A stable compensation scheme for low dropout regulator in the absence of ESR

A new compensation scheme for low dropout regulator (LDR) in relaxing the constraint on the equivalent series resistance (ESR) down to the value of zero from no load to full load current condition is presented. This is achieved by introducing a load-tracking zero that tracks with the moving output pole as the load current varies, and a level shift buffer reduces the size and capacitance of the power transistor. The load-tracking circuit ensures the stability in full load current range even in the absence of ESR. The proposed LDR is fabricated with a standard 0.35μm CMOS technology. Measurement results at very small value ESR (10mΩ) and output capacitor (0.47μF), where this equivalent ESR zero is far beyond the compensation region of LDR, confirm the stability at ESR equivalent value to be zero. Also the proposed compensation scheme allows a wide range of ESR from equivalent 0Ω to 20Ω and load capacitor from 0.47μF to 22μF with a load current of 0μA to 100mA at dropout voltage of 0.2V. © 2007 IEEE