David Chesneau

An Integrated Sliding-Mode Buck Converter With Switching Frequency Control for Battery-Powered Applications

Mobile applications necessitate nowadays huge digital resources. Power management of a digital systems-on-chip is based on dynamic voltage scaling. DC/DC converters used to supply the digital system-on-a-chips are facing stringent constraints with respect to load transients, line transients, and reference tracking. Hysteretic control is known as the most convenient control scheme with a fair tradeoff between transient performances, analog implementation and power consumption. Fixed-switching frequency hysteretic control has been experimented as well as full sliding-mode control. Transient performances are reduced due to latencies introduced in the switching frequency control. A new analog implementation of the sliding-mode control is presented here with switching frequency control using a particular analog phase-locked loop but preserve transient performances. The dc/dc converter is implemented in CMOS 130 nm. The switching frequency range has been voluntarily limited and excludes the possible integration of passive components. A hybrid demonstrator is presented with peak efficiency of 89% at 2-W output power.

Single-Inductor Bipolar-Outputs Converter for the Supply of Audio Amplifiers in Mobile Platforms

Listening music with a headset is now a classical feature of mobile phones. A linear amplifier is still employed to drive the headset as the audio quality must challenge dedicated audio players with somewhat 100 dB of signal-to-noise ratio. This feature must also have the lowest impact on the platform autonomy, size, and cost. A symmetrical power supply is required by such audio amplifiers due to the standard jack connector of headsets. Using an inductive switch mode power supply (SMPS) is the most energy efficient solution to supply audio amplifiers from a battery. Classically, two dc/dc converters are employed to generate the required two symmetrical supply rails from a standard Lithium-Ion battery. It is at the cost of numerous bulky and expensive external components. A solution to reduce the number of external passive components is to consider a single-inductor, bipolar-outputs, (SIBO) dc/dc converter. An early prototype of such a converter has been realized on a 130-nm silicon process and offers primary results, nonoptimal but promising. The feedback control structure is studied based on a small signal model that serves to define the pairing of the loops for designing a decentralized controller. A set of controllers is designed by a pole placement technique and transient performances are demonstrated on audio patterns thanks to a piecewise linear model of the converter. Eighty percent peak efficiency is measured with the primary demonstrator but latter simulation results yield an expected improvement to 90%. The audio specifications appear very constraintful and the proposed SMPS does not meet entirely the latter figures. Limitations are detailed. However, many other applications can benefit from the proposed SIBO dc/dc converter.

Proposal of a low power, 1.6 MHz, 91% efficiency, single inductor, double symmetrical outputs integrated DC-DC converter for CCM and DCM operations

A single inductor, double symmetrical outputs, integrated DC-DC converter with analog control has been designed for supply of low power, output-capacitor-less audio amplifiers. Such amplifiers require positive/negative symmetrical voltage supply for driving headphones without common mode on their output voltages. The power stage of the converter use a single external inductor, 3 external capacitors and five integrated power switches to produce two symmetrical bipolar outputs. This circuit permits to make the economy of using a combination of two separate converters for generating both the positive and the negative output voltage. The benefits are a low number of external components and IOs, and reduced silicon area. The control of the output voltages is accomplished by two feedback loops operating in PWM. A primary prototype has been fabricated in CMOS 130nm process for Continuous Conduction Mode (CCM) and achieves 80% peak efficiency at 360mW output power and 1.6 MHz switching frequency. This prototype validates the simulation results about the analog control strategy and the integration of the whole power stage and control. Improvements are presented in order to increase the efficiency up to 90% at full load. The operation in Discontinuous Conduction Mode (DCM) and Pulse Skipping (PSK) are introduced to improve the efficiency for low output power. The electrical implementation of DCM and some simulation results are presented. Light-load efficiency is improved to around 60%.