Research And Design Of Buck DC/DC Converter With LDO Mode

With the increasing popularity and rapid development of electronic products, therequirements for power supply which is used in various electronic equipment andsystems is more and more harsh. Switching DC/DC converter with its high efficiency,stable output power, low ripple, high integration and other advantages, is widly usedin various portable electric devices. Now, switching power supply is moving towardhigher conversion efficiency, smaller size, higher reliability, modularization andhigher integration.In the first, this thesis introduces the basic principles of switching power supplyDC/DC and linear power supply, studies existing related technology of Buck DC/DCconverter deeply, then analyses various kinds of the power losses of the DC/DCconverter and modulation methods, builds model for voltage loop and current loop ofDC/DC converter and analyse its stability. From the switching power supplyapplications needs in portable devices, after suming up the strengths and weaknessesof existing technology, it takes advantage of that LDO has low quiescent current andlow ripple output voltage at light load, through system design, circuit design andperformance simulation, and achieves a peak current mode Buck DC/DC converterwith LDO mode.In the key circuit design, considering control circuit of typical summation circuitis complex and depends on process, this thesis proposes a novel ramp generating andsumming circuit based on switched-capacitor, which enhances precision of samplingvoltage amplifer, ramping generate and summation, and also reduces circuitdependent on process. After analyzing the strengths and weaknesses of existingcurrent sampling techniques, it designs a high accuracy current sampling circuit byadding the current compensation current. This circuit eliminates the need for amplifier,simplifying the circuit structure, while the introduction of compensating currentimprove the current sampling accuracy up to99.9%.Finally, this thesis realizes the circuit this thesis designed based on0.5um CMOSprocess, verifies and simulates every sub-circuit module and the overall circuit usingsoftware of Hspice, Spectra, Simplis, etc, the results show the DC/DC converter canapply for portable devices and meet the design requirements.