A Single-Inductor Multiple-Output (SIMO) DC-DC Converter with Wide Operating Voltage Range for Mobile Devices

Abstract

As use of mobile devices has continuously increased, various researches to extend the operating time of mobile device have been carried out [13-15]. They are mainly focused on the low power operation in the application block, increase of battery capacity, and performance improvement of the power management block. Among the above solutions, improvement of power efficiency and extension of operating voltage range of the power management block are the most effective solutions to prolong the operating time without adding the cost or sacrificing the performance. In the power management block of mobile devices, there are two types of voltage regulators: one is low drop-out (LDO) linear regulator, and the other is switched mode power converter. In the case of the LDO linear regulator, additional components are required less and fabrication cost is low. However, the power efficiency is relatively low because the power is continually dissipated on the pass transistor. On the other hand, the switched mode power converter has high power efficiency because the power is transferred from input to output, using the inductor without power loss in the ideal case. However, the size and cost are increased because an inductor, a basic component in the switched mode power converter, requires a large form factor and high cost. To secure high power efficiency, low cost, and a low form factor, the single-inductor multiple-output (SIMO) DC-DC converter has been researched [3-7]. In SIMO DC-DC converter, only one inductor is used to make multiple outputs so that the size and cost of the mobile device are considerably decreased. However, changes in load current at one output affect not only the regulated voltage of the output but that of the other outputs as well because all outputs share a common inductor. The operating voltage range of the power management block in mobile devices is limited by the operating guideline to guarantee reliable operations. In particular, it is strictly regulated because output voltage of Li-ion battery is decreased according to operation. In order to extend the operating voltage range, reliable output voltages should be generated in the power management block when the output voltage of battery is lowered. This thesis proposes a SIMO DC-DC converter to attain high power efficiency, low interference by other outputs, and a wide operating voltage range. The proposed SIMO DC-DC converter was simulated by using a 0.18 µm CMOS process technology with high voltage devices of 5 V. Simulation results show that the proposed SIMO DC-DC converter has maximum power efficiency of 92.4%, and that the average fluctuation of output voltage decreases from 90 mV to 45 mV when load current at the first output is changed as 100 mA. At the same time, the minimum voltage of operating voltage range decreases from 3.3 V to 3.0 V. These findings demonstrate that the proposed SIMO DC-DC converter is well suited to the power management block in mobile devices.