A Power Management Chip Protection Circuit Design

With the development of LCD industry, the synchronous progress of related industry makes the demand of TFT-LCD controller and driver IC increase rapidly. To meet the market requirement, a step-down converter and its protect circuits are researched in this thesis. The converter which has wide input voltage range from 4.5V to 28V is based on UMC 0.6μm BCD process. Current mode control architecture brings fast load transient responds and simple compensation network. All N-channel, synchronous topology enables operating efficiency as high as 93%. This converter which operates over the -40℃to +85℃temperature range is well suited for LCD monitor and TV applications running directly from AC/DC wall adaptors. The protect function is incarnated in four aspects. The usage of soft start avoids the damage probability brought by inrush current during startup period; a novel current limit can protect the power supplies against fault conditions; the usage of over temperature protect (OTP) protects IC from the damage brought by temperature; under voltage protect (UVP) makes sure that the IC doesn't work in under voltage situation.Basic principles and typical Buck converter topology were given first in this thesis. Then, the whole chip diagram and sub-circuits of protection were proposed according to the principles mentioned before. Since the chip was accomplished by a team, the author took charge of the whole chip analysis, sub-circuits'design which included UVP, soft start, OTP and current limit. The protect function's realization and typical performance characteristics of the whole chip were validated through simulation. In the conclusion of this thesis, the research value of this circuit was pointed out, and 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 design expectation, both function target and electrical characteristics. The principle of DC-DC converters and its protect circuits described in this thesis provided a reference for more superior and universal protect circuit of power management ICs.