Research And Design Of BUCK Switching Power Supply Chip Based On Pulse Width Modulation

Power supplies are widely used in scientific research,economic construction,defense facilities,and all aspects of daily life,thus high-performance power ICs plays increasingly important role.The power supply is moving toward high integration,high conversion efficiency,and low power consumption.The step-down switching power supply has replaced the linear regulator due to its excellent performance.At present,the step-down switching power supply chip is the main research direction.Combined with the company's project,a step-down switching power supply chip is designed based on pulse width modulation,including the system design,circuit design and performance simulation verification.The chip mainly includes a bandgap reference,an error amplifier,a comparator,an oscillator and the like.By analyzing the working principle of DC-DC,it can be seen that the current drawn by DC-DC from V_IN is pulsed,and the V_INN fluctuation is large,which may cause the PSRR performance of the internal voltage reference to deteriorate.The sub-linear regulator is used to pre-regulate the voltage reference circuit and the negative feedback network to improve the PSRR.A reference voltage circuit with high PSRR is designed to effectively suppress the power supply noise at the DC-DC output.The error amplifier is designed to operate efficiently during transient operation.The chip also integrates protection circuits such as undervoltage lockout,soft start,and thermal shutdown to monitor the input voltage and temperature of the chip and reduce the inrush current.In the traditional switching power supply,the oscillator frequency adjustment range is small,the control mode is single,and the generated waveform has a long discharge time,which is easy to cause frequency distortion.A frequency-tuned sawtooth oscillator with multi-mode regulation frequency is designed.The sawtooth wave is generated by two capacitor charging and discharging superposition methods,which can hide the discharge process and reduce the discharge time to be close to zero,and the duty ratio is large.With the Cadence EDA tool,the internal module of the chip is simulated and drawn layout with the 0.18?m BCD process.The simulation shows that the input voltage of the chip is 3V to 6V,the wide PWM frequency is adjustable from 280KHZ to 700KHZ,and the maximum output current is 6A.The output voltage is as low as 0.9V.