| In recent years, with the large-scale expansion of portable electronic devices such as MP3, iPhone, mobile phones, PDAs, digital photo albums, electronic books..., the kind of smaller size, higher efficiency, lower power consumption and lower-cost electronic products become more and more popular among manufacturers and customers. At the same time, integrated circuit design become more and more complex, which put forward higher requirements especially for power management. With the continuous supply voltage reduction and the overall power consumption of portable devices falling, switched-capacitor (SC) DC-DC converters with the supply capacity within 500mA have become the mainstream power management solution for portable devices.Switched-capacitor DC-DC converters, which only use capacitors as energy transfer medium, compared to inductor-based converters, not only save more PCB area but also have less electromagnetic radiation (EMI) problems. So SC converter is more preferably applied to noise-sensitive electronics products. However, switched-capacitor converters compared with inductor-based converters, the output voltage ripple is more larger, usually tens of millivolts. The efficiency of SC converter is among inductor based converter and LDO. This paper has not only effectively improved light load efficiency, but also clamped the output voltage ripple within 10mV by technical means. Also the switching frequency is predictable, so the switching noises can be eliminated by filter, which making switched-capacitor DC-DC converters become the best alternative product to replace LDO.By using the input current limit control (Current limiter) and adaptive clock duty cycle modulation (ADCM), the SC converter proposed by this paper effectively reduce the output voltage ripple. Light load efficiency is also improved by automatically selecting a lower clock frequency which is achieved by using adaptive frequency modulation (AFM). Due to a negative feedback loop existing in the system, this article has proposed an appropriate frequency compensation network after system analysis and modeling to ensure the system stable in the entire input voltage and load current range. In order to improve overall system efficiency, this article has analyzed various power losses such as gate drive loss, conduction loss, slow switching loss and current source drop-out loss in order to determine the optimal switching frequency and optimal transistor sizes. After finished circuit and layout design, the proposed switched-capacitor DC-DC converter is manufactured by Chartered 0.35μm 2P4M CMOS process. Test result shows: the system peak efficiency is up to 87%, and the maximum output voltage ripple is less than 8mV, and also, the converter has a good line regulation and load regulation performance by using a new proposed compensation network, which has achieved the desired requirements. |
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