An all GaN (Gallium Nitride) HEMTs (High Electron Mobility Transistors) based 48V to 12V Voltage Regulator Common Module (VRCM) is proposed in this paper for datacenter 48V rack. Furthermore, to achieve higher power density, a single core integrated planner transformer is also proposed. Lastly, a prototype of 1MHz 1kW module is demonstrated, achieving peak efficiency of 98.27% with 54V Vin and power density above 1000W/inch 3 .

LLC resonant converter is widely used in industry. However, up to now, no simple and accurate small-signal equivalent circuit model is available. This paper proposes an equivalent circuit model of LLC resonant converter. The simple equivalent circuit model is derived based on modification and simplification of extended describing function method. The model can well predicts the small-signal behaviors observed in LLC resonant converter, whenever switching frequency is below, close to or above the resonant frequency. For the first time, analytical expressions for control to output voltage, input to output voltage, input impedance and output impedance are provided to aid close loop feedback design. Simplis simulation and experimental results are presented to prove the accuracy of the model.

Inductors with ultra-low DC resistance (DCR) are preferred in DC-DC converters due to low power loss and high efficiency. Previous lossless DCR current sensing method suffers from bad current readback accuracy for ulta-low DCR inductors, due to leakage pin current of the controller. This paper proposes a novel accurate current sensing scheme to improve the current readback accuracy. Only one resistor and one capacitor are added into previous DCR current sensing scheme to balance the leakage pin current and improve noise immunity performance. The proposed scheme is low cost, and very simple for implementation. The experimental results verify the effectiveness of the proposed current sensing scheme. With the proposed current sensing scheme, +-3% current readback accuracy can be achieved in industry power uModule products [1] [2].

To achieve high power efficiency for step-up and step-down conversions, switching DC-DC power converters are widely used. However, the high di/dt and dv/dt transitions from switching converter operation create unwanted EMI noise which injects into the input and ground bus and interferes with other systems. To mitigate this, this paper presents an isolated gate driver and double-NMOS based switching DC-DC converter the Kappa converter which has both continuous input and output currents. With two inductors isolating both input and ground respectively as well as a minimized di/dt hot loop formed by a flying capacitor and two power switches, the Kappa buck and Kappa boost converters can be configured to achieve respective step-down and step-up voltage conversions. The Kappa buck converter, with one inductor connecting to input, has a continuous input current which can significantly reduce the input ripple, mitigate EMI noise and eliminate the need of bulky input EMI filters required by the conventional buck converter. Meanwhile, the entire load current is distributed between the two inductors to reduce DCR loss, but only two power switches are required compared to conventional two-phase buck converter. A Kappa buck converter with isolated gate driver is implemented to achieve a DC-DC conversion from 48V to 5V at an I-O up to 5A. Compared to a conventional buck converter with same passive component values and operating conditions, this Kappa converter has an input ripple of 14mV, achieving 86.7% input ripple suppression and 16dB peak EMI noise reduction.

Constant on-time V 2 control for point-of-load buck converters has instability issues in the cases that the output capacitors' RC time constants are small. This paper intensively studies the proposed solution using capacitor current ramp compensation, which is a superior solution featuring fast response and universality. A frequency-domain small-signal model based on describing function method is proposed in this paper. The time-domain large-signal response to the load step change is analyzed. The analysis illustrates the unique transient response behaviors of the capacitor current ramp compensated V 2 control. The design optimization methodology based on frequency-domain and time-domain analysis is presented. The proposed model and the design guidelines are verified by the experimental results.

One benefit of switching a converter at very high frequencies-even to the multimegahertz range-is that the loop bandwidth can be increased so that the transient performance is significantly improved. However, using the conventional small-signal model of continuous conduction mode (CCM) for quasi-square-wave (QSW) converters introduces a huge mismatch for the placement of the dominant poles when compared to the experiment results. The double poles in high-frequency QSW converters are split widely which cannot be predicted by the conventional model. A modified small-signal model of the QSW flyback converter is proposed to predict the double-pole splitting phenomenon and to analytically quantify the damping effect. The impacts of deadtime on control-to-output transfer function have been investigated in detail. The conventional CCM model turns out to be a special case of the proposed model. The theoretical analyses were eventually verified by Simplis simulation and experimental results on a 5-MHz QSW flyback converter.

Multiphase constant on-time current-mode control based on pulse distribution structure is widely used in voltage regulator application for microprocessor. To minimize ripple cancellation effect, external ramp compensation is used in commercial products. However, external ramp will introduce dynamic to the system and stability margin will be suffered without considering its effect. This paper first studies the effect of external ramp by deriving small-signal transfer function based on describing function method. It is found that external ramp brings additional dynamic, with time constant related with switching period. Then, a simple equivalent circuit model based on three-terminal switch concept is proposed, which considers the effect of external ramp by adding an additional R-L branch. The equivalent circuit model can be reduced to previous unified three-terminal switch model when external ramp is zero and can be reduced to model of constant on-time voltage mode control when external ramp is much larger than inductor current ramp. The proposed three-terminal switch model is a complete model, which can be used to examine all transfer functions and is accurate up to half of switching frequency. The analytical transfer functions are provided for easy reference. The model is verified by SIMPLIS simulation and experimental measurement.

