Shamala A. Chickamenahalli

Effect of target impedance and control loop design on VRM stability

Stability analysis of a VRM used in a typical microprocessor power supply application is presented. With every generation of microprocessors, the decreasing voltages, increasing currents and di/dts are demanding faster VRM transient responses. This analysis focuses on the influence of constantly dropping target impedances and increasing crossover frequencies on the output of multi-phase, high-frequency synchronous rectifier type DC-DC converters. Attempts are made to relate the switching frequency of the VRM to its stability regime. Results are summarized with guidelines on feedback loop stabilization under diminishing target impedances.

VR Transient Improvement at High Slew Rate Load—Active Transient Voltage Compensator

To meet the stringent transient response requirements of a voltage regulator (VR) at high slew rate load current while keeping high VR efficiency, this paper proposes a new topology: active transient voltage compensator (ATVC). ATVC only engages in transient periods operating at several MHZ to handle ac current and main VR operates at low switching frequency for better efficiency mainly providing dc current. ATVC injects a very high slew rate current in step up load and recovers energy in step down load. With introduction of a transformer, ATVC significantly reduces its conduction and switching losses due to the reduced current. Also, the new topology reduces the number of VR bulk capacitors while keeping the same output impedance. A built prototype and detailed experimental results verify the theoretical analysis.

RF packaging and passives: design, fabrication, measurement, and validation of package embedded inductors

Design, modeling, and characterization of inductors embedded in a package substrate promising higher quality factor (Q) and lower cost than on-chip inductors is described. In addition to the problem of large conductor losses, on-die inductors with or without magnetic materials consume considerable die area and require the removal of the first-level interconnect bumps beneath them to maintain a reasonably high Q value. Moving inductors to the package eliminates the need for bump array depopulation and, thus, mitigates the potential reliability problems caused by voids in the epoxy underfill between the die and the substrate. Competency developed to design, fabricate, and characterize inductors based on standard organic flip-chip packaging technology is described. Physical design details along with measurement procedures and results are discussed. In addition, modeling techniques for achieving good correlation to measured data are included.

Microprocessor platform impedance characterization using VTT tools

This paper presents a method to extract the impedance profile of Intel processor platforms in frequency domain using custom, high di/dt electronic loads referred as VTT tools. Although currently followed time domain characterization yields the voltage response of the motherboard (MBD) to the current profile generated by the VTT tool, it does not directly provide the MBD impedance as a function of frequency. Without knowledge of the impedance profile it is difficult to fully understand the impact motherboard layout and decoupling capacitor filter configurations have on the overall power delivery system performance. Theory of the method, VTT tool modifications and platform waveform results discussed. Internally developed computer scripts that process the ratio of the measured voltage and current FFTs as the platform impedance over frequency are described. Correlation of simulation models is provided. Steps towards generalization of the method for maximum industry adoption are identified

Fast Load Transient Regulation of Low-Voltage Converters with the Low-Voltage Transient Processor

The transient response of DC-DC converters with large conversion ratios is limited by the asymmetry of the current slew rate through the magnetic elements; under appropriate control, such a converter may respond much faster to an increase in load current than a decrease, or vice versa. In this paper, a low-voltage, unloaded, bidirectional DC-DC converter with a very fast current slew rate, called the low-voltage transient processor (LVTP), is placed in shunt across the output of a conventional DC-DC converter (the ldquoprimary regulatorrdquo) to equalize the effective current slew rate (the combination of the LVTP and primary regulator) seen at the load, so that the transient response to a load increase is the same as the response to a load decrease. The LVTP operates at very low voltages, enabling the use of small magnetic components with low losses even at high-frequency operation, allowing the overall efficiency of the system to be high. To demonstrate the concept, a 3 MHz bidirectional buck LVTP prototype was implemented and placed at the output of a 12-1.2 V microprocessor voltage regulator (VR). The VR with LVTP matched the performance of VRD10.1 VR reference design with half (4.10 mF) of the output capacitance of the original design.

Active transient voltage compensator design for VR load line improvement

Active transient voltage compensator (ATVC), only engaged in transient periods, was proposed to improve the VR load line and main VR can be optimized design with better efficiency which mainly handles the dc current. ATVC has reduced switching and conduction losses in extra converter due to the introduction of a transformer and it can also reduce the number of VR capacitors for required voltage tolerance. The compensation network delay times deteriorate the second voltage spike at high slew rate transient, especially in the high bandwidth controller. In this paper, combination of linear and adaptive nonlinear control is used to reduce the delay times of the compensation network. Finally a prototype of 3-Ch VR + ATVC was carried out on Intel motherboard and detailed experimental results are given.

A DSP controlled variable-frequency resonant-commutated converter

Features of a three-phase resonant-commutated variable-frequency converter applicable in a variety of industrial applications are presented. Minimization of switching losses and hence usage of naturally commutated devices as accomplished by resonant commutation of the converter is highlighted. Design and development of the TMS320C30 DSP based controller is described. Strategies developed for switching of converter devices in relation to the resonant-commutated link are discussed. Results from Pspice simulation studies of the converter are presented. Experimental results while the three-phase experimental model of the converter supplied passive loads are enclosed and observations summarized. Comparison of results confirms potential applicability of the converter in adjustable speed drive, induction heating, welding and active filter applications.