Full-custom design of a current-mode controlled DC-DC converter chip for smart system applications

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Dr. Takács Gábor
Department of Electron Devices

DC-DC converters are the means of generating stable source voltage for supply sensitive elements, such as smart system circuitry and micro sensors, actuators. They are capable of stabilizing the voltage of an unstable power source and making it independent of the load, which is critical for the changing load conditions of micro devices.

In case of grid type smart systems the power sourcing also needs to support the scalability of the system. Beside traditional batteries and other wired sources novel techniques, such as Power-over-Ethernet, RFID provide functional elements with wide range of unregulated supply voltage. This thesis work introduces the design of a switched mode step down DC-DC converter chip which can create stable output voltage from such wide range of input voltage regardless of the type of the source, capable of operating with both buck and flyback structures.

This thesis work compares the industrially applied control modes and methods, realizing adaptive constant off-time current mode control to fulfill the specified requirements of high efficiency, good small signal behavior, immunity to current mode instabilities, and peak current control on 0.5μm high voltage CMOS technology. AC model of the converter is also discussed to achieve the proper dynamic behavior. In addition, corners simulations are executed to examine the device operation in design corners. Then the layout design of the analog circuit blocks is carried out. Finally, the results of the efficiency simulations are compared with similar industrially available chips.

The outcome of the thesis is the full schematic level design of a general purpose buck/flyback converter together with the layout of the analog circuit blocks.


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