The scope of this master thesis was to introduce and implement, a new concept
for adaptive (dv/dt control) control of the slope of the switching node voltage in
DC-DC Buck converter. The DC-DC Buck converter applications are becoming
part of many SoC (System on Chip) applications because of their characteristics
and performances. Some valuable features of the Buck converters are their
high-efficiency factor, the small number of external electronic components and small
area. The before mentioned features are the main reason why Synchronous Buck
converters are used in many low-voltage automotive SoC applications.
The main focus of this thesis was to create an adaptive control over the slope
of the switching node voltage in DC-DC converter, which is using several types
of external transistors from dierent vendors. The two main requirements were
to keep the switching frequency high (in order to achieve high efficiency) and
to reduce the conducted EME (Electromagnetic Emissions) generated from the
switching activity of the Buck converter. There are many existing techniques
for reducing the electromagnetic emissions like EMI-lters, special PCB design
techniques etc., that can be used to minimize the EME of the power converter
application, but in our approach our goal was to reduce the conducted EME during
the design. The third important requirement was to have adjustable control
driver that can control a synchronous DC-DC Buck converter which can use several
dfferent types of the external MOSFET devices. This means that the control
driver should work properly for all chosen external MOSFET devices.
Considering the requirements we have implemented an adaptive driver control
which should provide a reduction of the EME and improve the eciency. The
solution presents a Mixed-Signal design. It employs a control logic, which needs
to be implemented as a digital logic block, and an analog part, which needs to
be implemented with programmable driver and analog delay block.
The work of this master thesis is divided into several chapters. First, we will
highlight some important topics from the EMC (Electromagnetic Compatibility)
and why it is important to design a product that satisfies the international regulations
concerning EMC standards. In Chapter 1 we will also explain what the
sources of the Electromagnetic emissions in Integrated circuits are, especially in
the Switched Mode Power Supply applications like Synchronous Buck converter.
In Chapter 2, we will introduce two proposed concepts that were investigated
in this master thesis work which full the given requirements. Also, some comparative
analysis of the already existing concepts and the proposed ones
will be given. Chapter 3 describes the implementation of the necessary blocks
which are needed for the proposed concepts. The proposed concepts are consisting
of Control Logic block and Adaptive Driver block. The connection between
the control block and the adaptive driver is achieved with a Level Shifter which
adapts the voltage levels between the control block and the adaptive driver. In
this chapter, the implementation of the Adaptive driver block and Level Shifter
block will be given. The implemented blocks will be presented together and their
functionality will be checked in the concept's test bench.
Out of the control block, an FSM (Final State Machine) state diagram will be
created and presented here. It will be used in the future work for the Digital
design. At the end of Chapter 3, the spectrum diagrams for the electromagnetic
conducted emissions are presented. Some comparative analysis of adaptive
switching mode (including the proposed concepts) and hard switching mode of
the synchronous Buck converter were also given. At the end, the conclusions and
further future work will be given.
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