Digital control of Single-Inductor Multiple-Output step-down dc-dc converters in CCM

This paper investigates the application of digital control for non-isolated single-inductor multiple-output step-down dc-dc converters operating in continuous-conduction mode. The accurate and independent control of each output requires a sophisticated digital control architecture so as to minimize the cross-regulation problem. The adopted control includes a separate regulation for common-mode and differential-mode output voltages. Due to the differential-mode control loop dependence on the load current, a variable-gain functional block has been investigated; this provision keeps the differential-mode loop gain constant under different load conditions. Moreover, a nonlinear evaluation of the common-mode voltage has been investigated in order to improve the system dynamic response to asymmetrical load changes. Even if aimed at an integrated solution, experimental verifications have been performed using discrete components, implementing the digital control in a field-programmable gate array. Simulation results on a three-output converter and experimental results on dual-output converter (Vin = 2.5 4divide5 V, Vo1 = Vo2 = 0.9divide1.5 V, and Ioperp = Io2 = 0 4divide0.6 A) confirm the proposed analysis.