Single-inductor Multiple-output Converter Research Articles

Voltage‐mode hysteretic control techniques for high‐current single‐inductor multiple‐output switching regulators

In this Letter, two comparator-based voltage-mode hysteretic controller designs are proposed to enhance dynamic response for single-inductor multiple-output (SIMO) switching converters to minimise over-/under-shoot voltages due to self- and cross-regulations in fast load transients, especially with high output power and large current steps. The proposed converters are designed and simulated in a 65 nm CMOS process with standard I/O devices. With the proposed techniques, the output voltage fluctuations, including steady-state voltage ripples and over-/under-shoot voltages due to self- and cross-regulations during a 1.8 A load transient in 1 ns, are kept within 60 mV. The proposed converter delivers more than 3 A maximum load current per output and a maximum total output power above 6 W, with a peak efficiency above 90%. Compared to state-of-the-art SIMO converters, this work achieves a significantly higher output power capacity and faster dynamic response thus smaller self- and cross-regulations within 0.033 mV/mA.

Improved‐efficiency quasi‐two‐stage current‐source‐mode SIMO LED driver

Single-inductor-multiple-output (SIMO) light-emitting-diode (LED) drivers are attractive, practical solutions for lighting applications. An SIMO LED driver is usually constructed with conventional voltage-source-mode dc-dc converters. Current-source-mode (CSM) converters, though being highly suited for current driving, are less studied. Simple control, low cost and independent dimming function are among the advantages of CSM SIMO converters. The limiting factors of CSM SIMO converters, however, include the relatively low efficiency and the restricted number of outputs under low-frequency pulse-width modulation (PWM) dimming control. In this study, an adaptive current bus technique to the CSM SIMO converter is applied. Results show that a significant improvement in efficiency can be achieved. The low-frequency PWM dimming method is also analysed and redesigned. Also, we compare the voltage stress in the CSM SIMO converter with traditional input-series-connected structure. Results show that the CSM SIMO converter achieves a high-voltage step-down ratio without the use of transformers. This study presents detailed analysis and experimental results of the CSM SIMO converter with adaptive current bus.

An 86% Efficiency, Wide-V$_{in}$ SIMO DC–DC Converter Embedded in a Car-Radio IC

This paper presents a single-inductor-multiple-output (SIMO) dc–dc converter suitable for supplying a car-radio. From a single input, an automotive battery-supply ( $\text{V}_{bat}$ ), the SIMO converter generates three regulated output voltages: $\text{V}_{bat}+6.5$ V boost, 4.5 V buck, and 1.8 V floating around half $\text{V}_{bat}$ . A novel, reconfigurable power-stage is conceived and switched appropriately to generate the unique floating output among others. Regulated floating dual-slope (RFDS) drivers are proposed to limit the di/dt through the switches and to reduce the switching-noise. A continuous-time (CT) error-processor is implemented to generate the control-phases. The circuit withstands the 4–40 V range of car-battery variations and regulates in the 4.5–27 V range while remaining in the idle-state outside. The SIMO converter is embedded in a car-radio IC and fabricated in a 110-nm BCD process. The switching frequency is 2.4 MHz. The SIMO converter offers a peak power-efficiency of 86% at 2.7 W of output power and occupies an active area of 2.5 mm2. The operating temperature range is −40°C to +150°C. In a 4-channel car-radio, the proposed SIMO converter reduces the quiescent power-dissipation by up to 36% while having negligible effect on the audio performance.

Circuit Theoretic Considerations of LED Driving: Voltage-Source Versus Current-Source Driving

Light-emitting diodes (LEDs) are solid-state devices with specific $v$ – $i$ characteristics. In this paper, we study the basic requirement of the driving circuits and discuss the proper approach to drive LEDs in view of their characteristics. We compare voltage source driving and current source driving, and discuss their relative advantages and constraints. We specifically introduce the use of circuit duality principle for developing new current-source-mode (CSM) drivers that are less known but are theoretically more versatile compared to their conventional voltage-source-mode counterparts. The study highlights the effects of the choice of driving circuits in terms of the number and size of circuit components used, duty cycle variation, sensitivity of control, nonlinearity and control complexity of LED drivers. We propose a CSM single-inductor multiple-output (SIMO) converter, which demonstrates the advantage of having inductorless and easily controlled current-source drivers, and present a comparison of the CSM SIMO converter with the existing SIMO converters. We further illustrate that a high-voltage-step-down ratio can be naturally achieved by the CSM high-voltage-step-down converter without the use of transformers. This paper presents a systematic and comparative exposition of the circuit theory of driving LEDs, with experimental evidence supporting the major conclusions.

