A Fast-Transient and High Stability LDR Based on Capacitive-Coupling Method

A fast transient response Low Dropout Regulator (LDR) is designed, which is based on Capacitive-Coupling Method (CCM). When the load currents step between no load and full load, the improved voltage buffer can dynamically change the current to charge or discharge the gate of the regulation transistor to rapidly inhibit overshoots or undershoots of the LDR and shorten the recovery time. By employing the current-buffer and Equivalent Series Resistance (ESR) compensation methods, the stability of the LDR can be ensured in a wide range of the load currents. The LDR is designed with 0.18 μm standard CMOS process. Simulation results show that the regulator dissipates 35 μA at no load and 80 μA at full load. The output capacitor of designed LDR is 2.2 μF. The LDR reveals the step-down transient response time of 438 ns and the overshoot of 4.2 mV at the load stepping from 100 mA to 0. The step-up transient response time and undershoot voltage are 385 ns and 12.9 mV, respectively, at the load stepping from 0 to 100 mA.