An Average Inductor Current Sensor with Enhanced Accuracy in DCM for Buck Converters

This paper presents comparison of a recently proposed tuned-average current-mode with widely accepted average current-mode, in order to control the average inductor current of the constant frequency DC/DC power converters. The buck converter was taken as an example to demonstrate superior features of the tuned-average current-mode. Some frequency-domain characteristics are investigated and the conclusions are verified through simulations. Finally, the design considerations for both methods were emphasized as a helping tool for the designer to choose the control method which will meet his needs.

A new two-dimensional random switching PWM technique is proposed to reduce the dominant harmonic clusters while retaining constant average inductor current and constant sampling frequency. The special feature of constant average inductor current can reduce the output voltage ripple. And the controller parameters of digital-controlled power converter are not required to change which is quite essential to digital-controlled system. Current random PWM methods are discussed and compared with the proposed method in this paper. It will be shown that the presented method is with the merits of randomly changes switching frequency while keeping constant sampling frequency and average inductor current. An FPGA-based digital-controlled buck converter experimental system has been set up. The specifications of the converter includes: input voltage = 5 V, output voltage = 1.5 V and switching frequency = 200 kHz. The proposed random switching pattern is implemented by software. Experimental results demonstrate the effectiveness of the proposed random switching pattern.

The method of extended linearization is used to design stabilizing nonlinear proportional-integral feedback controllers which regulate to a constant set-point value the average output inductor current, the average input inductor current, or the average transfer capacitor voltage of a PWM (pulse width modulation) controlled Cuk converter. The design is carried out on the basis of the frequency domain Ziegler-Nichols method applied to a family of linearized transfer function models of the converter, parametrized by constant operating equilibrium points of the average PWM controlled circuit. Some simulation examples highlighting the nonlinear P-I controller performance are presented. The nonlinear controller scheme, as applied to the actual discontinuous PWM regulated Cuk converter, is shown to comply with the same qualitative stabilization features that are imposed on the average model design, provided the output feedback signal is properly processed through a low pass filter with a small cut-off frequency and a sufficiently high sampling frequency is used in the PWM actuator.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The method of extended linearization is used for designing stabilizing nonlinear proportional-integral (PI) feedback controllers which regulate to a constant set-point value either the average output inductor current, the average input inductor current, or the average transfer capacitor voltage of a pulse width modulation (PWM) controlled Cuk converter. The design is carried out on the basis of the frequency-domain Ziegler-Nichols method, applied to a family of transfer function models of the linearized average PWM controlled circuit, parametrized by constant operating equilibrium points.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A step-up/step-down DC-DC converter with high efficiency and small output voltage ripple is proposed in this paper. To reduce the switching loss and improve the efficiency, the converter operates in buck or boost mode when the input voltage is much higher or lower than the output voltage. However, a large output voltage ripple appears at the boundary of buck mode and boost mode due to the speed limitation of standard analog circuit. A transition mode using a digital dither technique is adopted and the output voltage ripple is reduced when the input voltage is close to the output voltage. Furthermore, the average inductor current is also reduced in the proposed transition mode. The converter has been designed with a standard a 0.5 μm CMOS process. The peak efficiency is 96% and the output voltage ripple is reduced to less than 10 mV in the transition mode.

This paper presents a current mode step-up/step-down DC–DC converter with high efficiency, small output voltage ripple, and fast transient response. The control scheme adaptively configures the converter into the proper operation mode. The efficiency is improved by reducing the switching loss, wherein the converter operates like a buck or boost converter, and conduction loss, wherein the average inductor current is reduced in transition modes. The output voltage ripple is significantly reduced by incorporating two constant time transition modes. A fast line transient response is achieved with small overshoot and undershoot voltage. An adaptive substrate selector (ASS) is introduced to dynamically switch the substrate of PMOS power transistors to the highest on-chip voltage. A lossless self-biased current sensor with high-speed and high-accuracy is also achieved. The proposed converter was designed with a standard 0.5 μm CMOS process, and can regulate an output voltage within the input voltage ranged from 2.5 V to 5.5 V. The maximum load current is 600 mA, and the maximum efficiency is 94%. The output voltage ripple is less than 15 mV in all operation modes.

The Deep Space Avionics (DSA) Project is developing a Power Actuation and Switching Module (PASM). This component enables a modular and scalable design approach for power switching applications, which can result in a wide variety of power switching architectures using this simple building block. The PASM is designed to provide most of the necessary power switching functions of spacecraft for various Deep Space missions including future missions to Mars, comets, Jupiter and its moons. It is fabricated using an A SIC process that is tolerant of high radiation. The development includes two application specific integrated circuits (ASICs) and support circuitry all packaged using High Density Interconnect (HDI) technology. It can be operated in series or parallel with other PASMs, It can be used as a high-side or low-side switch and it can drive thruster valves, pyrotechnic devices such as NASA standard initiators, bus shunt resistors, and regular spacecraft component loads. Each PASM contains two independent switches with internal current limiting and over-current trip-off functions to protect the power subsystem from load faults. During turnon and turnoff each switch can limit the rate of current change (di/dt) to a value determined by the user. Threeway majority-voted On/Off commandability and full switch status telemetry (both analog and digital) are built into the module. This paper describes the development process used to design, model, fabricate, and test these compact and versatile power switches. Preliminary test results from prototype HDI PASM hardware are also discussed.

