Research And Design Of Wide Input CC/CV Step-down DC/DC Chip

As more and more portable electronic devices into our daily lives,the performance requirements for electronic devices are constantly improving, this is also a strong impetus to our researches and innovations on power management unit. Wide input range, high efficiency, strong loading capacity and strong anti-jamming ability have become the main index of power management unit. Therefore researching how to improve the performance of these indexes under the premise of not affecting other indexes has become a major research direction in today’s switching power supply designs.This paper made a deep research into the working principles of buck DC-DC converter and designed a wide-input sensorless CC/CV step-down DC-DC converter on this basis. Using the peak current-PWM control mode, the difficulty of loop compensation can be reduced and the transient response capability to the loads can be improved effectively. The BURST modulation will be used in light-loading and it will improve the efficiency. This paper presents a novel constant current control mode, the current of CC mode can be set by the value of the external resistance, which improves the accuracy and controllability of output current and saves the area of chip, and reduces the disadvantages of traditional current sense methods. Designs a effective circuit of output cable resistance compensation, according to the relationship between output current and the output voltage of EA, the decrease of output voltage caused by the drop voltage of the output wires has been depressed and the accuracy of the output voltage has been improved in this way. In addition, the chip also integrates cycle-by-cycle current limit, soft start, thermal shutdown, short circuit, overvoltage and undervoltage circuit to ensure the normal work of the chip.The paper first describes the development trends of the switching power supply and the significance and purpose of this subject, then introduces the topology structure and working principles of the switching power supply, and then research the influence to stability of the voltage loop and the current loop by the zero-poles of the switching power supply and discusses some problems about the peripheral device selection. In the end, several important sub-modules and the layout design rules have been introduced.Based on 0.35 um BCD process model, the whole chip and its sub-modules have been designed and simulated by Cadence spectre and the layout designs and the function tests of the chip are completed. The input voltage range of the converter is 10 V ~ 40 V, the maximum output voltage is 12 V, the maximum output current is 3A. Under the normal condition, the work frequency of the converter is 225 KHz, the efficiency can reach 94%, which meets the design requirement. This chip is suitable for car charger/adaptor, rechargeable portable devices, general-purpose CC/CV supply and so on.