A 93.3% peak-efficiency self-resonant hybrid-switched-capacitor LED driver in 0.18-μm CMOS technology

This paper presents an integrated light-emitting diode (LED) driver based on a self-resonant hybrid-switched-capacitor converter (H-SCC) operating in the megahertz range. An integrated zero-current detection (ZCD) circuit is designed to enable self-resonant operation and zero-current switching. A self-resonant timer is proposed to set the switching frequency to resonance automatically, accommodating for variations in the LED voltage, output current, inductor value, and/or parasitic components, and improving the converter efficiency at light loads without the need for an accurate clock with variable frequency. A ZCD threshold control is also proposed to enable continuous conduction mode and improve efficiency at large currents. The design of high-speed integrated current sensors to measure the inductor current in the H-SCC is also presented. Capacitors, power switches, ZCD, current monitors, and the control circuitry of the LED driver are integrated on-chip in a low-cost, 5-V, 0.18-μm bulk CMOS technology. The proposed driver was measured using inductor values between 36 and 470 nH. It achieves a peak efficiency of 93.3% and an efficiency of 83.1% at the nominal current. The LED driver is able to control a 700-mA LED down to less than 10% of its nominal current. The effective chip area is 7.5 mm ², and the maximum power density is 373 mW/mm ². To our knowledge, this LED driver can achieve efficiencies comparable to prior art LED drivers using a 6.6 × smaller inductor.