An LDO regulated DC-DC converter with voltage ripple suppression and adaptive dropout voltage control

Abstract

This paper presents a low dropout regulator (LDO) regulated DC-DC converter with suppressed voltage ripple and enhanced light load efficiency. In this proposed hybrid system, an adaptive dropout technique, where DC-DC converter takes the gate of LDO's power transistor as the feedback point to combine DC-DC converter and LDO in one control loop, is adopted to make LDO's dropout voltage adaptive to load current rather than fixed value. Owing to the cascaded LDO and the adaptive dropout technique, the hybrid system obtains a small voltage ripple with improved overall efficiency, especially in light load. The chip was implemented in 130 nm CMOS process. The voltage ripple is reduced to 3 mV at the load current of 40 mA. The overall efficiency of the proposed hybrid system is 60.74% in 30 mA light load and is improved by 15.6% compared with conventional fixed dropout voltage architecture.

A novel DC-DC converter and LDO cascaded circuit with improved dynamic response and loop stability

“…The efficiency of DC-DC converters can reach more than 90% [1,2,3,4,5,6,7,8,9]. However, its large output ripple limits its applications in sensitive electronic load where additional LDO is required to achieve low power noise and ripple [10,11,12,13,14,15,16,17,18,19]. Hybrid methods of switched-mode, switched-capacitor-mode DC-DC, low dropout voltage regulator (LDO) are proposed in recent years [20,21,22,23,24].…”

“…However, since the loop characteristics of the LDO are added to the feedback loop of the DC-DC converter, the two-loop characteristics become more complex which requires complicated loop compensation. Other papers such as [28,30] also proposed the methods of adaptive change of the dropout voltage. Although the zero/pole of the LDO is avoided to be brought into the DC-DC converter loop, these dropout voltage adjustment methods are not the most efficient for the gate voltage of the LDO's pass element is not detected directly.…”