Julu Sun

High Power Density, High Efficiency System Two-stage Power Architecture for Laptop Computers

This paper proposes system two-stage power architecture for laptop voltage regulators (VRs). By taking advantage of the Thermal Design Power (TDP) requirement in the laptop, VRs for microprocessor, graphics, DDR memory and main power can share the same first stage with very low design power. The high-efficiency and high-frequency first stage based on switching capacitor technology and second stage design is presented in this paper respectively. Two different designs are illustrated and verified by experiments. One design keeps the similar VR cost as the current single-stage solution and improves VR light load efficiency by 5%. Another design has slightly higher VR efficiency comparing with single-stage solution while reducing the footprint of VR output inductors and capacitors by 25%∼33% and VR total cost by 5%.

Adaptive voltage position design for voltage regulators

This paper proposes a general design guideline for the voltage regulator (VR) to achieve adaptive voltage position (AVP). All existing control methods are covered for different kinds of output filter capacitors. Based on the small-signal model analysis, the output impedance and system control bandwidth are discussed. Following the proposed design guidelines, simulation and experimental results demonstrate very good VR transient response.

A family of high power density unregulated bus converters

This paper begins by reviewing current bus converters and exploring their limitations. Next, a family of inductor-less bus converters is proposed to overcome the limitations. In the new bus converters, magnetizing current is used to achieve zero-voltage-switching (ZVS) turn-on for all switches. The resonant concept is used to achieve nearly zero-current-switching (ZCS) turn-off for the primary switches and no body diode loss for the synchronous rectifiers (SRs). Meanwhile, the self-driven method can be easily applied to save drive loss of SRs. Based on these concepts, a full-bridge bus converter is built in the quarter-brick size to verify the analysis. The experimental results indicate that it can achieve 95.5% efficiency at 500-W, 12-V/45-A output. Compared with industry products, this topology can dramatically increase the power density. These concepts are also applied to nonisolated dc/dc converters. As an example, a resonant Buck converter is proposed and experimentally demonstrated.

A self-driven soft-switching voltage regulator for future microprocessors

In conventional high frequency 12-V input voltage regulators (VR), large gate driver loss and body diode conduction loss raise crucial challenges to its gate driver implementation. The proposed self-driven topologies are basically buck-derived multiphase interleaving soft switching topologies, which eliminate the synchronous rectifier MOSFET drivers and save driving loss and body diode loss, so that it is a high efficiency, high power density solution for future microprocessors. A 1U four-phase 1.3-V/100-A VRM running at 1MHz demonstrates its advantages (cost, size and efficiency) over the conventional multiphase buck converter.

Light-Load Efficiency Improvement for Buck Voltage Regulators

Extending battery life is a big challenge for todays laptop, and light-load efficiency is very important for battery life extension. In this paper, adaptive ON-time control is proposed to achieve higher efficiency when the buck converter is running in continuous current mode. A novel nonlinear inductor is then proposed to improve discontinuous-current-mode efficiency. A control method with a thorough analysis is proposed for the nonlinear inductor to achieve high efficiency, the required output voltage ripple, and sufficient transient response. The experimental results demonstrate the benefits of the proposed methods.

Technology road map for high frequency integrated DC-DC converter

This preliminary road map is provided for state-of-the-art technologies and trends toward integration of point-of-load converters. This paper encompasses an extended survey of literature ranging from device technologies and magnetic materials to integration technologies and approaches. The paper is organized into three main sections. 1) Device technologies, including the trench MOSFET, lateral MOSFET and lateral trench MOSFET, are discussed along with their intended applications. The critical role of device packaging to high-frequency integration is assessed. 2) Magnetic materials: In recent years, a number of new magnetic materials have been explored in various research labs to facilitate magnetic integration for high-frequency POL applications. These data are collected and organized to help selecting magnetic material for various current levels and frequency ranges. 3) Levels of integration, which are defined with the focus on magnetic integration techniques and approaches, namely board-level, package-level and wafer-level, each with suitable current scale and frequency range.

A Novel Input-Side Current Sensing Method to Achieve AVP for Future VRs

This paper proposes a new input-side current sensing method for the voltage regulator (VR) to achieve adaptive voltage position (AVP). By applying the proposed method, both good current sensing accuracy and low power dissipation can be achieved. The transient and tolerance analysis of this method are provided and a design guideline is illustrated and experimentally verified

Technology roadmap for high frequency integrated DC-DC converter

This preliminary roadmap is provided for state-of-the-art technologies and trends toward integration of point-of-load converters. This paper encompasses an extended survey of literature ranging from device technologies and magnetic materials to integration technologies and approaches. The paper is organized into three main sections. 1) Device technologies, including the trench NIOSFET, lateral MOSFET and lateral trench MOSFET, are discussed along with their intended applications. The critical role of device packaging to highfrequency integration is assessed. 2) Magnetic materials: In recent years, a number of new magnetic materials have been explored in various research labs to facilitate magnetic integration for high-frequency POL applications. These data are collected and organized to help selecting magnetic material for various current levels and frequency ranges. 3) Levels of integration, which are defined with the focus on magnetic integration techniques and approaches, namely board-level, package-level and wafer-level, each with suitable current scale and frequency range.

High Power Density Voltage Divider and Its Application in Two-Stage Server VR

This paper starts with the two-stage Voltage-Regulator (VR) solution for future server microprocessors. By using two-stage solution, high efficiency and high power density VR can be put as close as the microprocessor to eliminate the interconnection effect. Then, high efficiency high power density voltage divider which is served as the 1st stage is analyzed and optimal design is illustrated. Finally, a 2500 W/in3 interleaved voltage divider with 97~98% efficiency is experimentally verified.

High efficiency quasi-parallel Voltage Regulators

High efficiency voltage regulators (VR) are desired for battery life extension and energy saving. In this paper, a novel quasi-parallel VR architecture is proposed. Its working principle and small signal model are illustrated in detail. The proposed VR takes advantage of the high-efficiency, fast-transient unregulated converter and relies on it to deliver most of the output power, while uses low power Buck type converter to achieve voltage regulation. The simulation and preliminary experimental results demonstrate that the proposed VR can achieve 4%-5% higher efficiency than state-of-the-art multi-phase buck VR and it can eliminate all the output bulk capacitors with 600k Hz switching frequency.