Digital Average Current Control Technique for High Performance SIMO-Based Dimmable LED Driving

Abstract

A single-inductor-multi-output (SIMO) DC-DC converter is widely acknowledged as the effective solution as well as commercially used for highly integrated multichannel and multistring dimmable LED driving. However, the requirements of high bandwidth dynamic current tracking and reduced flickering effects remain challenging to satisfy, particularly under frequent circuit reconfigurations with high frequency PWM dimming. This paper proposes a reconfigurable fully digital average current control (DACC) technique along with a feedback voltage controller in a SIMO DC-DC converter, in which both the inductor current and output voltages are sampled using an ADC (with a time-multiplexing manner) once per switching cycle using an event-based sampling mechanism. The proposed technique offers (i) precise average current control, (ii) inherent current-loop stability without ramp compensation, (iii) high current-loop bandwidth, (iv) reduced flickering effects during mode transitions using combined current-source and voltage-source mode configurations, (v) scalability for single-channel, multichannel and multi-string LED driving. Discrete-time small-signal models are derived, and current-loop as well as closed-loop stability analysis is presented along with the controller design. Superior current tracking performance is demonstrated using simulation and experimental results.