Design And Research On The Chip Circuit For Buck Swiching Power Supply

Switching regulators have been widely applied in the electronic product field,due to their high integration level,simple peripheral circuits,highly power efficiency.Especially, with the development of the battery-operated portable systems,the switching regulators are becoming an essential building block in the contemporary VLSI systems,replacing the linear voltage regulator with low power efficiency.In the thesis,the market and the development of power manager chip are described, and the technique for buck DC-DC converters is analyzed.After the basic operation principle of buck switching power supply is in detail investigated,the chip circuits of PWM current mode buck DC-DC converters are designed based on buck topology structure.This regulator can generate output voltage as low as 0.8V to 16V with wide input voltage range of 4.75V to 30V.Operating temperature range is 0℃～150℃,and conversion efficiency reaches 90%.Nine sub-block circuits including voltage references,oscillators, error amplifiers,current limiting comparators,sampling circuits,latch,driving circuits, short-circuit protection and over-temperature protection are analyzed and designed.Then several electrical characteristics are simulated and analyzed by using cadence EDA tools. Finally,the whole chip performances are simulated.And the simulation results show the designed circuits can realize the designed targets.The chip has a short-circuit protection function.When the output voltage is lower than 3.75V,the oscillation frequency can be automatically adjusted.The soft-start function can avoid the inductor current overshoot when the chip starts.The slope compensation ensures that the feedback loops in the chip circuit can stability work in the current control mode.The over-temperature protection function can prevent permanent damage because of high temperatures.2um 36V bipolar process and SOP-8E encapsulation are applied.The point measurement and the tests for product application are carried out.The test results show the conversion efficiency approaches 90%under standard load current.When the input voltage is changed from 7V to 30V,the load current will changes 0.6A.When the temperature changes from 20℃to140℃,the load current will change 0.3V.The chip has good voltage adjusting ratio and load adjusting ratio.The designed chip performances basically meet the design requirements.