| The switched capacitor DC-DC converter using capacitor as energy storage element can provide better power density and smaller volume than the switched inductor converter,so it is more attractive in low-power or area limited applications such as portable electronic equipment.In order to ensure the stable operation of the equipment for a long time and improve the system efficiency of the switched capacitor converter chip,it has become the current research One of the hot spots.At the same time,because the switched capacitor system in PWM,PFM and other modulation modes has a closed loop,there are stability problems,so the stability analysis of switched capacitor converter system has become the focus of current research.Based on the above discussion,a high efficiency switched capacitor converter with wide input voltage range is designed in this paper,The main work is as follows:(1)A reconfigurable switched capacitor array is designed,which is based on the series parallel topology and consists of two flying capacitors and nine switches.By changing the working state of the switch,four kinds of voltage ratio can be achieved: 1/1,2/3,1/2 and 1/3,so that the system can maintain high efficiency in a wide range of input voltage;(2)The dual-mode control strategy of PFM and burst is designed for the switched capacitor buck converter.Under heavy load,PFM mode is adopted,and the output voltage ripple of the converter is small;under light load,the system enters burst mode,when the output voltage is higher than the rated voltage,only the capacitor supplies power for the load,which further improves the conversion efficiency of the system,and the ripple is also in the relative burst mode Relatively large;(3)By using charge balance method and Z-transform,the small signal model of the discrete-time system is established,and the stability of the loop is analyzed.By introducing a zero point to compensate the frequency of the loop,the stability of the switched capacitor converter system under full load is guaranteed.The circuit is designed and simulated by HHGrace 0.35μm BCD process.The simulation results show that when the input voltage range is 1.6～4.0V,the output voltage is 1.0V and the input voltage is 3.2V,the maximum load can be 200 m A;when the input voltage is 2.2V and the load current is 40 m A,the peak efficiency of the converter can reach 87.3%;when the system is in burst mode,the maximum static current is 63.2μA. |
