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As the power required by modern data center processors increases, the power architecture must be adapted; for example, 48 V distribution voltage allows to reduce copper losses by a factor 16 with respect to the use of traditional 12 V power architecture. In order to generate the required processor core voltage, a two-stage approach is usually preferred, where the intermediate bus voltage is generated using an unregulated resonant dc–dc converter as, for instance, an LLC converter. Compared to LLCs, hybrid resonant switched-capacitor converters (ReSCCs) make it possible to achieve large voltage conversion ratios without the need of high turns ratio transformers. In this letter, a novel hybrid ReSCC that performs a 48–3.4 V direct conversion is presented. A prototype of the proposed converter has been implemented, capable of providing a continuous output power of 440 W with a maximum efficiency of 96.3% at 30 A load current. [ABSTRACT FROM AUTHOR]

Inductor current sensing is becoming widely used in current programmed controllers for microprocessor applications. This method exploits a low-pass filter in parallel with the inductor to provide lossless current sense. A major drawback of inductor. current sensing is that accurate sense the dc and ac components of the current signal requires precise matching between the low-pass filter time constant and the inductor time constant (L/R[subL]). However, matching accuracy depends on the tolerance of the components and on the operating conditions; therefore it can hardly be guaranteed. To overcome this problem, a novel digital autotuning system is proposed that automatically compensates any time constant mismatch. This autotuning system has been developed for voltage regulator module (VRM) current programmed controllers. It makes it possible to meet the adaptive voltage positioning requirements using conventional and low cost components, and to solve problems such as aging effects, temperature variations, and process tolerances as well. A prototype of the autotuning system based on a field-programmable gate array and a commercial dc/dc controller has been designed and tested. The experimental results fully confirmed the effectiveness of the proposed method, showing an improvement of the current sense precision from about 30% up to 4%. This innovative solution is suitable to fulfill the challenging accuracy specifications required by the future VRM applications. [ABSTRACT FROM AUTHOR]

This paper investigates the application of a mixed-signal synchronous/asynchronous digital controller to dc-dc boost converters. The digital control synchronously generates current and voltage ramps by using two low-resolution digital-to-analog converters. The switch turn-on and turn-off are determined asynchronously by comparing the converter-state variables and the digitally generated current and voltage ramps. The control features high dynamic performance, frequency modulation during transients, small quantization effects, and low complexity. In order to evaluate the dynamic performance and compare the proposed solution with conventional analog peak-current-mode control, a small-signal model of the synchronous/asynchronous modulation is derived. Even if aimed to an integrated digital controller, experimental investigation has been performed by using discrete components, implementing the digital control in a field-programmable gate array by using a VHDL. The simulation and experimental results on 100-W dc-dc boost converter confirm the proposed analysis and show that the proposed solution enables a dynamic performance that is comparable with that of analog peak-current-mode control. [ABSTRACT FROM AUTHOR]

This paper investigates a mixed-signal fixed frequency digital voltage-mode controller for dc-dc converters. Switch turn-on is determined by system clock, while switch turn-off is determined asynchronously by comparing a signal proportional to the derivative of the output voltage and the voltage ramp driven by the digital-to-analog converter (DAC). One of the most important features is that the derivative action of the proportional-integral-derivative (PID) voltage-mode controller is inherently obtained by a combination of the analog front-end and the hard-wired digital logic, without requiring the numerical computation of the derivative action nor analog reactive elements (capacitors), which are usually needed for the derivative action in the analog domain and which are critical for the IC controller integration. Moreover, as compared to conventional digital approaches based on analog-to-digital converters (ADCs) and digital pulsewidth modulators (DPWMs), the phase-lag due to the uniformly sampled DPWM and due to the output voltage sampling is avoided, thus improving phased margin at the crossover frequency where the derivative contribution is usually prevailing. This property potentially enables faster controllers with improved dynamic response, breaking bandwidth limitation of conventional digital control architectures. The proposed control architecture is also effective from the IC point of view, since it is based on a DAC, a simple analog front-end, including a sample and hold, a comparator and an operational amplifier, and low digital signal-processing requirement (~5000 gates). Simulation and experimental results on a 1.2 V-20 A synchronous buck converter confirm the properties of the proposed solution. [ABSTRACT FROM AUTHOR]

