Transient Response Improvement For Multi-phase Voltage Regulators

Next generation microprocessor (Vcore) requirements for high current slew rates and fast transient response together with low output voltage have posed great challenges on voltage regulator (VR) design . Since the debut of Intel 80X86 series, CPUs have greatly improved in performance with a dramatic increase on power consumption. According to the latest Intel VR11 design guidelines , the operational current may ramp up to 140A with typical voltages in the 1.1V to 1.4V range, while the slew rate of the transient current can be as high as 1.9A/ns [1, 2]. Meanwhile, the transient-response requirements are becoming stringer and stringer. This dissertation presents several topics on how to improve transient response for multi-phase voltage regulators. The Adaptive Modulation Control (AMC) is a type of non-linear control method which has proven to be effective in achieving high bandwidth designs as well as stabilizing the control loop during large load transients. It adaptively adjusts control bandwidth by changing the modulation gain, depending on different load conditions. With the AMC, a multiphase voltage regulator can be designed with an aggressively high bandwidth. When in heavy load transients where the loop could be potentially unstable, the bandwidth is lowered. Therefore, the AMC provides an optimal means for robust high-bandwidth design with excellent transient performance. The Error Amplifier Voltage Positioning (EAVP) is proposed to improve transient response by removing undesired spikes and dips after initial transient response. The EAVP works only in a short period of time during transient events without modifying the power stage and changing the control loop gain. It facilitates the error amplifier voltage recovering during transient events, achieving a fast settling time without impact on the whole control loop. Coupled inductors are an emerging topology for computing power supplies as VRs with coupled inductors show dynamic and steady-state advantages over traditional VRs. This dissertation first covers the coupling mechanism in terms of both electrical and reluctance modeling. Since the magnetizing inductance plays an important role in the coupled-inductor operation, a unified State-Space Averaging model is then built for a two-phase coupled-inductor voltage regulator. The DC solutions of the phase currents are derived in order to show the impact of the magnetizing inductance on phase current balancing. A small signal model is obtained based on the state-space-averaging model. The effects of magnetizing inductance on dynamic performance are presented. The limitations of conventional DCR current-sensing for coupled inductors are addressed. Traditional inductor DCR current sensing topology and prior arts fail to extract phase currents for coupled inductors. Two new DCR current sensing topologies for coupled inductors are presented in this dissertation. By implementation of simple RC networks, the proposed topologies can preserve the coupling effect between phases. As a result, accurate phase inductor currents and total current can be sensed, resulting in excellent current and voltage regulation. While coupled-inductor topologies are showing advantages in transient response and are becoming industry practices, they are suffering from low steady-state operating efficiency. Motivated by the challenging transient and efficiency requirements, this dissertation proposes a Full Bridge Coupled Inductor (FBCI) scheme which is able to improve transient response as well as savor high efficiency at (a) steady state. The FBCI can change the circuit configuration under different operational conditions. Its flexible topology is able to optimize both transient response and steady-state efficiency. The flexible core configuration makes implementation easy and clear of IP issues. A novel design methodology for planar magnetics based on numerical analysis of electromagnetic fields is offered and successfully applied to the design of low-voltage high power density dc-dc converters. The design methodology features intense use of FEM simulation. The design issues of planar magnetics, including loss mechanism in copper and core, winding design on PCB, core selections, winding arrangements and so on are first reviewed. After that, FEM simulators are introduced to numerically compute the core loss and winding loss. Consequently, a software platform for magnetics design is established, and optimized magnetics can then be achieved. Dynamic voltage scaling (DVS) technology is a common industry practice in optimizing power consumption of microprocessors by dynamically altering the supply voltage under different operational modes, while maintaining the performance requirements. During DVS operation, it is desirable to position the output voltage to a new level commanded by the microprocessor (CPU) with minimum delay. However, voltage deviation and slow settling time usually exist due to large output capacitance and compensation delay in voltage regulators. Although optimal DVS can be achieved by modifying the output capacitance and compensation, this method is limited by constraints from stringent static and dynamic requirements. In this dissertation, the effects of output capacitance and compensation network on DVS operation are discussed in detail. An active compensator scheme is then proposed to ensure smooth transition of the output voltage without change of power stage and compensation during DVS. Simulation and experimental results are included to demonstrate the effectiveness of the proposed scheme

Planar Magnetics Design For Low-voltage Dc-dc Converters

The objectives of this thesis are to design planar magnetic devices based on accurate electromagnetic analysis and miniaturize magnetics within desired low profile as well as small footprint. A novel methodology based on FEM simulation is proposed. By introducing Maxwell 2D simulator, optimal interleaving structures can be found to reduce AC losses that cannot otherwise be accounted for by conventional method. And 3D simulator is employed to make the results more realistic. Thus, high-efficiency high-power density magnetics is achieved

