Design and Implementation of a Sliding-Mode Controller for Low-Dropout/Linear Regulator

This brief presents an approach to utilize of sliding-mode (SM) controller in digital low-dropout/linear regulators. Various design aspects, including the extraction of the regulator state-space model and sliding coefficients by considering the hitting, existence, and stability conditions are described. Moreover, the freeze control block is introduced as a solution to compensate for the high frequency chattering phenomenon of SM, resulting in reduction of switching losses. In order to verify the statements, a quasi digital low-dropout/linear regulator is implemented in a discrete form on a PCB. The circuit consists of the proposed current-mode current feedback amplifier-based SM controller and switched-mode pMOS array driven by a bidirectional serial shift register, which is controlled by the SM controller. The results reveal that the controller detects the load changes rapidly, and eliminates the output limit-cycle oscillation, providing a robust and stable output voltage.