This paper investigates power line communication (PLC) in digitally controlled high-frequency switched-mode power supplies in distributed architectures that share the same bus voltage. Communication between different dc-dc converters is obtained by using switching frequency modulation and by detecting the switching signal on the common supply bus voltage. In case of low power transmission, a small duty-cycle perturbation at half of switching frequency is added to enhance the energy of the transmitted signal. Each converter operates at three different switching frequencies: the first is associated with bit 1 transmission, the second is associated with bit 0 transmission, and the third is associated with no transmission state. In the proposed solution, there is no need for an additional power amplifier in order to inject the communication signal on the power lines, but the signal used for the PLC is inherently generated by the pulsewidth modulation of dc-dc converters. Even if aimed at a dedicated digital IC, the communication architecture has been implemented in field- programmable gate arrays. Simulation and experimental results on dc-dc synchronous buck converters confirm that the performance is achievable by the proposed PLC techniques. [ABSTRACT FROM AUTHOR]

This paper investigates a mixed synchronous/asynchronous digital voltage-mode controller for DC-DC converters. In the proposed control architecture, the turn-on switching event is determined asynchronously by comparing the converter output voltage and a synchronously generated voltage ramp driven by the digital control using a low-resolution digital-to-analog converter. Switch turn-off is determined synchronously by the system clock. In the proposed approach, the derivative action of the proportional-integral-derivative voltage-mode controller is inherently obtained by the frequency modulation, without requiring the digital computation of the derivative action. A simplified small-signal model is also derived in order to analyze the performance achievable by the proposed solution. This control architecture features good dynamic performance, and frequency modulation during transients. Simulation and experimental results on a synchronous buck converter, where the digital control has been implemented in field programmable gate array, confirm the effectiveness of the proposed solution. [ABSTRACT FROM AUTHOR]

This paper proposes a simple autotuning technique for digitally controlled dc-dc converters. The proposed approach is based on the relay feedback method and introduces perturbations on the output voltage during converter soft-start. By using an iterative procedure, the tuning of proportional-integral-derivative parameters is obtained directly by including the controller in the relay feedback and by adjusting the controller parameters based on the specified phase margin and control loop bandwidth. A nice property of the proposed solution is that output voltage perturbations are introduced while maintaining the relay feedback control on the output voltage. The proposed algorithm is simple, requires small tuning times, and it is compliant with the cost/complexity constraints of integrated digital integrated circuits. Simulation and experimental results of a synchronous buck converter and of a dc-dc boost converter confirm the effectiveness of the proposed solution. [ABSTRACT FROM AUTHOR]

This paper describes an innovative digital control architecture for low-voltage, high-current dc-dc converters, based on a combination of current a programmed control and variable frequency operation. The key feature of the proposed architecture is the low complexity: only two digital-to-analog converters (DACs) with low resolution (7-b) are used for control. An original control algorithm is used to reduce quantization effects to negligible levels, in spite of the low resolution of the DACs. Thanks to this algorithm, both static and dynamic output voltage regulation are improved with respect to traditional digital solutions. Adaptive voltage positioning and active current sharing are inherently provided by the new architecture. A detailed description of the control strategy is given with reference to a single-phase buck converter. Extension to multiphase converters is straightforward. The digital control architecture is experimentally verified on a FPGA-based four-phase prototype buck converter operating at 350 kHz/phase. Output voltage tolerance within ±0.5% is experimentally demonstrated, along with negligible quantization effects and fast transient response. The features and the performance of the proposed architecture make it a valuable candidate for the control of next generation voltage regulator modules. [ABSTRACT FROM AUTHOR]

The crossover frequency of DC/DC converters is related to some key dynamic performances such as line and load transient response. In integrated converters, its experimental measurement using standard techniques requires the connection to internal nodes of the controller that are not always accessible to the user. This paper presents a novel integrated loop gain measurement circuit for DC/DC converters with time-based control. The proposed circuit requires only two current-controlled delay lines, a transconductor, and two flip-flops that can be easily integrated with limited area occupation. An analytic description that relates the circuit parameters with the loop gain transfer function is provided along with some design rules for the transistor-level implementation. A prototype of the loop gain measurement circuit has been embedded in a DC/DC boost converter with time-based control designed in a BCD technology with 180 nm CMOS. The circuit has an area occupation of 0.027 mm2 with a current consumption of a few tens of μA. • Loop gain measurement circuit for DC/DC converters with time-based control. • Loop gain measurement circuit can be fully integrated in the converter. • Circuit is bypassed during normal operation saving power consumption. • Implementation requires few simple analog blocks. • Technique works when there are multiple control loops or feedforward paths. [ABSTRACT FROM AUTHOR]