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In this work, a multi-independent-output, multi-string, high-efficiency, boost-converter-based white LED (WLED) driver architecture is proposed. It utilizes a single inductor main switch with a common maximum duty cycle controller (MDCC) in the feedback loop. A simple pulse skipping controller (PSC) is utilized in each high-side switch of the multiple independent outputs. Despite the presence of multiple independent outputs, a single over-voltage protection (OVP) circuit is used at the output to protect the circuit from any voltage above 27 V. An open circuit in any of the strings is addressed, in addition to the LED’s short-circuit conditions. Excellent current matching between strings is achieved, despite the low ON-resistance (Rdson) of transistors used in the 40 nm process. Most circuits are designed in digital CMOS logic to overcome the extreme process variations in the 40 nm node. Compared to a single output parallel strings topology, a 50% improvement in efficiency is achieved relative to extremely unbalanced strings. Three strings are used in this proposal, but more strings can be supported with the same topology. Each string is driven by a 25 mA current sink. An input voltage of 3.2–4.2 V and an output voltage up to 27 V are supported.

This work presents various essential features and design aspects of a single-inductor, common-output, and multi-string White Light Emitting Diode (WLED) driver for low-power portable devices. High efficiency is one of the main features of such a device. Here, the efficiency improvement is achieved by selecting the proper arrangement of WLEDs and a proper sensing-circuit technique to determine the minimum, real-time, needed output voltage. This minimum voltage necessary to activate all WLEDs depends on the number of strings and the forward voltage drops among the WLEDs. Advanced CMOS technology is advantageous in mixed-signal environments such as WLED drivers. However, this process suffers from low on-resistance, which degrades the accuracy of the current sinks. To accommodate the above features and mitigate the low node process issue, a boost-converter that is single output with a load of a three-string arrangement, with 6 WLEDs each, is presented. The designed driver has an input voltage range of 3.2–4.2V. The proposed solution is realized with ultra-low power consumption circuits and verified using ADS tools utilizing 40 nm 1P9M TSMC CMOS technology. An inter-string current accuracy of 0.2% and peak efficiency of 91% are achieved with an output voltage up to 25 V. The integrated WLED driver circuitry enables a high switching frequency of 1MHz and reduces the passive elements’ size in the power stage.