Multi-Channel LED Driver with Accurate Current Matching for Portable Applications

In this paper, we present a multi-string LED driver based on a current-limiting hysteretic boost converter, which is capable of driving ten LEDs in five parallel strings. An accurate current matching circuit with low voltage headroom requirement is implemented to match currents in all LED strings. Dynamic compensation of the LED forward voltage mismatch between the strings is achieved with the introduction of a minimum voltage selector block. A PFM dimming circuit is designed to operate with a 200 kHz clock and has 11 programmable dimming ratios, ranging from 2:1 to 2048:1. This LED driver is implemented in 0.6-μm CMOS process and operates from a Li-ion battery with a voltage range 3 - 4.2 V. It is suitable for backlight LED displays in mobile devices.