Design Of Buck DC-DC Converter XD1709 With ACOT Control Mode

With the rapid development of integrated circuits,electronic equipments have come out one after another,portable devices such as smart phones have been becoming an indispensable part of our life.Power supply as the core part of the electronic equipments,putting forward higher requirements for the performance of power management ICs.DC-DC converter with its high efficiency,low power consumption and many other advantages is widely used in a variety of electronic products.DC-DC converter has been facing great challenges in order to meet the excellent performances of smaller size,high stability,high reliability and fast transient response of new electronic products.Different control strategies are needed in different application environments for DC-DC converter.Constant On-Time control mode has faster transient response for its simple loop structure than the voltage control mode and current control mode.So it is a great value to research Constant On-Time control technology.However,the drawbacks of Constant OnTime control,such as unstable operating frequency and dependency on the ESR of output capacitance limit its scope of application.It is necessary to solve the above-mentioned problems to achieve higher performance.This paper proposes the Buck converter XD1709 with Advanced Constant On-Time control mode,which has a wide input voltage range of 4.8V~18V,an adjustable output voltage range of 0.765V~8V,700 k Hz operating frequency and maximum output current of 3A.The Advanced Constant On-Time control mode has fast transient response for its simple loop structure and guarantees a stable frequency.On-chip ripple compensation technology adopted is to avoid the subharmonic oscillation phenomenon caused by the low ESR of the ceramic output capacitors,which reduces the difficulty of the application and the cost of the chip at the same time.XD1709 also has a variety of protection modules,including under voltage protection,over voltage protection,over temperature protection,over current protection etc.Besides,the Power Good module allows the state of the power supply to be displayed easily and visually.Firstly,this paper studies the basic theory of DC-DC converter briefly,then analyzes the Constant On-Time control structure based on the Buck converter and sets up the structure of the system according to the functional requirements and characteristics of XD1709.Moreover,design and optimization are carried out for its shortcomings.Finally,the simulation is implemented based on the 0.5?m 5V/24 V BCD process with Spectre simulator by Cadence software.The simulation results show that the proposed system can start normally.The load response is within 10?s during the load current rising from 0A to 3A and declining from 3A to 0A.The output ripple is 6.2m V and the whole system can work stably.Switching frequency keep almost constant with input voltage and load current variation.The efficiency of the chip can up to 92%.All the expected performance has been achieved.