Charge Pump Based On PFM Control Strategy

The market of portable electronic products grows rapidly which challenges the design of power management circuits. The new requirements of dc to dc converters are lower power, smaller volume, faster response and smaller ripple. Power management includes three parts: switched inductance dc to dc converters, switched capacitor dc to dc converters and LDO(low dropout regulator). LDO is the linear regulator. The efficiency of LDO is much lower than the switched converters. The switched converters include the switched capacitor and switched inductor converters. And the switched capacitor is much better choice than the switched inductor converter at the hundreds of load current condition because the magnetic components have bigger volume and higher EMI.Based on deep understanding the power stage characteristics of the charge pump and researching of different control strategies of charge pumps, for example, the voltage mode, the current mode and the traditional PFM(pulse frequency skip mode). We proposed a new frequency regulation (FR) to regulate the output voltage and reduce the voltage ripple. FR mode improves the efficiency and reduces the ripple voltage compared with the conventional fixed frequency control strategies in light and middle load conditions. FR mode just likes the traditional PFM mode to improve the efficiency in light load condition.The Proposed FR mode is an innovation because it has improved the efficiency and ripple voltage than the traditional methods. Another innovation is to achieve the small signal model of power stage about frequency variation. This model can be used to support theory analysis for the system stability of FR mode charge pump. So far, the paper about it has not been published.In this paper, Chapter one introduces all kinds of the power stage topologies of the charge pumps. In chapter two, various control strategies are introduced and we present the FR control strategy. In chapter three, the small signal model of power stage is derived. In chapter four, the block circuits are designed and discussed, including EA, VCO, Dead-zone, power stage, Hysteresis comparator and Digital logic. In chapter five, the FR control strategy theory is analyzed; design and simulation results of the system are given.The block circuits of the charge pump are implemented in TSMC standard 0.35um process. Simulation results showed the system and circuit work well . All the expected specifications were realized.