Pid Compensator Based On-chip High-voltage High-power Buck Converter Design

Step-down switching converter is extensively used in various electronic products instead of LDO due to its high efficiency. Recently, new technical requirements are present in the front of switching converter with rapid development of industrial and automotive power supplies, such as steady operation over wide input-voltage, load and temperature range, simpler design of peripheral circuits and smaller consumption of PCB area.A high voltage and high power voltage-mode Buck converter based on on-chip PID(Proportion Integration Differentiation)compensator is proposed in this thesis, which operates at 300KHz with supply voltage form 8 to 30V and maximum load current up to 5A. Ultimately, the efficiency is as high as up to 87%, the line regulation less than 0.02%/V, and the load regulation less than 0.01%/A. The on-chip PID compensator is implemented by active capacitor and inductor as well as miller capacitor, simplifying the design of peripheral circuits and minimizing PCB area of the whole system; The stability of feedback loop over wide input voltage range is guaranteed by gain compensation in the way of changing the location of low frequency pole in PID compensator; Soft-Start circuit is designed to suppress the inrush current and overshoot voltage during start-up; Besides, the chip can be effectively protected from being damaged under abnormal condition by various protection circuits such as frequency foldback oscillator, hiccup-mode short-circuit protection circuit and smart over-thermal protection circuit.In this thesis, basic operation principles of Buck converter is firstly analyzed, and the theory as well as merits and demerits of PWM/PFM modulation mode and voltage/current control mode are introduced; Secondly, frequency compensation theory of the feedback loop for voltage-mode Buck converter is analyzed, and some important considerations such as efficiency, safety and EMI are pointed out. Then system architecture is analyzed and given according to the requirements of performance demands, and sub-circuits in the charge of author including voltage reference, bias circuit, oscillator with the function of frequency foldback, soft-start circuit, hiccup-mode short-circuit protection circuit, smart overthermal circuit and on-chip PID compensator are completely analyzed and designed based on UMC 0.6-μm BCD process; At the same time, simulation software HISPICE is used to verify the function and performance demands of every sub-circuit above.Finally, main function and performance of the whole system is simulated and validated, and the simulation results meet original design objects well.