The Design Of Current Mode PWM Controller IC

Switching Mode Power Supply(SMPS) has already obtained widespread applications for its high efficiency, small size and other advantages. Traditional SMPS commonly use voltage-mode PWM technology, but in recent years, current-mode PWM technology has been rapid developed. Compared to the voltage-mode PWM, current-mode PWM has better voltage regulation rate and load regulation rate.The stability and dynamic characteristics of system have also been improved obviously. The internal abilities of current limiting and parallel average current make control circuit become simply and reliable.Based on 1μm high voltage CMOS technology, a high integrated and low power consumption current-mode PWM controller IC is designed in this paper by using Cadence EDA circuit design software and Hspice simulaiton tool.This chip is applied to off-line flyback topology AC/DC power supply module.Based on analysing the basic working principle of SMPS,the whole structure of PWM controller chip is provided in this article. then, all of the sub-module circuits are designed and simulation analysed. At light load or no load condition, the chip will enter Burst control mode which can reduce MOSFET's switching power consumption and high-frequency transformer's core loss, improve power convernsion efficiency and reduce standby power consumption of SMPS system by reduce the chip's working frequency. In order to reduce EMI Radiation Interference, a frequency shuffling circuit is designed which can reduce the peak value of EMI and improve the EMI performance of SMPS system by Fine-tuning the chip's working frequency to change the signal frequency spectrum distribution. As this chip use peak current mode control, when the duty cycle is more than 50%, it exists Sub-harmonic vibration and noise-sensitive issues.So a slope compensation circuit is designed which can avoid the occurrence of harmonic vibration and enhance the stability of the system.At the output stage of the chip, a soft-driver cicuit is designed by using two large size NMOS which make up of totem pole output structure. This tructure have strong drive ability and can drive MOSFET switching directly. In addition,the chip also provides many self-recovery protection circuits,including cycle-by-cycle current limiting protection(OCP), over temperature protection(OTP), over load protection(OLP), over voltage protection(OVP) and under voltage lockout(UVLO).According to the design rules, the layout is designed. The whole layout is checked for DRC and LVS by using Dracula layout verification tools.The final layout area is about 1.4mm ×1.7mm. The chip has been taped out.Test results show that all of the indicators basically meet the design requirements. Its normal working voltage is between 12V and 23V and normal working temperature is between -20℃and 85℃. It has a wide range applications in power adapter, battery charger, TV set-top box and other electronic equipment.