V 2 control has advantages of simple implementation and fast transient response and is widely used in industry for point-of-load applications. This control scheme is elegant when output capacitors with large RC time constant are employed, such as OSCON capacitors. However, in most cases using capacitors with small RC time constant, such as ceramic capacitors, instability problem will occur. Previous modeling methods including sampled-data modeling, discrete-time analysis, time-domain analysis, and describing function are all very mathematical and difficult to apply for practical engineers as little physical insight can be extracted. Up to now, no equivalent circuit model is proposed which is able to predict the instability issue and serve as a useful design tool for V 2 control. This paper proposes a unified equivalent circuit model which is applicable to all types of capacitors by considering the effect of capacitor voltage ripple. The equivalent circuit provides the physical insight of V 2 control as a nonideal voltage source, a dual concept of previous nonideal current source for current-mode control. The equivalent circuit model is a simple yet accurate complete model and is very helpful for design purpose. Optimal design guidelines for point-of-load applications are provided. The proposed equivalent circuit model is applicable to both variable frequency modulation and constant frequency modulation. The equivalent circuit model and design guidelines are verified with Simplis simulation and experimental results.

Recently, V2 control and its variety named ripple-based control has been gaining more and more popularity in academia research and commercial products. However, for constant frequency V2 control, design methodology is not clear due to insufficient knowledge about the small-signal model. This paper investigates the small-signal model and optimal design strategy for constant frequency V2 control. The factorized small-signal control-to-output voltage transfer function and output impedance are investigated. The stability criterion is obtained and design considerations are analyzed. Moreover, the small-signal model with ramp compensations is presented and optimal design guidelines from dynamic performance point of view are provided. For the first time, it is found the external ramp is good enough to get a well-damped performance when current feedback strength is strong (for example, when employing OSCON capacitors). However, the current ramp is necessary to achieve a good dynamic performance when the current feedback strength is weak (for example, when employing ceramic capacitors). As a result, a new control strategy with the hybrid ramp is proposed for ceramic capacitor applications. The small-signal model and proposed design guidelines are verified with Simplis simulation and experimental results.

Recently, V2 control and its variety named ripple-based control has been gaining more and more popularity in academia research and commercial products. However, for constant frequency V2 control, design methodology is not clear due to insufficient knowledge about the small-signal model. This paper investigates the small-signal model and optimal design strategy for constant frequency V2 control. The factorized small-signal control-to-output voltage transfer function and output impedance are investigated. The stability criterion is obtained and design considerations are analyzed. Moreover, the small-signal model with ramp compensations is presented and optimal design guidelines from dynamic performance point of view are provided. For the first time, it is found the external ramp is good enough to get a well-damped performance when current feedback strength is strong (for example, when employing OSCON capacitors). However, the current ramp is necessary to achieve a good dynamic performance when the current feedback strength is weak (for example, when employing ceramic capacitors). As a result, a new control strategy with the hybrid ramp is proposed for ceramic capacitor applications. The small-signal model and proposed design guidelines are verified with Simplis simulation and experimental results.

Recently, V 2 control and its variety named ripple-based control has been gaining more and more popularity in academia research and commercial products. However, for constant frequency V 2 control, design methodology is not clear due to insufficient knowledge about the small-signal model. This paper investigates the small-signal model and optimal design strategy for constant frequency V 2 control. The factorized small-signal control-to-output voltage transfer function and output impedance are investigated. The stability criterion is obtained and design considerations are analyzed. Moreover, the small-signal model with ramp compensations is presented and optimal design guidelines from dynamic performance point of view are provided. For the first time, it is found the external ramp is good enough to get a well-damped performance when current feedback strength is strong (for example, when employing OSCON capacitors). However, the current ramp is necessary to achieve a good dynamic performance when the current feedback strength is weak (for example, when employing ceramic capacitors). As a result, a new control strategy with the hybrid ramp is proposed for ceramic capacitor applications. The small-signal model and proposed design guidelines are verified with Simplis simulation and experimental results.

A simple third-order equivalent circuit model of series resonant converter (SRC) is proposed in this paper. Up to now, the most successful equivalent circuit model of SRC is based on extended describing function concept, which is proposed by Dr. E. Yang [30]. However, the equivalent circuit is a complicated fifth-order circuit with the cross-coupling effect and no analytical solution is provided for transfer functions. This paper proposes a methodology to simplify the fifth-order equivalent circuit to a third-order equivalent circuit. The equivalent circuit model can predict the dynamic behavior very well when switching frequency is below, close to or above resonant frequency. Furthermore, for the first time, analytical expressions of transfer functions are provided to serve as a useful tool for feedback design. The equivalent circuit model is verified by Simplis simulation and experimental results.

