A multiple-output switched-capacitor DC-DC converter for individual brightness control of RGB LEDs with time-interleaved control and output current regulation

Abstract

In this paper, an integrated multiple-output switched-capacitor (SC) converter with time-interleaved control and output current regulation is presented. The SC converter can reduce the number of passive components and die areas by using only one flying capacitor and by sharing active devices. The proposed converter has three outputs for individual brightness control of red-green-blue (RGB) LEDs. Each output directly regulates the current due to the V-I characteristics of LEDs, which are sensitive to PVT variations. In the proposed converter, the current-sensing technique is used to control the output current, instead of current-regulation elements (resistors or linear regulators). Additionally, in order to reduce the active area, three outputs share one current-sensing circuit. In order to improve the sensing accuracy, bias current compensation is applied to a current-sensing circuit. The proposed converter has been fabricated with a CMOS 0.13-mu m 1P6M CMOS process. The input voltage range of the converter is 2.5-3.3 V, and the switching frequency is 200 kHz. The peak power efficiency reaches 71.8 % at V (IN) =2.5 V, I (LED1) = 10 mA, I (LED2) = 18 mA, and I (LED3) = 20 mA. The current variations of individual outputs at different supply voltages are less than 0.89, 0.72, and 0.63 %, respectively.