A 98.5% Peak Efficiency 2/3-Phase Buck-or-Boost Converter With VCR-Independent Loss Optimization and Unconditional RHP Zero Elimination Achieving 2.76A/mm2-Current-Density and 6.5µs Recovery

Buck-boost converter is commonly used in portable electronics to regulate a standard supply of 3.4V or 5V from a 2.7-4.2-V Li-ion battery voltage, or to charge the battery from a 5-V bus, typically demanding high conversion efficiency, high current density, and fast transient response as shown in the top-left of Fig. 1. Traditional buck-boost structure suffers from large inductor DC current $(l_{\mathrm{L}},\text{DC})$ and right-half-plan (RHP) zero in boost mode, resulting in compromised performances. Recent works using flying capacitor $(C_{F})$ -assisted technique to reduce $l_{\mathrm{L}, DC}$ or remove RHP zero can be topologically divided into two types: inductor-at-output (IAO) [1]–[5] and multi-path-based [6]–[10]. IAO structure performs like a buck converter and eliminates the RHP zero, as well as reducing $l_{\mathrm{L}, DC}$ in boost mode. However, since the converter operates in buck mode, e.g., 3. $8\sim 3.5\mathrm{V}$ to 3.4V, for most of the power life $>$ 60%) of a Li-ion battery, IAO converters suffer from significant inductor DC resistance (DCR) loss. Multi-path-based structures use CF to reduce $l_{\mathrm{L}, DC}$ and can relieve the above issue in buck mode [6]–[8]. Nevertheless, their $l_{\mathrm{L}, DC}$ reduction effectiveness is weaken as input voltage $(V_{\text{IN}})$ drops close to the output voltage $(V_{0})$. This is not friendly to Li-ion battery power management as the majority power cycle asks for a voltage conversion ratio (VCR) slightly larger than 1. Besides, in some cases, RHP zero exists due to the discontinuity of inductor current $(l_{\mathrm{L}})$ to output [6], or the reduced amount of charge delivered to output by CF when the inductor energizing phase is prolonged [7], [8]. Although multi-path structures with more CF obtains better $l_{L, DC}$ reduction [9], [10], more power switches in series increases their conduction and switching losses. Further, the common existence of RHP zero degrades phase margin or limits loop bandwidth, leading to a long recovery time $(T_{\mathrm{R}})$ [6]–[8] or stability issue [9] under load steps. Besides, prior hybrid buck-boost converters also suffer from suboptimal conduction loss $(\mathrm{P}_{\text{Con}})$ property when VCR changes, as both $;_{\mathrm{L}, DC}$ and CF current $(l_{\text{CF}})$ are VCR (equivalently duty ratio $(D)$) dependent. Although constant $l_{\mathrm{L},DC}$ reduction and inrush $l_{\text{CF}}$ elimination techniques have been reported [11], [12], the total $\mathrm{p}_{\text{con}}$ is still VCR dependent and can turn to a suboptimal level.