Reduced-switch SCALDO technique for high-current VRM implementation

A supercapacitor-assisted low-dropout regulator (SCALDO) technique has been developed previously to improve the end-to-end efficiency of linear regulators based on low-dropout regulators. To implement this technique in a high-current application such as a voltage regulator module (VRM), it is necessary to reduce the number of low-speed switches used in SCALDO topologies. A preliminary prototype of a modified SCALDO version has been built with commercially available low-dropout regulators to prove the concept of reduced-switch SCALDO. One limitation of this reduced-switch SCALDO prototype was the unwanted discharge of supercapacitors via body-diode of low-dropout regulators. Experimental results indicate that the reduced-switch SCALDO can be further developed for application to VRM by suitably designing a high-current low-dropout regulator. This paper presents the theoretical aspects of the reduced-switch topology, a new approach to avoid the low-dropout regulator body-diode effect on supercapacitors, and a method to optimize the control circuits. The preliminary results of a custom-designed 1.5 V, 2 A discrete low-dropout regulator and a 3.5-to-1.5 V reduced-switch SCALDO converter are presented.