4.3 An 87%-peak-efficiency DVS-capable single-inductor 4-output DC-DC buck converter with ripple-based adaptive off-time control

Improving battery longevity in portable devices usually requires the use of different voltage levels with a wide range of load capability for various functional blocks. Since a single-inductor-multiple-output (SIMO) converter can support multiple output voltages while using only one inductor, it is an excellent candidate to minimize the component count and thus the production cost. However, the cross-regulation and power consumption are two main issues of the previously reported SIMO converters [1-5]. Although pseudo-continuous conduction-mode (PCCM) control with a freewheel period [1] tries to augment power density and eliminate cross-regulation, associated power dissipation of freewheel switch exacerbates its overall efficiency. The charge-control technique with energy recovery presented [2] decouples the output channels between each switching cycle, at the expense of additional switching loss and slow response. The comparator-based controlled SIMO converters are investigated in [3, 4] and the cross-regulation in most channels is improved due to the fast response of the comparator. However, since the channel that is last connected to inductor is inevitably regulated by the accumulative error of all channels to balance the overall inductor current, every load transition at other outputs will introduce serious cross-regulation [3] and load-regulation problem [4] in the channel. In addition, cross-regulation and slow response also limit the application of dynamic voltage scaling (DVS) technique, which is widely used in single-output converters to improve the system power efficiency by providing variable voltage with fast reference tracking.