An Analysis of Non-Isolated DC-DC Converter Topologies with Energy Transfer Media

As miniaturized mobile devices with various functionalities are highly desired, the current requirement for loading blocks is gradually increasing. Accordingly, the efficiency of the power converter that supports the current to the loading bocks is a critical specification to prolong the battery time. Unfortunately, when using a small inductor for the miniaturization of mobile devices, the efficiency of the power converter is limited due to a large parasitic DC resistance (RDCR) of the inductor. To achieve high power efficiency, this paper proposes an energy transfer media (ETM) that can make a switched inductor capacitor (SIC) converter easier to design, maintaining the advantages of both a conventional switched capacitor (SC) converter and a switched inductive (SI) converter. This paper shows various examples of SIC converters as buck, boost, and buck-boost topologies by simply cascading the ETM with conventional non-isolated converter topologies without requiring a sophisticated controller. The topologies with the ETM offer a major advantage compared to the conventional topologies by reducing the inductor current, resulting in low conduction loss dissipated at RDCR. Additionally, the proposed topologies have a secondary benefit of a small output voltage ripple owing to the continuous current delivered to the load. Extensions to a multi-phase converter and single-inductor multiple-output converter are also discussed. Furthermore, a detailed theoretical analysis of the total conduction loss and the inductor current reduction is presented. Finally, the proposed topologies were simulated in PSIM, and the simulation results are discussed and compared with conventional non-isolated converter topologies.

Hybrid Control of Single-Inductor Multiple-Output Converters

In this paper, a new control strategy for single-inductor multiple-output (SIMO) converters is proposed. The strategy is based on the hybrid control scheme. Switched linear equations of the converter are used in the design procedure. As a result, the cross regulation is suppressed inherently. A minimum dwell-time constraint is considered to suppress the switching loss and electromagnetic interference. The proposed scheme can control both minimum phase and nonminimum phase SIMO converters. It will be shown that the system is robust to input voltage and load variations. In order to compare the results, a recent pulsewidth-modulation-based control system is considered. Performance of the system is evaluated by a number of simulations and experiments.

A 0.016 mV/mA Cross-Regulation 5-Output SIMO DC–DC Buck Converter Using Output-Voltage-Aware Charge Control Scheme

A single-inductor multiple-output (SIMO) dc–dc converter with output-voltage-aware charge control (OVACC) is presented in this paper. The OVACC scheme reduces the cross regulation by computing the total energy required by all outputs to extract exactly the same amount of energy from the input. Moreover, the proposed design also extends the load capability range of the SIMO converter by supporting the operation in both continuous conduction mode and discontinuous conduction mode while boosting the overall power efficiency. The proposed SIMO (five outputs) dc–dc converter has been implemented in a 0.18 μ m 1P6M CMOS process. Measurement results show that the best cross regulation is 0.016 mV/mA when the output current of 250 mA abruptly changes. And no cross regulation is observed when the first output current changes 150 mA, the second output current changes 160 mA, the third and fourth output currents change 180 mA, and the last output current changes 250 mA. Also, the measured peak power efficiency is 86%.

Current-Source-Mode Single-Inductor Multiple-Output LED Driver With Single Closed-Loop Control Achieving Independent Dimming Function

Single-inductor multiple-output (SIMO) light-emitting diode (LED) drivers have the advantages of being compact, efficient, and low cost. However, the voltage-to-current transfer function of each output of the SIMO converter is not independent, with significant cross regulation issues that necessitate the use of complex closed-loop control for achieving independent dimming function. This paper proposes a current-source-mode (CSM) SIMO dc-dc converter from duality principle, which is shown to be more suited for LED driving due to widened control range of the duty cycle and inherently inductor-less LED driving topology. The outputs of the CSM SIMO dc-dc converter are inherently independent, resulting in very simple control requirement involving only one closed-loop controller for providing the constant current feeder, and several simple open-loop controllers for independent dimmable driving of LEDs. Simultaneous voltage step-up and step-down of multiple outputs is an added feature that simplifies the input power source requirement, especially for portable applications. The whole system is simple, reliable, and low cost. Taking the CSM single-inductor dual-output dc-dc converter as an example, we illustrate the circuit operation and establish a small-signal model for facilitating the design of the feedback control. A direct duty-cycle dimming method is described. Experimental tests are presented for verification.

