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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(l_{\mathrm{L}},\text{DC})$</tex> and right-half-plan (RHP) zero in boost mode, resulting in compromised performances. Recent works using flying capacitor <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(C_{F})$</tex> -assisted technique to reduce <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$l_{\mathrm{L}, DC}$</tex> 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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$l_{\mathrm{L}, DC}$</tex> in boost mode. However, since the converter operates in buck mode, e.g., 3. <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$8\sim 3.5\mathrm{V}$</tex> to 3.4V, for most of the power life <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$&gt;$</tex> 60%) of a Li-ion battery, IAO converters suffer from significant inductor DC resistance (DCR) loss. Multi-path-based structures use CF to reduce <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$l_{\mathrm{L}, DC}$</tex> and can relieve the above issue in buck mode [6]–[8]. Nevertheless, their <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$l_{\mathrm{L}, DC}$</tex> reduction effectiveness is weaken as input voltage <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(V_{\text{IN}})$</tex> drops close to the output voltage <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(V_{0})$</tex>. 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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(l_{\mathrm{L}})$</tex> 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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$l_{L, DC}$</tex> 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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(T_{\mathrm{R}})$</tex> [6]–[8] or stability issue [9] under load steps. Besides, prior hybrid buck-boost converters also suffer from suboptimal conduction loss <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\mathrm{P}_{\text{Con}})$</tex> property when VCR changes, as both <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$;_{\mathrm{L}, DC}$</tex> and CF current <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(l_{\text{CF}})$</tex> are VCR (equivalently duty ratio <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(D)$</tex>) dependent. Although constant <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$l_{\mathrm{L},DC}$</tex> reduction and inrush <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$l_{\text{CF}}$</tex> elimination techniques have been reported [11], [12], the total <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{p}_{\text{con}}$</tex> is still VCR dependent and can turn to a suboptimal level.