FPGA control of SIMO DC-DC converters using load current estimation

This paper investigates a digital control for non-isolated single-inductor multiple output (SIMO) step-down DC-DC converters using load current estimation. The proposed control architecture has been applied for SIMO converters operating in continuous conduction mode (CCM), where there is a cross-regulation issue between output voltages. The adopted control includes a separate regulation of the common-mode and the generalised differential-mode output voltages for the input half-bridge and for the output switches respectively. Due to the differential-mode control loop dependence on the load current, an inductor current estimation is used to perform a variable gain for the differential-mode regulation. Moreover, a non-linear evaluation of the common-mode voltage have been investigated in order to improve the system dynamic response at different load conditions. Even if aimed to an integrated solution, experimental investigation has been performed using discrete components, implementing the digital control in a field programmable gate array (FPGA). Simulation results on a three output converter and experimental results on dual output converter (V_in=2.5÷5 V, V_o1=V_o2=0.9÷5 V, I_o1=I_o2=0÷0.6 A) confirm the proposed analysis.