A 96.5% Efficiency Hybrid Step-Up Converter With Low Input-Level Voltage Stress and Duty-Independent Constant Inductor Current

This article presents a duty-independent step-up converter (DIUC) for battery-powered or USB-powered devices. The DIUC limits the voltage stress on all switches to an input voltage (V _IN) level, eliminating the need for high-voltage (HV) transistors like LDMOS. Unlike previous step-up converters where the inductor current (I_L ) rapidly increases as a duty (D) rises, the DIUC maintains I_L equal to the load current regardless of D. This feature mitigates the conduction loss due to the inductor parasitic dc resistance (DCR) and right-half-plane (RHP) zero effect, improving both power efficiency and frequency response. When changing the operation mode according to the conversion ratio (CR), the DIUC achieves a small overshoot of 158 mV and undershoot of 107 mV in the output voltage (V _OUT) with the proposed smooth mode transition (SMT) technique. Additionally, a multi-step gate driving method with two precharging techniques reduces the required bootstrap capacitance by 46.3% to save the silicon area. The 0.18- $\mu $ m prototype chip uses only 5-V CMOS transistors, while all bootstrap capacitors are integrated on the chip. With a 4.7- $\mu $ H inductor (DCR of 98 m $\Omega $ ) and two 10- $\mu $ F flying capacitors, the DIUC achieves high ${V} {_{\text {OUT}}}$ up to 13 V, a maximum load current of 1.2 A, and a peak efficiency of 96.5%.