13-2 zyxwvut A 1.8V Single-Inductor Dual-Output Switching Converter for Power Reduction Techniques zyxw Dongsheng Ma, Wing-Hung Ki, Chi-Ying Tsui and Philip K.T. Mok Integrated Power Electronics Laboratory Department of Electrical and Electronic Engineering The Hong Kong University of Science and Technology Clear Water Bay, Hong Kong SAR, China Tel: (852) 2358-8535 Fax: (852) 2358-1485 Email: eemds@ee.ust.hk Abstract A 1.8V integrated single-inductor dual-output boost converter is presented. This converter adopts a time- multiplexing control in providing two independent supply voltages using only one lpH off-chip inductor. The topology could easily be extended to give multiple outputs. The converter is fabricated with a standard 0.5pm CMOS n-well process. At an oscillator frequency of 1 MHz, the conversion efficiency reaches 88% at a total output power of 350mW. multiplexing (TM) control, a single controller is shared by all the outputs. Synchronous rectification, in the sense that the transistor in replacing the diode is switched off when the inductor current tends to go negative, is employed, thus eliminating diode drops and enhancing efficiency. All power switches are fabricated on-chip and with only one inductor for two outputs, off-chip components are minimized. Other features include modified current sensing technique and ringing suppression technique, to be discussed in due course. zyx II. SIMO Converter Architecture and Control Strategy I. Introduction For a digital signal processor, high speed computation requires a high supply voltage vdd for fast switching. Since power consumption is proportional to the square of zyxwvuts V, it is advisable to lower vdd when the computation speed could be reduced. Supply voltage scheduling using multiple or variable supply voltage schemes [I-51 are thus desirable in optimizing the power and speed of switching systems. A critical issue in implementing such a power management system is to generate multiple power supply voltages efficiently. Conventional solutions may use several independent converters or employ a transformer with multiple secondary windings to deliver energy into the various outputs [6,7]. The first method is not preferred because it requires too many components (controllers and power devices). The second method may suffer serious problems arise from cross regulation. A multiple-output converter with multiple inductors is reported in [5] recently. Because existing monolithic magnetic technology cannot fabricate inductors of suitable values and quality for efficient power transmission, inductors remain as off-chip components. As the number of outputs increases, the number of inductors increases accordingly, which is not preferable for portable applications. Furthermore, the topology in [5] limits to step-down conversion and only voltages lower than the power supply could be generated. If no high supply voltage is available, the system may not fulfill optimization tasks [3], because part of the system may have high speed requirements. Moreover, to work at low voltages, sophisticated analog circuits are needed, which are not easy to design. Hence, a boost converter is more favorable to power high-speed processor cores with a very low supply voltage. In this work, we introduce a single-inductor multiple-output (SJMO) boost converter topology. By employing time Fig. 1 shows the power stage of the proposed single- inductor dual-output (SIDO) boost converter. The two outputs Vo, and Vob share the inductor L and the switch SI. Fig. 2 shows the timing of the converter. It works with two complementary phases $a and 4. During Qa = 1, Sb is opened and no current flows into Vob, while SI is closed first. The inductor current IL increases until DlaT expires (determined by the output of an error amplifier), where T is the switching L zyxwvut r"""ipo p Fig. 1 Power stage of the SIDO converter . . . . . . . . . : :wit : : : : : :H n . . . S. ;-n= . . . . . . . . . . . . . . . . . . . . . Fig. 2 Timing diagram of the SIDO converter 137 4-891 14-014-3/01 2001 Symposium on VLSl Circuits Digest of Technical Papers