the transient response under heavy load, while a low bias current is applied to EA to maintain a low quiescent current under light load. High speed current comparators and hysteresis control are combined to ensure fast and stable switching operation of the bias current. Moreover, an inrush current suppression circuit is proposed by recycling the switchable bias in EA. During startup, the bias current of EA can be kept low, and a reduced slew rate can be obtained at the pass gate voltage. The proposed LDO has been fabricated in 0.18-mu m CMOS process, The experimental total quiescent current is 300nA under no-load condition. The maximum load current is 300mA. Measurement results show that the LDO can be settled within 8 mu s for a load current step of 0-50mA. In the startup process, the measured inrush current can be effectively limited.