Study And Design Of A Boost DC-DC Converter XD1415 With Constant Current Output Function

Based on the scientific research project of Key Lab of High Speed Circuit Design and EMC Ministry of Education in Xidian University " Theoretical research on the key technique and the design for deep-submicron mixed signal ASIC", a Boost DC-DC converter XD1415 which has the function of constant current output is proposed in this paper. Compared with conventional DC-DC converters, the function of constant current output is fully new kind of function. Converter XD1415 can realize the function of constant current output without complicated off-chip circuit, and the function of constant current output can improve the load range of the converter greatly and cost savings.Traditional converter will be shut off when the output current up to the current value of over-current protection due to the limitation of the function of over-current protection. In order to improve the output load range, the converter described in this paper use the function of constant current output to limit the maximum output current. Converter XD1415 is mainly used in portable electronic devices such as mobile phone, PAD, and mobile power supply. Converter XD1415 can provide stable and continuous output for portable electronic devices and extend the life of battery with the characteristics of high efficiency and high integration. Converter XD1415 simplifies the external components by using synchronous rectifier.The paper firstly introduces the development of integrated circuit technology, and the commonly used DC power suply technology(LDO, Charge Pump and DC-DC convertor) also is introduced simply. And then several kinds of topology structures of DC-DC converter(Boost DC-DC, Buck DC-DC and Buck-Boost DC-DC) are analyzed. According to the topology structure of circuit, the critical condition between continuous conduction mode and discontinuous conduction mode is deduced. The different ways of the internal control of DC-DC converter(voltage mode, peak current mode, average current mode and hysteresis current mode) is introduced in detail, the PWM and PFM also are introduced in detail. And then the technical specifications of the converter XD1415 is introduced in detail, and the architecture diagram of control part of the loop of the converter XD1415 is also shown. The specific operating mode of current loop which achieve the function of constant current output are analyzed in detail. Theconverter XD1415 adopts peak current mode control and PWM modulation, and on the basis of the peak current mode circuits, a current loop to realize the function of constant current output is added. When the load current reaches a certain value, the convert er XD1415 keep the output current constant by reducing the output voltage gradually. The value of output current in constant current output mode can be adjusted by the external resistance. The working frequency of the converter XD1415 is 800 k Hz, functions of soft start, over temperature protection and over-current protection are integrated inside the convertor. Then some module circuit of the converter XD1415 are analyzed in detailed, it involves enable module, UVLO module, frequency generator module, the average current sampling module, the slope compensation module, GMI amplifier module and VREFX module, and the simulation results and analysis is also given. These are the core modules of the control part of converter XD1415, their performance directly affect the final performance of the converter. Finally the waveform of full chip simulation results of the converter XD1415 is shown. Results show that the converter XD1415 can realize the constant current output function. The converter work in constant voltage output mode when the output current is less than the set current value of constant current output mode. The converter work in constant current output mode when the output current is bigger than the set current value.The system and module circuit of the converter XD1415 is described in this paper, based on 0.5um BCD(Bipolar, CMOS DMOS) process, each module and the whole system are simulated by using Cadence and Hspice simulation tools. The simulation results show that the converter XD1415 can meet each performance indicators and it can achieve the function of constant current output correctly.