A 5V Input 98.4% Peak Efficiency Reconfigurable Capacitive-Sigma Converter With Greater than 90% Peak Efficiency for the Entire 0.4~1.2V Output Range

Abstract

For the battery- or USB-powered portable smart devices, which supply their computing cores with a wide-range sub-volt rail, the energy-efficient high and wide voltage-conversion-ratio (VCR) converters are crucially important. In addition, low form factor and decent transient responses are also favorable for such applications. Prior state-of-the-art designs either use single-stage hybrid designs using multi-level or Dickson converters [1 – 3], or adopt two-stage cascaded architectures with a highly efficient unregulated front (or rear) stage [4], as shown in Fig. 18.6.1 (left). The multi-level designs, which conduct the full inductor current through all the on-state switches, are suited to low-to-medium power levels with limited current density. The Dickson converters take advantage of a high conversion ratio, however, at the cost of reduced output voltage range. The two-stage designs which show decent output range and efficiency, however, can suffer from heavy load efficiency degradation considering that the efficiency of both stages degrade with increasing load and the overall efficiency which is the product of the efficiencies of the two stages is severely degraded. Inspired by the inductive-sigma converter [5] which shunts a highly efficient unregulated LLC with a regulated Buck, this work proposes a reconfigurable capacitive-sigma converter. By input-series and output-shunting a highly efficient unregulated switched-capacitor (SC) converter with a reconfigurable Dickson hybrid Buck stage, the power stage input current is reused and output currents are combined. Therefore, the overall efficiency is greatly improved in a wide continuous VCR range and with an enhanced loading capacity. Besides, as will be demonstrated, the proposed design shows inherently decent load transient and regulation performances.