This paper proposes an external capacitor-less low-dropout (LDO) regulator with undershoot and settling time reduction technique for fast transient response. In the proposed LDO, a feedback capacitor is applied instead of a complicated voltage-spike detection circuit to reduce undershoot voltage and settling time without consuming additional quiescent current. When the undershoot voltage occurs in the load transient response, the gate charging current of the pass transistor is rapidly increased by the current flowing in the feedback capacitor to reduce the undershoot voltage. When the overshoot voltage occurs, the gate charging current to reduce the settling time. The proposed LDO regulator is implemented with a 0.18 μm CMOS process and consumes a quiescent current of 3.0 μA at a minimum load current of 0.1 mA and 230 μA at a maximum load current of 50 mA. Compared with the conventional LDO regulator, the proposed LDO regulator reduces the undershoot voltage by 53.3 % and the settling time by 55.5 % without consuming additional quiescent current.
