8.8 A 97.18% Peak-Efficiency Asymmetrically Implemented Dual-phase (AID) Converter with a full Voltage-Conversion Ratio (VCR) between 0-and-1

As portable and wearable devices are getting smaller and need to achieve a higher performance, a DC-DC converter using a small-size inductor (L) has become necessary. Accordingly, as shown in Fig. 8.8.1, previous researches have suggested various methods to achieve high efficiency with a small size L. Among them, 3-level converters [1, 2] reduce the power loss by reducing the inductor current (i <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</inf> ) ripple, which is the AC component (Δ IL) of i <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</inf> , by additionally using a flying capacitor (C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</inf> ). However, this converter is not effective in reducing power loss in recent devices that require a large load current (I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LOAD</inf> ), because a large DC iL(IL,DC) passes through a single L, which causes a large power loss from the DC resistance (R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DCR</inf> ) of the L. A hybrid converter reduces the power loss by reducing both IL,DC and Δ IL owing to aCF that distributes ILOAD\, [3] because the power loss occurring in the R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DCR</inf> is proportional to the square of IL,DC. However, this converter cannot avoid a hard switching operation when the C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</inf> transfers the charge to the output (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OUT</inf> ), which causes a noise issue in the system. A multi-phase converter distributes the I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LOAD</inf> by using an additional L instead of the C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</inf> , and thus, it reduces the power loss without the hard switching operation [4]. However, if the Ls have unbalanced iLs, the power loss cannot be effectively reduced. Therefore, this converter requires a complicated technique for balancing iLs. On the other hand, a double step-down (DSD) converter [5] distributes the I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LOAD</inf> through two Ls with aCF. The DSD converter is practical because it naturally balances the iLs owing to the topology itself and reduces both IL,DC and Δ IL, which results in high efficiency. However, the DSD converter has a limited voltage conversion ratio (VCR) between 0 and 0.25. The VCR can be extended beyond the DSD converter if one C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</inf> and two switches are additionally used as in C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</inf> -cross-connected (CCC) converter [6]; however, it still has a limited VCR of between 0 and 0.5. As a result, the DSD and CCC converters can only be used in limited applications.