8.6 A Fully Integrated 85%-Peak-Efficiency Hybrid Multi Ratio Resonant DC-DC Converter with 3.0-to-4.5V Input and 500μA -to-120mA Load Range

DC-DC converters for applications like wearables require an ultra-compact and flat module size. Hybrid converters are a promising converter class that supports integration of inductive and capacitive components, while minimizing losses and improving power density. Since many of these applications are often in sleep mode, high efficiency has to be achieved from high to low output power. Fully integrated 3-level buck converters [1, 2] do not maintain good efficiency over the full load range, since they operate at high switching frequencies, required for inductive PWM operation with small inductors. The converter in [3] achieves better efficiencies, but has a small conversion ratio. Resonant SC converters [4, 5] reach high efficiencies due to lower switching frequencies and better passive component utilization. However, low-power operation is not supported [1, 3–5] or it suffers from low efficiencies [2]. Moreover, only [4] supports a wide input voltage range based on mixed inductive and resonant operation, but still has an efficiency drop over varying input voltages. Hybrid converters, combining an SC cell with an external LC output filter, operated with inductive PWM control [6], achieve high efficiencies over wide input voltage, but they do not support low power operation.