9.11 A 98.3%-Peak-Efficiency Single-Mode Hybrid Buck-Boost Converter with 7mV Maximum Output Ripple for Li-Ion Battery Management

Hybrid buck-boost converters have been extensively studied for their ability to efficiently convert varying battery voltages (e.g., 2.8V to 4.2V) to a stable mid-3V output in Li-ion battery-powered mobile devices. These converters typically employ either multi-mode or single-mode control as shown in Fig. 9.11.1. Multi-mode buck-boost converters reconfigure the power stage to operate in buck, boost or transition mode based on the battery voltage level $(\mathrm{V}_{\text{IN}})$. Compared with the conventional buck-boost converter (CBBC), such hybrid topologies using flying capacitor $(\mathrm{C}_{\mathrm{F}})$ reduce the number of power switches or their voltage stress in the current path, thereby lowering the conduction loss. Dual-path techniques can also be employed to further reduce inductor current for efficiency improvement [3]. However, these converters often face mode-transition issues. For example, in [2], [3], discontinuous voltage across the $\mathrm{c}_{\mathrm{F}}$ during mode transitions causes large inrush currents and output voltage glitches. Similarly, in [4]–[6], changes in duty cycle during transitions lead to output voltage overshoot. To avoid mode-transition issues, single-mode topologies that cascade a boost and a buck bridge have been proposed [7]–[10]. However, these designs suffer from reduced efficiency due to the increased number or voltage stress of the power switches, and the discontinuous output current delivery leads to large voltage ripple.