A novel control technique for single-inductor multiple-output DC-DC buck converters

This paper presents the design of a single-inductor regulated multiple-output (SIMO) buck converter with interleaved switched capacitor outputs. A small signal analysis of the buck converter using state space averaging technique is carried out. A compensating network and novel control logic are designed to minimize effects of cross regulation and load transient in the three-coupled outputs. In view of the significant advantages of current-mode control over voltage-mode the main switch of this multiple-output converter is made current-controlled. Interestingly, sub-harmonic oscillations start occurring at a much lower duty cycle than 0.5 in multiple-output current controlled converters. Our work focuses on the cause of instability and the minimum duty ratio beyond which sub-harmonic oscillations occur. Lastly, the expression of a slope-compensating ramp, required to eliminate sub-harmonic oscillations, has been derived for multiple-output converters. The transistor level design of the above has been designed and simulated in Cadence Analog Environment in a 0.5u process. The simulation results are in conformity with the evaluated stabilizing ramp to eliminate sub-harmonic oscillations.