Design Of High Precision BUCK Converter Based On Current Mode COT

BUCK switching converters are widely used in battery-powered fields such as communication equipment,portable electronic equipment,microprocessors,and automotive electronics.Therefore,the design requirements of BUCK converters have become diverse and complicated,one of them is the power supply for driverless cars.The processor inside the driverless car requires a large amount of calculation and processing of driving environment information in a short period of time to ensure the safe driving of the car.It requires that the power supply system can provide a heavy current and have a fast transient response.In this paper,based on the fast transient response and large load current requirements of the driverless cars' power supply,a BUCK converter chip is designed.The typical application scenario of the chip is that the lithium battery inputs 12 V voltage into the chip and then the chip outputs 3.3V voltage to power FPGA.The chip is controlled by current mode COT to ensure fast transient response.It uses type 2 compensation and has good loop stability without slope compensation.The cars contain a large number of electronic circuit units and the noise generated by the switching power supply may affect the normal operation of other electronic units.Therefore,the chip uses a combination of adaptive-on-time and phase-locked-loop to lock the switching frequency to a certain value,which is advantageous to design the noise filter.Considering the voltage drop of the wire caused by the large output current,the chip uses remote differential sampling,which improves the output voltage accuracy and avoids possible oscillations caused by common mode errors between the chip ground and the load ground.In order to improve the integration and reduce the cost,the chip uses an on-chip active equivalent capacitor instead of a large off-chip capacitor as a compensation circuit.Based on the system-level control scheme,this article analyzes the design rules of the module circuit,and designs the circuit structure and performance accordingly,including the error amplifier,dynamic reference,phase-locked-loop,adaptive-on-time timer,and pre-bias current source.It is verified by simulation that the circuits can meet the system requirements.The BUCK converter designed in this paper is based on the 0.35?m BCD process,and the feasibility is verified using simplis and spectre software.The simulation results show that the chip can achieve high-precision voltage output under a wide input voltage range of 5 to 36 V,the output voltage range is 2.5V to 15 V,the maximum load current can reach 20 A,the switching frequency is 200 kHz to 1.2MHz,and the accuracy of phase-locked-loop is better than 1%.