Fast-transient, light-load efficient DC-DC converter using an auxiliary D-LDO

A current-mode DC-DC buck converter with a parallel auxiliary digital-LDO has been proposed and simulated in a
$0.18-{\mu}m$
CMOS process in this paper. The proposed auxiliary digital LDO can provide both sink current and source current, which improves the transient response by rapidly injecting a positive or negative current into the output to effectively reduce the overshoot/undershoot voltage. Besides, the digital LDO is also activated and provided the out current during the light load to improve the efficiency. Simulation results demonstrate that the transient ripple is smaller than 60 mV with 800 mA load current step and 1 MHz switching frequency when the input and output voltages are 5 V and 3.3 V, respectively. Furthermore, 61% efficiency maintains under 20 mA load current, which is higher than the traditional converters.