Single Discharge Control for Single-Inductor Multiple-Output DC–DC Buck Converters

With ever-increasing demand of feature-rich portable electronics, single-inductor multiple-output (SIMO) converters are becoming a cost-effective option to provide different supply voltages while maintaining a long battery life. A single-discharge (SDC) control scheme is proposed to simplify the SIMO design, to achieve low cross-regulation, and to support wide range of loads with reasonable power efficiency. A SDC SIMO buck converter with four outputs composed of comparators, phased-locked loop, finite state machine (FSM) controller, and an output stage, is prototyped using TSMC's 0.18-μm BCD process. In addition to the basic switching functions, the FSM controller provides a state skipping feature to allow no-load regulation. Its functionality is verified experimentally and can convert an input voltage from 2.7 to 3.7 V to 1, 1.2, 1.5, and 1.8 V outputs. The simulated peak power conversion efficiency is 86% with a combined output power ranging from 150 to 300 mW. The packaged SDC SIMO converter ICs exhibit a lower measured peak efficiency of 73%, with a cross-regulation of 0.24 mV/mA due to the parasitic bond-wire resistance. The converter prototype can support a wide range of loading conditions, from open circuit to a total output power of 1 W.

CCM–DCM Power-Multiplexed Control Scheme for Single-Inductor Multiple-Output DC–DC Power Converter With No Cross Regulation

Single-inductor multiple-output (SIMO) switching dc-dc power converter architecture is a cost-effective alternative to multiple individual switching power converters solution in many power distribution system applications where multiple voltage rails are required at reduced cost. However, with multiple output voltage rails coupled to the same switching node, the SIMO power converters suffer from cross regulation between the multiple outputs, which complicates the closed-loop controller design of the SIMO converter and degrades regulation performance. In this paper, a power-multiplexed (PM) control scheme is proposed aiming to completely decouple the operations of multiple outputs from one another. The proposed PM control scheme results in eliminating the cross regulation among the multiple outputs while maintaining desired voltage regulation performance for each output under both steady-state and dynamic operations. Low-cost microcontroller or analog circuitries can be used to implement the proposed controller. Experimental proof of concept prototype results verify the feasibility and advantages of the proposed controller.

Research on a topology of single-inductor multiple-output DC-DC converter with high power conversion efficiency

This paper researches a topology of single-inductor multiple-output DC-DC converter with high power conversion efficiency. Compared with traditional single-inductor multiple-output converters whose output loads are fed only by the energy stored in inductors, the output voltage of this converter is provided by not only the energy stored in inductor but also the energy stored in capacitor. As a result, this converter achieves higher energy conversion efficiency. The circuit description and operation analysis of this converter are displayed and as examples, a single-inductor dual-output and a single-inductor triple-output converter are simulated. The results show that this topology achieves multiple output voltages with high power conversion efficiency.

A Single-Inductor Eight-Channel Output DC–DC Converter With Time-Limited Power Distribution Control and Single Shared Hysteresis Comparator

This paper describes a time-limited power distribution control technique that can be used for single-inductor multiple-output (SIMO) DC-DC converter with many unbalanced loads. Furthermore, the true all-comparator control technique that raises no stability or complexity issues is proposed. This all-comparator technique for SIMO converters is realized only with a single shared hysteresis comparator at a constant switching frequency of 800 kHz. This leads to the development of a new inductor peak-current control technique that does not require compensators and a phase-locked loop. This converter is analyzed and compared with existing SIMO converters with respect to the requirements of next-generation power management ICs. The maximum efficiency of the converter reaches 92%. The fabricated chip supporting eight-channel outputs is implemented in a 0.35-μm CMOS process and occupies an area of 2.4 × 2.1 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Control Scheme for Reduced Cross-Regulation in Single-Inductor Multiple-Output DC–DC Converters

Single-inductor multiple-output (SIMO) dc-dc switching regulators are potentially very good replacement to multiple parallel converters in today's power management units for portable applications where multiple supplies are required. The outputs in these converters being coupled, cross-regulation among the outputs plays a major role in deciding the performance of the system. This paper proposes a control scheme that ensures good load and line regulation and stable system dynamics and reduces cross-regulation effect significantly. In designing a control scheme, proper analysis of the system is an important factor, and SIMO class of converters being driven by a ripple in the inductor current, conventional modeling does not hold good. Consequently, a ripple-based modeling approach that accurately judges the system performance is adopted. A cross-derivative state feedback control methodology has been proposed so as to completely decouple the outputs. Finally, a single-inductor dual-output SIMO converter has been built on a printed circuit board using discrete components, and the test results presented validate the modeling technique proposed. The simulation and experimental results show that the proposed control scheme significantly reduces cross-regulation at the outputs.