Multi-phase constant on-time current mode control based on pulse distribution structure is widely used in Voltage Regulator application for microprocessor. To minimize ripple cancellation effect, external ramp compensation is used in commercial products. However, external ramp will introduce dynamic to the system and AVP requirement will be violated without considering its effect. This paper first studies the effect of external ramp by deriving small-signal transfer function based on describing function method. It is found that external ramp brings additional dynamic, with time constant related with switching period. Then, a simple equivalent circuit model based on three-terminal switch concept is proposed, which considers the effect of external ramp by adding an additional R-L branch. The equivalent circuit model can be reduced to previous unified three-terminal switch model when external ramp is zero and can be reduced to model of constant on-time voltage mode control when external ramp is much larger than inductor current ramp. The proposed three-terminal switch model is a complete model which can be used to examine all transfer functions and is accurate up to half of switching frequency. The model is verified by Simplis simulation.

Recently, constant on-time V2 control, and its variety named constant on-time control, or constant on-time ripple-based control is more and more popular in industry products due to features of high light-load efficiency, simple implementation, and fast transient response. However, subharmonic oscillation occurs when using multilayer ceramic caps due to the lagging phase of the capacitor voltage relative to the inductor current. External ramp compensation is one simple solution to solve the instability issue. However, the characteristics of constant on-time V2 control with external ramp are not fully understood and no explicit design guidelines for the external ramp are provided. This paper investigates the small-signal characteristics of constant on-time V2 control with external ramp compensation by providing a factorized, easy-to-use small-signal model. The external ramp is a critical parameter because it directly affects the position and damping of two pairs of double poles. Based on this fact, design guidelines of the external ramp for optimal dynamic performance are provided. Moreover, the effect of duty cycle is investigated. Finally, the small-signal experimental results and load transient performance are presented to verify the small-signal analysis and proposed design guideline.

V2 control and its variety named ripple-based control, are popular control schemes in point-of-load Buck converters and Voltage Regulators for microprocessor. This control scheme is elegant when output capacitors with sufficient ESR are employed, such as OSCON capacitors. However, in most cases with small-ESR capacitors, such as ceramic capacitors, instability problem will occur. Up to now, no equivalent circuit model is proposed which is able to predict instability issue. This paper proposes a unified equivalent circuit model which is suitable to all kinds of capacitors by considering the effect of both inductor current ripple and capacitor voltage ripple. The equivalent circuit model is a simple yet accurate, complete model and can be used to investigate all transfer functions. The proposed equivalent circuit model is applicable to both variable frequency modulation and constant frequency modulation. Furthermore, the model can be extended to enhanced V2 control and muti-phase V2 converters. The equivalent circuit model is verified with Simplis simulation and experimental results.

This paper presents a digital hybrid ripple-based constant on-time control scheme for voltage regulator modules (VRMs). Due to the sampling effects of the digital implementation, the stability issue becomes worse than the analog ripple-based control schemes, especially when low-ESR decoupling capacitors are used as the output filter. In order to stabilize the system and to fulfill the output impedance requirement of adaptive voltage positioning (AVP), a hybrid ramp compensation strategy, which includes the external ramp and the estimated current ramp, is proposed. The small-signal model of the proposed architecture is derived to provide the design guideline for the ramp compensation gains and the number of output and decoupling capacitors. Besides, only low sampling-rate Analog-to-Digital Converters (ADCs) are required to sample the input voltage, the output voltage, and the average current making the proposed architecture compatible with the cost/complexity constraints of VRM applications. Simulation and experimental results show that the ripple-based control can achieve high-bandwidth performance, and the proposed digital control architecture can fulfill the AVP design requirements of single-phase VRMs.

Recently, constant on-time V2 control, and its variety named constant on-time control, or constant on-time ripple-based control is more and more popular in industry products due to features of high light-load efficiency, simple implementation, and fast transient response. However, subharmonic oscillation occurs when using multilayer ceramic caps due to the lagging phase of the capacitor voltage relative to the inductor current. External ramp compensation is one simple solution to solve the instability issue. However, the characteristics of constant on-time V2 control with external ramp are not fully understood and no explicit design guidelines for the external ramp are provided. This paper investigates the small-signal characteristics of constant on-time V2 control with external ramp compensation by providing a factorized, easy-to-use small-signal model. The external ramp is a critical parameter because it directly affects the position and damping of two pairs of double poles. Based on this fact, design guidelines of the external ramp for optimal dynamic performance are provided. Moreover, the effect of duty cycle is investigated. Finally, the small-signal experimental results and load transient performance are presented to verify the small-signal analysis and proposed design guideline.

In V-2 control, the direct feedback contains the information of the inductor current, the capacitor voltage, and the load current. In this paper, by separating the current feedbacks and the capacitor voltage feedback, an equivalent circuit of V-2 control with ESR dominant output capacitor is proposed. The proposed equivalent circuit is based on the unified equivalent circuit of current mode controls. It is a completed frequency domain model for V-2 control with a clear physical insight. V-2 control can be interpreted as an advanced implementation of current mode control with a proportional voltage feedback and an additional load current feedback. The load current feedback dramatically reduces the output impedance of a current mode controlled converter. The model is extended to the enhanced V-2 control. The proposed-model is applicable to both variable frequency modulations and constant frequency modulations. The modeling results are verified by the Simplis simulation and the experimental results.