| With the rapid development of the electronic information industry,electronic products are becoming more and more inseparable from people's daily lives.At the same time,the functions of electronic products are also becoming more diverse.Electronic products such as Smart phones,smart bracelet,tablet computers,and laptop computers have gradually become the necessities of our daily lives.People are increasingly demanding the portability and high efficiency of these electronic devices,and the market is increasingly demanding for power supply performance.However,traditional power supplies often use linear power supplies,which are inefficient,bulky,and narrow in input range.Switching power supplies emerged as a result.DC-DC power supplies in switching power supplies are widely used because of their flexible voltage conversion methods.The DC-DC power supply adopting the new control mode becomes stand out.Aiming at the problems of low efficiency of existing power management chips,the slow response speed and the inadjustable output voltage,this paper designs a high efficient and practical synchronous BUCK DC-DC regulator based on the constant on-time control mode.The main research results are as follows.1.A DC-DC regulator with a wide input voltage range(2.7V~30V)and output current up to 6A using COT mode control is designed,and the output voltage is adjustable(0.8V~13.2V).The PWM-controlled input feedforward ensures fast transient response over the entire input voltage range.In addition,the error amplifier and loop compensation are not required in the COT control mode,which shortens the transient response time.The switching frequency can be controlled up to 1MHz by the external program.2.A timer structure with a minimum on-time limit module is proposed.The minimum on-time limit module is added to limit the minimum pulse width to 146.6ns by using the principle of NOR gate being determined by the high signal.The minimum on-time module and the timer module can work together to shield the interference signal,filter the pulse,enhance the chip's immunity and reliability.3.Improved PWM/PFM hybrid modulation method.By setting the MODE pin to select the modulation mode,the forced PWM mode and the PWM/PFM free switching mode are selected according to the signal level of the MODE pin.After entering the PWM/PFM free switching mode,according to the load detection circuit,the PWM is selected under the heavy load condition and the PFM is selected under the light load condition.It can maintain high efficiency in the large load range,and the chip efficiency can reach 90%.Even at the low duty cycle of 24 V to 1.05 V,the efficiency can reach 75%.4.A new type of packaging is used.The analog circuit,the main switch tube,and the freewheeling tube are respectively packaged with three dies,which reduces the mutual interference.The analog circuit and the main switch tube are placed in the VINP area,and the freewheeling tube is placed in the LX area,which saves the bonding wire from the upper tube to the VINP and the lower tube to the LX,thereby reducing the wire resistance.5.Design layout,sample testing,production process.The voltage regulator also has multiple protection functions,such as under voltage latch,loop current limit,output overvoltage protection,short circuit protection,and thermal shutdown.Based on the 0.25 um BCD technology of UMC,the chip selected Cadence,Hspice D,and other EDA tools for circuit simulation,layout design,and tapeout verification.The Tektronix,Rigol,and other companies' oscilloscopes,power supplies,multimeters and other tools were used to measure the samples.The rated operating temperature of the environment is:-40 C ~85 C.The simulation and test results show that all the parameters of the chip meet the design requirements. |
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