| With the rapid development of technology, the good performance of the power management chip is becoming more and more important, in particular, switching power supply chips with high efficiency have been be gradually applied to a variety of battery-powered portable digital devices, such as mobile phones, PADs, PDAs and other hand-held devices. Power management chips are paying more attentions to high efficiency,low-power dissipation and green-used. As a result, the power management chips with high performance, low dissipation, slight interference turn out in competitions, and also get a pretty favor. Based on the background, combine with scientific projects, a high performance asynchronous Buck DC-DC converter is designed and implemented.Based on detailed analysis of the basic principles and the PWM control-mode of Buck DC-DC converters, an asynchronous rectified Buck DC-DC converter is designed. By using the peak current control mode, the transient response has been improved efficiently,and the double poles of the output inductance have been eliminated. Thus it is easy to design the control loop. The PWM modulate mode is introduced in the converter, in the case of fixed frequency, the modulation of output voltage is achieved by changing the Duty cycle. The structure of external circuits is easily established, the output ripple voltage is rather small and has a good linearity. In order to prevent sub-harmonic when the duty cycle is beyond 50%, the chip adds slope compensation circuit internally, which can well improve the stability of the circuit controlled by peak current. The chip owns circuit which generates standard reference voltage, and further optimize the accuracy of the reference voltage reference by the addition of high-temperature compensation, so that it is able to eliminate the influence on the internal module because of external input voltage fluctuation effectively, which is not only improve the performance of the circuit, but also reduce the dissipation. The system has over-temperature protection circuit, adding a hysteresis to prevent occurrence of accidental reversal, which can limit the operation temperature efficiently, and protect the circuit from burning out. Adding cycle-by-cycle current limiting,the chip detects the current flowing through the inductor, which can protect the inductor from burning out by reason of over-current. In the over-current state as well as dead-short chip will enter hiccup mode, effectively preventing the damage to the chip during the failure. Based on PFD, CP, VCO, a synchronous clock module is designed to make sure the chip can be synchronized to a given clock effectively. A relatively simple soft start module is implemented to prevent the converter output voltage from overshooting to achieve a smooth start of the output voltage during start-up. In addition, multifunctional circuits are integrated in the chip, such as UVLO, Over-voltage protection, bootstrap. The fixed frequency is as high as 420 k Hz, which makes the size of the external components smaller comparatively.The asynchronous Buck DC-DC converter with high performance and precision is based on 0.6um BCD process with the basis of Cadence software platform, the entire circuit is simulated with Spectre simulation tools. The range of output voltage is 4.5~30V, and the maximum of load current is 5A, besides, the maximum of conversion efficiency of the chip can be as high as 95%. |
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