A SIMO Parallel-String Driver IC for Dimmable LED Backlighting With Local Bus Voltage Optimization and Single Time-Shared Regulation Loop

Traditional LED drivers with multiple converters for powering up multiple strings in parallel suffer from high system volume and cost. The reported literature with single converter and dynamic bus voltage offers compact designs. However, the performance on power consumption is degraded. Meanwhile, all the aforementioned approaches require multiple current regulation elements, which inflict current balance errors due to mismatches. A compact single-inductor multiple-output parallel-string LED driver with time-multiplexing control is, thus, proposed. It can independently optimize local bus voltages for power loss reduction. In addition, a single time-shared control loop is proposed for current regulation in multiple parallel strings, resulting in a dramatic reduction of current balance errors. A 0.35 μm CMOS prototype achieves 2.8 times loss reduction over the reported literature, with a current balance error well controlled below 1.7%. The control scheme also offers flexible dimming for advanced backlighting operations.