A novel 4-to-3 step-down on-chip SC DC-DC converter with reduced bottom-plate loss

Abstract

This paper presents a novel fully integrated on-chip switched-capacitor (SC) DC-DC converter that supports programmable regulated load voltage ranging from 2.6V to 3.2V out of 5V input supply. MOS capacitors are used for flying capacitors (600pF) and load capacitor (400pF) in this implementation. To minimize the bottom-plate parasitic capacitor related loss while maximizing the load current driving capability, the proposed 4-to-3 step-down topology utilizes two differently sized conventional 2-to-1 step-down topologies, each of which has different value of flying capacitor. In addition, the proposed implementation reduces switching loss and control circuit loss since the internally generated output voltage of the bottom 2-to-1 block is used as the supply for the control circuits throughout the small internal LDO regulator. The proposed converter is designed and simulated using high-voltage 0.35 μm BCDMOS technology. The programmable output voltage is regulated by means of pulse frequency modulation (PFM) technique using 18-bit shift register and digitally controlled oscillator (DCO). The proposed switched-capacitor converter achieves the peak efficiency of 72% while it delivers the load current between 1mA and 10mA. 10-phase interleaving technique enables the output voltage ripple of the load voltage to be less than 1%.