A Single-Duty-Cycled Buck-Boost Converter Achieving Low Output Ripple and Seamless Mode Transition

This article presents a single-duty-cycled buck-boost (SDC-BB) converter designed to power mobile organic light-emitting diode (OLED) displays featuring a wide dynamic range (WDR). Traditional BB converters often suffer from significant output ripples and voltage spikes, which this work aims to address by employing an inductor-last topology combined with a multilevel switched-capacitor (SC) stage. Previous strategies (both single- and multi-mode) for controlling the SC stage have resulted in either increased output voltage $(V_{\text {O}})$ ripples or non-smooth transitions between buck and boost modes, leading to $V_{\text {O}}$ fluctuations during mode changes. To overcome these shortcomings, we propose a control technique that seamlessly covers both buck and boost conversions with a single duty cycle (D) while maintaining a lower output ripple. In this work, the flying capacitor, employed in the SC stage, is reutilized for driving the power switches, thereby eliminating the bootstrap overhead. In addition, an adaptive ramp generator is incorporated to ensure immunity to time-division multiple access (TDMA) noise for mobile applications. The SDC-BB converter, fabricated using a 180-nm CMOS process, achieved an output ripple of less than 2.1 mV with a peak efficiency of 96.6%, using a 4.7- $\mu $ H inductor, a 10- $\mu $ F output capacitor, and a 1-MHz switching frequency. Furthermore, it demonstrated output fluctuations within 2.1 mV during transitions between buck and boost modes and verified immunity to TDMA noise with a transient ${\Delta } {V_{\text {O}}}$ of 5.8 mV under a 0.5-V input voltage change over $20~{\mu }$ s.