Abstract
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.
Highlights
By examining modern smart portable devices, one can find plenty of voltage domains which intended to serve different modules and sub-modules inside those devices [1,2]
The white LED (WLED) driver ideally operates in a similar manner to a voltage-regulated boost converter, except it regulates the output current through the string of LEDs with high power efficiency, especially in portable devices
Signal indicates the mode of operation (MDCC or pulse skipping controller (PSC)) the WLED driver has at any time
Summary
By examining modern smart portable devices, one can find plenty of voltage domains which intended to serve different modules and sub-modules inside those devices [1,2]. The WLED driver ideally operates in a similar manner to a voltage-regulated boost converter, except it regulates the output current through the string of LEDs with high power efficiency, especially in portable devices. To overcome the disadvantages above of the typical architecture, multiple independent output WLED drivers are becoming the mainstream topology [12,13] This comes with a potentially higher number of switches per string, more complex control circuitry, and multiple circuits (one per output) for common features such as over-voltage protection (OVP). A minimum number of switches per string, and a simple and common controller, excellent current matching among strings is achieved This solution requires a single OVP circuit for all independent outputs.
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