Research And Design Of An Efficient Buck Converter Based On High Voltage BCD Process

With consumers' demands for function and standby time of electronic products becoming more and more picky,power management chips develop in the derection of high conversion efficiency and fast transient response.As a top priority,DC-DC switching power supply is always the hot research topic.For these reasons,a buck DC-DC converter features wide input and output range,large output current,high efficiency over full load current range and fast transient response is researched and designed.The main works are as follows:Firstly,this thesis analyses the topology,modulation mode and control method of the buck DC-DC converter,and focus on the ripple-based constant-on-time(RBCOT)control method.An input voltage feedforward technology is proposed,which makes the RBCOT is in PWM mode at heavy load and PSM mode at light load.Therefore,transient response performance and conversion efficiency over full load range are improved.Secondly,based on the Brokaw bandgap reference circuit,a low temperature coefficient,high power supply ripple rejection bandgap reference circuit is designed.Simulation results show that temperature coefficient of the reference voltage is 2ppm/?,PSRR at 100 kHz is-72 dB.The drawback that LDO supplies the internal power of the DC-DC converer is analysed,and an internal power regulation circuit based on external supply power is proposed in order to further improve conversion efficiency.Thirdly,a timer circuit for RBCOT control is designed,thus making the operation frequency constant in CCM mode.Besides,the timer circuit features adaptive bias current,which reduces the impact of timer's delay itself on timing accuracy.Fourthly,based on 0.35?m 24 V high voltage BCD process,the circuits of the whole chip are finished.Simulation results of the buck DC-DC converter show that the iuput voltage range is 5V-16 V,output voltage is adjustable and ranges from 0.8V to 13 V.It can achieve 5A continuous output current.The conversion efficiency when load current is 0.1A is larger than 85%,and peak efficiency reaches to 95% at large output current condition.The output ripple voltage can be less than 2mV with excellent load and line regulation adopting the ripple compensation technology.The proposed buck DC-DC converter can recover to steady state within one to two switch periods.In conclusion,the indicators meet the design requirements.Finally,aiming at low ripple voltage and noise in regulation power line for high performance analog circuits,a novel LDO with buffer impedance dynamic adjustment is firstly proposed,which can follow the designed buck DC-DC converter to make a simple power management unit.