Chun Cheung

Power Loss Analyses for Dynamic Phase Number Control in Multiphase Voltage Regulators

To improve efficiency over a wide load range, it is important to dynamically adjust the operational phase number in multiphase voltage regulators. This paper analyzes in detail the power loss profile of a synchronous multi-phase buck converter and defines the optimal phase number under different load conditions. Experimental results are provided to verify the theoretical results.

Phase Doubler for high power voltage regulators

As the power consumption of microprocessors increases, a high phase count voltage regulator is required to meet the power hunger (>180A) and high efficiency requirements. In general, the higher the phase number count, the more PWM outputs and current sensing inputs are required for the PWM controller. Developing a very high phase count PWM controller becomes very challenging and requires a high pin count package, resulting in high cost and complex layout design. In this paper, a Phase Doubler, using a single PWM input to drive two interleaved phases, is proposed to overcome these problems. The Phase Doubler can be further expanded to quadruple the phase count, i.e, control 4 phases with only a single PWM input. Some experimental data of a 12-phase voltage regulator are included to verify the concept.

Desgin considerations of auto phase number control in multiphase voltage regulators

Automatic phase number control in multiphase voltage regulators can optimize the efficiency over a wide load range by adjusting the operational phase number according to the load current level. Several challenges limit its adoption in real applications. The dropped phases must respond immediately when a step load applies. The compensation network should be adjusted according to the phase number to keep the system stable under all operational conditions. The output voltage ripple and load line, during different phase number operation and during the transitioning of phase adding or dropping, should be kept within the spec. In this paper, some design considerations of auto phase number control are discussed in detail and illustrated with realizations of both optimal efficiency and transient performance across the entire load range.

Adaptive zero-current switching control scheme for diode emulation operation

A voltage regulator typically can achieve higher efficiency at very light load by operating in diode emulation mode rather than in continuous conduction mode. A very common approach to detect zero current crossing is to compare the phase-node voltage with zero volts or a few millivolts (mV) reference voltage. However the parasitic inductance may introduce some extra offset, resulting in early turn-off of the LGATE and extra power losses. The impact of power-train parasitics and operating conditions in diode emulation operation are studied in detail in this paper. A novel technique to compensate these variables and achieve zero-current switching (ZCS) diode emulation operation is presented. Experimental results are provided to verify the concept.

Small signal modeling of the hysteretic modulator with a current ripple synthesizer

In this paper, the synthetic ripple modulator for synchronous buck converter is modeled by the describing function approach. A detailed circuit configuration of the PWM modulator is introduced, including the hysteretic band control and the ripple synthesizer. The transfer function of the modulator is derived. By comparing the Bode plots for the open-loop hysteretic modulator and the closed-loop system, a good match is obtained between the analytical model and the SIMPLIS simulation results. The proposed model can be used in the design of the current ripple synthesizer to achieve fast transient response, and in the prediction of the system stability.

A new large signal average model for variable frequency pulse-width modulators

This paper introduces a large signal average model of a voltage regulator controlled by a variable frequency pulse width modulator (PWM). Variable frequency PWM techniques significantly reduce switching action delays and improve transient response compared to fixed frequency PWMs. The conventional average model cannot accurately predict the modulator behavior during variable frequency operation. In this paper, the effect on the modulator gain of the variable frequency operation is analyzed and incorporated in the average model. Using a variable frequency multiphase buck regulator in CPU core power applications as an example, the new large signal model is derived and demonstrated.

Small signal modeling of dual-edge PWM modulator with fixed clock frequency

In this paper, the describing function approach is used to model a dual-edge PWM modulator with a fixed clock frequency. A detailed PWM modulator circuit configuration is introduced with the derivation of the model. Good matching is observed when comparing the analytical model and SIMPLIS simulation. System level analysis demonstrates the advantages of the proposed model versus a conventional average model. The proposed model enables a more accurate compensator design for predicting the dynamic characteristics of the entire system.

Modeling a hysteretic modulator's PFM and PWM modes

In this paper, the describing function approach is used to extend the modeling of hysteretic mode control from the PWM mode to the PWM/PFM dual mode. A detailed circuit configuration of the PFM modulator and derivation of the model are introduced. Based on the derived model, a single zero transfer function is presented and several engineering approximations are applied to represent the dynamic characteristics of the PWM/PFM hysteretic modulator. A closed loop analysis is performed to assist the system designer with understanding the modulator.

Effects of edge termination using dielectric field plates with different dielectric constants, thicknesses and bevel angles

This paper investigates the effects of dielectric constants, thicknesses and bevel angles on the breakdown voltage (VBD) improvement of 4H - SiC Schottky Barrier Diodes (SBDs) using field plates (FP) edge termination. Three high-k dielectrics (AlN, AlON and HfO2) are studied separately as FP materials. Besides the variation in dielectric constants, distinctive thicknesses and bevel angles are applied to probe their effects in enhancing VBD of various device configurations. Simulation results obtained from TCAD Sentaurus device simulator have demonstrated that with proper design of materials, thicknesses and bevel angles, field crowding issue in planar devices can be well addressed and higher breakdown voltage can be acquired.

Comparison of linear and non-linear digital power solutions

Recently, digital power has gained some traction in computing applications. Digital powers allure is its flexibility and user interface. This paper compares the key performances of digital power solutions that use traditional non-linear (discrete) digital control and advanced linear digital control. Through detailed comparison, the proposed linear digital power solution that is realized with Intersils proprietary EAPP Digital and Auto Phase Number (APN) Control demonstrates the superior performance in transient response and high frequency current balance as well as overall efficiency without scarifying the flexible programmability and easy user interface.