Programmable output switched capacitor step-down DC-DC converter with high accuracy using Sigma-Delta Feedback Control Loop

This paper describes the CMOS implementation of variable output voltage, multiphase switched capacitor step-down DC-DC converter with a large number of target voltages using Sigma-Delta Feedback Control Loop. The number of target voltages generated using n-flying capacitors are of the order of 2n. Expressions for equivalent series resistance Req, conduction, switching power loss and efficiency are obtained and compared with the spice simulation results. The Sigma-Delta Feedback Control Loop is designed which automatically switch between various target voltages and simulated in Cadence Analog-Mixed Signal flow. The Sigma-Delta feedback controller has a very high gain at DC and hence gives higher accuracy as compared to alternative methods. The 3/4 step-down converter circuit is described and analyzed by varying switching frequency and load for different values of bottom plate parasitic capacitance. An efficiency of about 77.3% is achieved with 10% bottom plate parasitic capacitance for a load current of 135 uA and input voltage of 1.8 V at 2 MHz of switching frequency. The load regulation of 7.33 mV/mA and line regulation of 6.5 mV/V is achieved.