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Study On The Current Mode PWM DC-DC Converter With LDO Embedded

Posted on:2007-01-22Degree:DoctorType:Dissertation
Country:ChinaCandidate:H YuFull Text:PDF
GTID:1102360242461789Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
Portable electronic products require the power supply with less bulk (higher power density), more reliability, higher efficiency and low cost. Apparently, conventional line regulators power is not suitable for the requirements in bulk, efficiency, performance and reliability. However, switching mode power supply (SMPS) are gradually replacing line regulator power by right of little bulk, light weight, low power dissipation and extensive application areas, which becomes mainstream products in the portable electronic devices.The research of DC-DC converter served as the core of SMPS, are becoming a hotspot currently. The technology of DC-DC converter integrates several techniques including theory on the DC-DC converter, Integrated Circuit (IC) design, power semiconductor device technology and so on. At first, the theory regarding with the DC-DC converter system is analyzed and researched in the dissertation before engaging in design of converter chip. The monolithic boost DC-DC converter chip, with constant current output, high frequency, synchronous rectifier and inline low dropout (LDO) line regulator, is then presented by utilizing forementioned research results in the forepart of the thesis.Firstly, based on the system architecture, the principle and key technology of DC-DC converter are introduced and analyzed. Pulse-width modulation (PWM), pulse-frequency modulation (PFM), PWM-PFM and pulse-skipped modulation are introduced in detail afterwards. Compared respectively the advantages and disadvantages in current mode, voltage mode, charge mode or voltage-voltage mode control methods, current mode PWM control is adopted on the DC-DC converter chip.Secondly, on the basis of the current situation and developing trends of modeling of DC-DC converters discussed, a state-space averaging method is put forward to model DC-DC buck and boost converter operating in the continuous conduction mode (CCM). State-space averaging method is employed to derive linear equivalent circuit model of two kinds of DC-DC converter in CCM. Transfer functions are obtained and the steady-state analysis is performed. Based upon these models, general equivalent circuit model and broad sense transfer functions independent of circuit topology are derived, which provided convenience to design control loop and ensure stability of DC-DC converter. By virtue of this, frequency compensation circuit and ramp compensation circuit in the latter chapter are given to solve instability and sub-oscillation problem of current mode PWM DC-DC converter.Thirdly, on the basis of analyzing the cause of switching noise, switching noise model of PWM DC-DC converter is established. Measures of reducing noise during design chip and restraining electromagnetic interference in applying chip were put forwarded.In the fourth, the monolithic boost DC-DC converter chip to drive up to 3 white LEDS, with constant current output, high frequency, synchronous rectifier and inline low dropout (LDO) line regulator, is presented in this thesis. A PWM signal up to 1KHz can be applied to the enable pin to control the LED brightness. The chip is integrated digital interface and 5-bit digital-to-analog converter (DAC), which allows precise digital brightness control. Inline LDO can provide high precision and low ripple voltage output as second output, which introduced technical innovation. Several circuit topology aimed at different sub-block circuit were brought forward to ensure high performance. For example, a super performance bandgap voltage reference with a low temperature coefficient (TC) and high power supply rejection ratio (PSRR), which adopted temperature compensation and current compensation technology, is presented. A novel current sensing circuit is put forward to reduce power dissipation and achieve current comparison cycle by cycle. Several protection circuits are designed, such as over-voltage protection, under-voltage lock, over-temperature and so on.Finally, a typical application circuit is introduced and how to choose periphery devices is discussed in detail. The whole chip simulation results by HSpice are given. Simulation of the whole circuit indicates that the chip has achieved anticipant function and performance objectives.
Keywords/Search Tags:Switching Mode Power Supply, DC-DC Converter, LDO Line Regulator, State-Space Averaging Method, Switching Noise, Pulse-Width Modulation, Current Mode
PDF Full Text Request
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