A Novel Control For Two-Stage Dc/Dc Converter With Fast Dynamic Response

This paper investigates the dynamic response relationship with nonlinear gain instead of conventional linear relationship in two-stage DC-DC converter, and proposes a simple novel control method for two-stage converter with fast dynamic response; it has large operating duty ratio and large voltage step-down ratio, suitable for low voltage application. Most importantly, it can achieve fast dynamic response without pushing higher frequency due to its large voltage gain slew rate. Finally an experimental prototype was carried out to verify the theoretic analysis

Adaptive Nonlinear Compensation For Asymmetrical Half Bridge Dc-Dc Converters

Asymmetrical half-bridge dc-dc converter has favorable features, which allow the converter to operate at higher frequencies with higher power density. However, asymmetrical half bridge dc-dc converter displays nonlinear dc gain variation with input voltage and duty cycle. The conventional compensator design is based on a small-signal transfer function of power stage and worst case has to be considered in the closed-loop design. With the variation of input line, the system loop gain deviates from the nominal designed trajectory, and correspondingly, the system bandwidth, phase margin and gain margin are going to vary with input voltage line. As a result, the system steady-state and dynamic performance are affected as well. This paper proposes an adaptive nonlinear compensation approach to adjust the system loop gain dynamically and thus achieve unified system loop gain, bandwidth and performance. The adaptive digital compensation algorithm is simulated and verified based on PSIM simulation software. © 2006 IEEE

Power Losses Estimation Platform For Power Converters

A power losses analysis platform integrating powerful analysis software Pspice™, MathCAD™ and Maxwell™ capable of calculating losses on the key components in converters is presented. The operational block diagram and the analysis principle, as well as the technical issue, are discussed. One analysis example is given and the prototype is built. The validity of the analysis is verified by the experimental results

Investigating Effects Of Magnetizing Inductance On Coupled-Inductor Voltage Regulators

Coupled inductors are an emerging topology for computing power supplies as next generation CPU requirements for high efficiency and fast transient response pose great challenge on voltage regulator design. This paper addresses the effects of magnetizing inductance on current-balancing, dynamic response, and current-sensing of multiphase voltage regulator with coupled inductors. State Space Averaging and other mathematical analysis methods are employed. Experimental results are provided to verify the analysis. ©2008 IEEE

Parasitic Resistance Current Sensing Topology For Coupled Inductors

Traditional current sensing topology based on inductor equivalent series resistance fails to extract phase currents for coupled inductors due to the presence of the magnetising inductance. This article proposes a new direct-current resistance current sensing topology for coupled inductors. By implementation of a simple resistor-capacitor network, the proposed topology can preserve the coupling effect between phases. As a result, real phase inductor currents and total current can be sensed. Detailed mathematical analysis and design equations are presented in this article. Sensitivity and mismatch issues are addressed. Experimental results show that the proposed topologies are able to extract phase current as well as total current with acceptable accuracy

Improving Transient Performance For Voltage Regulators With Error Amplifier Voltage Positioning

Next generation microprocessor requirements for high current slew rates and fast transient response together with low output voltages have posed great challenges on voltage regulator (VR) design. This paper presents a new Error Amplifier Voltage Positioning (EAVP) method which has proven to be effective in achieving fast transient response for voltage regulators. Unlike prior arts of non-linear control methods, it does not modify the power stage nor change the control loop gain. Instead, it helps error amplifier recover from its saturation status during transient events. Operational mechanism of the EAVP is presented in this paper in detail. Simulation results and experimental data show that the EAVP scheme settles down the output voltage quickly after a heavy load transition, resulting in excellent transient performance without impact on other operations. © 2007 IEEE

An Active Compensator Scheme For Dynamic Voltage Scaling Of Voltage Regulators

Dynamic voltage scaling (DVS) technique is a common industry practice in optimizing power consumption of microprocessors by dynamically altering the supply voltage under different operational modes, while maintaining the performance requirements. During DVS operation, it is desirable to position the output voltage to a new level commanded by the microprocessor (CPU) with minimum delay. However, voltage deviation and slow settling time usually exist due to large output capacitance and compensation delay in voltage regulators. Although optimal DVS can be achieved by modifying the output capacitance and compensation, this method is limited by constraints from stringent static and dynamic requirements. In this paper, the effects of output capacitance and compensation network on DVS operation are discussed in detail. An active compensator scheme is then proposed to ensure smooth transition of the output voltage without change of power stage and compensation during DVS. Simulation and experimental results are included to demonstrate the effectiveness of the proposed scheme. © 2009 IEEE

Adaptive Modulation Control For Multiple-Phase Voltage Regulators

This paper presents a new Adaptive Modulation Control (AMC) method which has proven to be very effective in achieving high bandwidth designs. AMC is a type of nonlinear control since it works only during large dynamic load transitions. Influence of AMC in both the time domain and frequency domain is analyzed. Simulation results and experimental data are included to show a very high bandwidth as well as excellent transient performance. © 2007 IEEE