A 0.18μm CMOS 91%-efficiency 0.1-to-2A scalable buck-boost DC-DC converter for LED drivers

Several emerging portable applications require high-efficiency LED drivers [1-4]. An LED driver is basically a current source that forces the current required for achieving the desired light emission into the LED. In order to increase the LED driver efficiency, besides controlling the LED current, it is necessary to regulate the voltage applied to the LED itself, to minimize the voltage drop across the driver current source and, hence, the power consumption. Depending on the kind of LED and on the current forced through the LED itself (0.1 to 2A in this design) and, hence, on the desired light emission, the voltage required to drive the LED, while maintaining the voltage headroom across the driver current source to the minimum, varies over a wide range (0 to 5V). Starting from a standard voltage supply in the range 2.7 to 5.5V, a buck-boost DC-DC converter is then required (Fig. 16.4.1). The buck-boost DC-DC converter includes the LED in the control feedback loop and has to provide fast turn-on and load transients (on the order of 20μs), in order to allow pulsed operation of the LED itself.