| Switching power supplies, be characterize as highly efficient,densely integrated and simply component-used, are widely used in manyfields of electric products. DC-DC Converter is one of the mostimportant parts of switching power supplies which is now most popularin the application of Cars, Computers and Comunication fields.In recent years, the portable electronic products are becoming moreand more popular, which makes a rapid growth of power management IC.With the purpose of providing more functions and high performance, asfar as saving energy, these electronic products need switching powersupply chip with high conversion efficiency as well as low cost.This dissertation proposes a current mode PWM buck DC-DCconverter with synchronous rectification. The chip uses the PWM controlmode to realize its modulation. Besides the traditional architecture and module, a capacitance-sharing-technique is introduced into this chip tosave an off-chip capacitance. A self lift circuit is also added to this chip tomake the switching transistor and the rectifying transistor be NMOS sothat it can save the chip area for its higher mobility than PMOS inconvetional structure. The chip system also includes auxiliary circuitssuch as summing circuit, current induction circuit and protection circuits.This chip is characterized by high converting efficiency, small area andlow off-chip cost with small strike-voltage and surge-current at startingstage due to the soft start module.Spectre simulations are done on each cell and the whole system incadence with the parameter of HHNEC0.35um BCD process. Simulationresults indicate that the output ripple is only2mV, the output precision is0.05%, and the power efficiency is above90%with5V supply voltage,2.5V output voltage and5load resistor. Also in other typicalsimulations, the respective values are achieved. |
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