A Used In Step-down Dc-dc Converter, Lcd Driver Circuit Design

With the development of the display monitor, the power management ICs for LCD is in great demand. In order to meet the market requirement, a PWM controlled step-down DC-DC converter is designed in this thesis. It is based on UMC 0.6μm BCD process. With wide input voltage range from 4.5V to 28V, an output voltage down to 3.3V can be generated. An internal linear regulator provides the supply voltage for the whole chip. The low-cost, all N-channel, synchronous topology enables operation with efficiency as high as 93%. It uses a current-mode control architecture, providing fast load transient response and easy compensation. A novel current-limit circuit which carrying the PSM function can protect the power supplies against fault conditions. Furthermore, high frequency (250kHz or 500kHz selectable) allows easy filtering and faster loop performance. Soft-start can limit inrush current during startup. This converter can operate in the temperature range from -40℃to 85℃. It is well suited for LCD Monitor and TV applications running directly from AC/DC wall adapters.In this thesis, basic principles and some key points of the buck power stage were given firstly. Then, the whole chip diagram was proposed according to the design specification and the whole chip operational principle was introduced. Based on the whole chip function requirements, sub-block design and simulation were completed. Since the chip was accomplished through the team work, the author payed particular attention to the analysis of the whole chip architecture and the design of the following sub-blocks, including enable controller, oscillator, slope compensation and current sense. At last, the whole chip function simulation and typical performance characteristics simulation were presented. In the conclusion of this thesis, the research value of this circuit was pointed out, but it was suggested that corner simulation and post-layout simulation should be indispensable.This thesis is a production of circuit principles and simulation practice. Based on the circuit principle analysis, the author simulated the sub-block circuits and the whole chip circuit by applying the EDA tool HSPICE. The simulation results indicated that the IC has achieved the expectation, both function target and electrical characteristics. The basic principle of Pulse Width Modulation on step-down DC/DC converter is testified, and this effort accumulates more experience to design step-down DC/DC converters with more perfect performance for the future.