Initial/Last-State-Correlated SAR Control with Optimized Trajectory to Reduce Reverse Overshoot and Smooth Current Switching of Hybrid LDOs

Conventional successive approximation recursive (SAR) control hybrid low-dropout regulators (LDOs) have problems such as significant reverse overshoot and discontinuous current switching. Based on trajectory optimization in the phase plane, this paper presented initial/last-state-correlated SAR control to address the aforementioned issues. Firstly, the operating principles of the conventional SAR controller are elucidated, which is depicted by a finite state machine (FSM). Secondly, large reverse overshoot and discontinuous current switching of the SAR control hybrid LDO are analyzed through the phase plane trajectory. Then, the initial/last-state SAR control is proposed by FSM to optimize the trajectory, thereby reducing the reverse overshoot and smoothing current switching. Finally, a series of design challenges of the initial/last-state-correlated SAR control are discussed. Implemented at 1.11 mm × 0.567 mm in a 180 nm bipolar-CMOS-DMOS (BCD) process, under a 0.1 nF output capacitor, the 6-bit hybrid LDO in this paper achieved an output voltage overshoot of 76 mV and a transient time of 18.8 μs at a 152 mA load current change. The experimental result demonstrates the distinct dynamic response advantages of the initial/last-state SAR control.