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
L
) ripple, which is the AC component $(\Delta \mathrm{I}_{L})$ of i
L
, by additionally using a flying capacitor (C
F
). However, this converter is not effective in reducing power loss in recent devices that require a large load current (I
LOAD
), because a large DC $\mathrm{i}_{L}(\mathrm{I}_{L,DC})$ passes through a single L, which causes a large power loss from the DC resistance (R
DCR
) of the L. A hybrid converter reduces the power loss by reducing both $\mathrm{I}_{L,DC}$ and $\Delta \mathrm{I}_{L}$ owing to $\mathrm{aC}_{F}$ that distributes $\mathrm{I}_{LOAD}\,$ [3] because the power loss occurring in the R
DCR
is proportional to the square of $\mathrm{I}_{L,DC}$. However, this converter cannot avoid a hard switching operation when the C
F
transfers the charge to the output (V
OUT
), which causes a noise issue in the system. A multi-phase converter distributes the I
LOAD
by using an additional L instead of the C
F
, and thus, it reduces the power loss without the hard switching operation [4]. However, if the Ls have unbalanced $\mathrm{i}_{L}\mathrm{s}$, the power loss cannot be effectively reduced. Therefore, this converter requires a complicated technique for balancing $\mathrm{i}_{L}\mathrm{s}$. On the other hand, a double step-down (DSD) converter [5] distributes the I
LOAD
through two Ls with $\mathrm{aC}_{F}$. The DSD converter is practical because it naturally balances the $\mathrm{i}_{L}\mathrm{s}$ owing to the topology itself and reduces both $\mathrm{I}_{L,DC}$ and $\Delta \mathrm{I}_{L}$, 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
F
and two switches are additionally used as in C
F
-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.