The stability issue of the voltage regulators using a ripple-based constant on-time controller with DC offset-correction circuit

In recent years, the ripple-based constant on-time (RBCOT) control scheme for voltage regulators has been adopted in many applications because of its high efficiency feature under light-load conditions. However, a RBCOT control suffers from output-voltage offset problem. Therefore, an offset correction circuit (OC) is often added to the basic RBCOT scheme to correct the problem. In the OC circuit, there is a RC filter. The size of this RC filter not only affects the circuit stability and converter transient responses but also directly affects the controller chip size/cost. The main focus of the present paper is to investigate the relationship between the RC filter value and the feedback stability so that RC value can be minimized while avoiding circuit instability. A time-domain analysis approach is proposed to model OCRBCOT scheme for a buck converter configuration. Experimental and simulation results are given for verification.