Predictive Digital Current Control of Single-Inductor Multiple-Output Converters in CCM With Low Cross Regulation

This paper presents a new digital current-mode control technique for single-inductor multiple-output converters in continuous-conduction mode. This predictive control method can calculate all the required duty cycles corresponding to the outputs for the next switching cycle. Since the calculation is based on every current reference representing the load current, all current control loops corresponding to different outputs are theoretically independent, which can greatly reduce the cross regulation. To avoid subharmonic oscillation, proper predictive digital current control is adopted. Inductor current estimation is used to remove the current sensing circuit, and corresponding calibration techniques are presented. Simulation and experimental results are given to verify the effectiveness of this control technique.

Hardware-Software Codesign of an Embedded Multiple-Supply Power Management Unit for Multicore SoCs Using an Adaptive Global/Local Power Allocation and Processing Scheme

Power dissipation has become a critical design constraint for the growth of modern multicore systems due to increasing clock frequencies, leakage currents, and system parasitics. To overcome this urgent crisis, this article presents an embedded platform for on-chip power management of a multicore System-on-Chip (SoC). The design involves the development of two key components, from the hardware to the software level. From the hardware perspective, a multiple-supply power management unit is proposed and is implemented using a Single-Inductor Multiple-Output (SIMO) DC-DC converter. To dynamically respond to the sensed instantaneous power demands and to accurately control the power delivery to the processor cores, the power management unit employs a software-defined adaptive global/local power allocation feedback controller. The proposed controller is designed using the hardware-software codesign methodology to uniquely control the SIMO converter during various operation scenarios. This is achieved using several embedded software control algorithms that operate synergetically to ensure efficient and reliable system operation. The hardware-software codesign technique also allows the SIMO controller to be integrated with future microprocessor cores. Therefore, by employing the vast amount of on-chip resources, the converter can perform effective power processing to provide the most power-optimal voltages at the hardware level. Such an embedded power management module leads to an integrated, power-aware, and autonomous SoC design that is independent of additional external hardware control, thereby reducing on-chip area and system complexity. In this design, each power output from the SIMO converter provides a step-up/down voltage conversion, thereby enabling a wide range of variable supply voltage. An adaptive global/local power allocation control algorithm is employed to significantly improve Dynamic Voltage and Frequency Scaling (DVFS) tracking speed and line/load regulation, while still retaining low cross-regulation. Designed with a 180nm CMOS process, the converter precisely provides three independently variable power outputs from 0.9 V to 3.0 V, with a total power range from 33 mW to 900 mW. A very fast load transient response of 3.25 μ s is achieved, in response to a 67.5-mA full-step load current change. The design thus provides a cost-effective power management solution to achieve a robust, fast-transient, DVFS-compatible multicore SoC.

On-Chip Single-Inductor Multiple-Output Power Converter Design with Adaptive Cross Regulation and Supply Variation Control for Power-Efficient VLSI Systems

Dynamic voltage and frequency scaling (DVFS) algorithms are widely used power management techniques which enable the optimization of system-level power dissipation, energy consumption and operation performance. One cost-effective hardware-enabling platform to implement the DVFS is through single-inductor multiple-output (SIMO) DC-DC converters. However, the major drawback with such converters is cross regulation, which leads to undesired supply voltage variations. These variations have significant impact on modern VLSI applications, from the circuit to the system level. Based on these challenges, this paper presents a cross-layered design of two SIMO DC-DC converters with an adaptive freewheel switching technique. The proposed converters are able to minimize cross regulation by adaptively adjusting the freewheel switching durations and currents. This also increases the efficiency of the SIMO converters, by reducing the conduction losses due to the lossy freewheel switch. To verify the cross regulation performance of the SIMO converters, its influence on clock frequencies generated by a ring oscillator is investigated. By simulating various load transient conditions, it is shown that the SIMO converters are able to significantly minimize frequency variations. The operation of the converters is verified through transistor-based HSPICE simulation results, with a 130-nm CMOS process. The SIMO converter with the digital-based adaptive freewheel switching controller achieves a maximum efficiency of 93.2%, while the analog counterpart achieves a maximum efficiency of 93.4%. For a load change from 200 mA to 40 mA, the proposed technique reduces the conduction losses during the freewheel switching duration by 99.96%, compared with traditional methods.