System fault mode considerations make high side switching desirable in many automotive applications. These switches must withstand 10 kV module level electro-static discharge and 60 V alternator load dump. An automotive high side switch (HSS) must control negative inductive flyback voltages during normal operation and during loss of battery. To control high current loads in the automotive environment, an HSS must also be able to operate with an ambient temperature up to 125/spl deg/C. Motorola is in production with two dual output high side switches for the automotive industry. These high side switches provide real-time diagnostics while controlling up to four ampere loads at 105/spl deg/C. This paper discusses the features available in this family of HSS ICs and their operation in automotive modules. Features addressed include: input control, overvoltage detection and protection, output on and off open load detection, output short detection, power switching capability, output current limiting and shutdown, output thermal detection and shutdown, dynamic output clamping, and packaging options. Application advantages, performance, and cost trade-offs of each feature are addressed.

An instantaneous power consuming level shifter is presented in this brief to increase the dc converter efficiency. The level shifter is used in a high-side power switch driver to remove the external capacitor which is used in bootstrap technique. The level shifter consumes power only during the transition period. A delay cell is used to turn the level shifter off to reduce the power consumption period. An output voltage detector is added to turn the level shifter off even before the delay time. An asynchronous discontinuous conduction mode buck converter is designed to verify the performance of the level shifter. Simulation results show that the power consumption of the proposed level shifter decreased by 66%, while the converter efficiency increased by the maximum of 9% compared to results obtained for a conventional level shifter. The converter is fabricated using the TSMC 0.18-μm BCD process and it operates within an input range of 2-5 V when the current varies from 400 μA to 18 mA and delivers an output voltage of 1.8 V.

16 - Resonant and Soft-switching Converters

High voltage power MOSFET or IGBT requires a high-voltage gate driver. In this paper, a high voltage gate driver module to drive both the high-side and low-side switching power devices is designed. Both the total volume and parasitic inductance effects of the driver module are decreased considerably compared to the conventional approach of using two packaged single driver chips. A module package is designed and simulated. Two applications are proposed and their typical switching waveforms are simulated.

A new integrated current sensing circuit suitable for step-down DC-DC converters is presented. The current sensing circuit can fully measure the inductor current through sensing the current of power switches whether the high side or low side switch is turned on. The proposed circuits can work in DC-DC converters such that the loading current can be managed through control theories.

This chapter elaborates implementation variants of a buck converter at multi-MHz switching frequencies and input voltages up to 50 V and higher. Implementation aspects of an asynchronous and synchronous buck converter with PMOS or NMOS high-side switch are discussed. The impact on efficiency and the requirements for circuit blocks implementation are derived. A comparison of different switch technologies, in particular integrated DMOS transistors, external vertical switches in silicon and gallium nitride shows that fully integrated switches have at least five times higher switching losses compared to off-chip switches. The influence of PCB routing causes large ringing at the power switches. An optimization of the PCB, including a direct-bond to PCB, significantly reduces ringing. The isolation of a switching high-side domain induces substrate coupling, which results in malfunction of the converter. Various isolation structures to reduce the impact of substrate coupling are examined by both TCAD simulations and by experimental measurements of dedicated test structures.

A level-shifting circuit with sub-nano-second propagation delay for high input voltage switched-mode power converters is presented. The proposed circuit uses isolated low-voltage NMOS transistors and capacitive coupling to shift the control signal of the high-side power switch from a low-voltage logic domain (VLogic ~ 5V) up to a high-voltage power domain (VIN ~ 65V) with less than 115ps propagation delay. As a result, the non-overlap time inserted between the control signals of the high-side and low-side power switches can be minimized, leading to higher efficiency. Moreover, the control signal is shifted to the high-voltage power domain without reducing its voltage swing, which helps minimizing the on-resistance of the switch and further improves efficiency. The proposed circuit is fully integrated in a 0.18μm technology with no off-chip components. It occupies less than 0.75mm2 and provides built-in protection for the low-voltage devices with no additional protection circuitry. Transistor level simulations demonstrate the circuit's functionality and performance.

The operation of a push-pull converter with an input choke and an autotransformer current divider operating in the soft switching mode of all transistors, which is provided by reversing the instantaneous value of the inductor current, is considered. The implementation of the soft switching condition of all transistors, except for reducing dynamic losses on them, leads to an in-crease in dynamic losses in the inductor and static losses in the circuit due to an increase in the effective value of the inductor current. As a result of the experiment, it was shown that an increase in the variable component of the inductor current leads to an increase in the converter efficiency to a certain level of the average inductor current.