Motivated by emerging portable applications that demand ultra-low-power hardware to maximize battery run-time, high-efficiency low-voltage DC-DC conversion is presented as a key low-power enabler. Recent innovations in low-power digital CMOS design have assumed that the supply voltage is a free variable and can be set to any arbitrarily low level with little penalty. This thesis introduces and demonstrates an array of DC-DC converter design techniques which make this assumption more viable. The primary design challenges to high-efficiency low-voltage DC-DC converters are summarized. Design techniques at the power delivery system, individual control system, and circuit levels are described which help meet the stringent requirements imposed by the portable environment. Design equations and closed-form expressions for losses are presented. Special design considerations for the key dynamic voltage scaling enabler, called the dynamic DC-DC converter are given. The focus throughout is on low-power portable applications, where small size, low cost, and high energy efficiency are the primary design objectives. The design

Abstract—The success of wireless sensor networks and their pervasive use is somehow constrained by energy supply which, generally provided by batteries, is a finite resource. Energy har-vesting mechanisms must hence be taken into account to grant a long time operational life, with solar energy being the most inter-esting one in outdoor deployments due to its relatively high power density. In this paper we propose a low-power maximum power point tracker (MPPT) circuit specifically designed for wireless sensor nodes (hence effective, flexible, low cost and power-aware), i.e., a power transferring circuit for optimally conveying solar energy into rechargeable batteries even in not optimal weather conditions. High efficiency is granted by an ad hoc adaptive algorithm which, by keeping the MPPT electronics in its optimal working point, maximizes energy transfer from the solar cell to the batteries. The suggested implementation is particularly effective in critical weather conditions where traditional solutions do not work and is characterized by a flexible enough design for immediately hosting, in a plug in fashion, different solar panels and battery typologies. Index Terms—Adaptive algorithms, maximum power point tracker (MPPT) circuits, power converters, solar energy har-vesting, wireless sensor networks. I.

Abstract—This paper describes design and implementation of a digitally controlled DC-DC converter that provides a dynamically adjustable supply voltage for an RF power amplifier (RFPA). The techniques employed in the design include a combination of constant-frequency continuous conduction mode and a variablefrequency discontinuous conduction mode to achieve very high converter efficiency over a wide range of output power levels. The variable-frequency converter control is accomplished using a simple current-estimator circuit, which eliminates the need for current sensing. An FPGA-based digital controller implementation allows programmability of the mode transition and other controller parameters. In the complete experimental system, which consists of the digitally controlled DC-DC converter and a class-E RFPA operating at 10 GHz, experimental results show that the overall system efficiency is significantly improved over a wide range of RFPA output power levels, e.g. from 22 % to 65 % at a low power level. I.

Abstract { The paper describes a DC-DC converter for use with low voltage microprocessor loads. The control method is a hysteretic current-mode control in the continuous conduction mode which has fast transient response. At light loads, the converter operates in the discontinuous conduction mode using a peak current control method which causes the switching frequency to be proportional to load current, thus maintaining high e ciency in a very wide range of loads. The control method implementation, transient response and output inductor design equations, and equations for designing an input lter to reduce input current di/dt are provided. An inductor current estimator which provides higher e ciency, good transient response, and current limiting, is presented. Experimental results for a 5.0V input, 3.1V output, 13A DC-DC converter are included to verify the theoretical information. 1

Abstract—Integrated switching power supplies with multimode control are gaining popularity in state-of-the-art portable applications like cellular phones, personal digital assistants (PDAs), etc. because of their ability to adapt to various loading conditions and therefore achieve high efficiency over a wide loadcurrent range, which is critical for extended battery life. Constant-frequency, pulse-width modulated (PWM) switching converters, for instance, have poor light-load efficiencies because of higher switching losses while pulse-frequency modulation (PFM) control in discontinuous-conduction mode (DCM) is more efficient at light loads because the switching frequency and associated switching losses are scaled down with load current. This paper presents the design and IC prototype results of an 83 % power efficient 0.5 V, 50 mA CMOS PFM buck (step-down) dc-dc converter with a novel adaptive on-time scheme that generates a 27 mV output ripple voltage from a 1.4-4.2 V input supply (battery-compatible range). The output ripple voltage variation and steady-state accuracy of the proposed supply was 5 mV (22-27 mV) and 0.6 % whereas its constant on-time counterpart was 45 mV (10-55 mV) and 3.6%, respectively. The proposed control scheme provides an accurate power supply while achieving 2-10 % higher power efficiency than conventional fixed on-time schemes with little circuit complexity added, which is critical during light-loading conditions, where quiescent current plays a pivotal role in determining efficiency and battery-life performance. Index Terms — Power supply IC, dc-dc converter, PFM control, adaptive on time T I.

Abstract — High-performance, state-of-the-art applications demand smart power supplies to be adaptive, power efficient, and reliably accurate, which is why monitoring inductor current flow in a lossless fashion is not only desirable but also critical for protection and feedback control. Filter-based lossless currentsensing technique use a tuned filter across the inductor to estimate current flow, and its accuracy is dependent on the inductance and equivalent series resistance (ESR) of the device. Because of process-related tolerances, errors as high as ±28% are reported, even when the nominal inductor value is known, which is not the case for the IC designer, whose errors will then grossly exceed this value. A technique is proposed to boost the accuracy of these current-sensing filters by automatically adjusting their bandwidth and gain via phase and gain feedback control loops. The proposed scheme essentially measures the inductance and ESR values during startup and power-on reset events. Because the filter is automatically tuned to the inductor, the current during normal operation can be measured accurately by simply sensing the voltage across the inductor. A PCB prototype implementation of the proposed technique achieved overall dc and ac gain errors of 2.3 % and 5 % at full load, respectively, when lossless, state-of-the-art schemes achieve 20-40 % error. Index Terns — power management, switching regulators, dcdc converters, current sensing, lossless, gm-C filter. I.

Abstract- This paper describes a digital pulse-width modulation/pulse-frequency modulation (PWM/PFM) controller with input voltage feed-forward for synchronous buck DC-DC converters. The controller includes automatic PWM/PFM mode switching and effective synchronous operation with a minimum number of active components and without the need for current sensing in PFM mode of operation. Input-voltage feed-forward improves efficiency and dynamic performance over a wide range of input voltages. Controller parameters, including the PWM switching frequency, the PFM pulse period, and the mode transition point are programmable, which enables efficiency optimization. Experimental results are shown for a synchronous buck converter with 5-to-12 V input voltage, and 1.3 V, 0 − 10 A output. I.

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