Fast transient capacitor-less LDO regulator using low-power output voltage detector

An output-capacitor-less low-dropout regulator (LDO) with a low-power output voltage detector (OVD) is proposed. The OVD is based on an R/C highpass filter which is able to detect the fast-changing voltage at the LDO output and activate an additional path to control the power transistor. The OVD consumes only additional quiescent current to monitor the variation in output voltage in the steady state. In the simulated load-transient response, a maximum undershoot of 1.2 V and a settling time (Δt₂) of 67 ns are observed with the proposed OVD for a load current variation from 1 to 50 mA at a rise time of 1 ns. These results are 0.2 V and 473 ns better than the results obtained without the proposed OVD.