Research And Design Of A Synchronous CC/CV Buck DC-DC Converter

With the rapid development of electronic and electric power technology, the increasing of the type and quantity of the portable handheld devices, integrated power management system has been widely used in communications, computer, consumer electronics and other fields. High frequency, miniaturization, integration has become the major trends in power management chip in the future, and how to meet to maintain stability over a wide range, large fluctuations in input voltage, low output ripple, timely response to load changes and adjust accordingly and to ensure that the switching power supply to reduce their power consumption while improving their conversion rate requirements has become a key chip research and design.In this paper, a Buck DC-DC converter with constant current and constant voltage control is designed on the basis of the working principle, modulation mode, current loop stability and voltage loop frequency compensation of the step-down DC-DC. The input voltage range of the chip is 8.5~36V, the typical value is 12 V, the output voltage range is 1.2~28V, the typical value is 5V, the maximum load current is 9.6A, the work frequency of the converter is 225 k Hz, By using synchronous rectification technology, the external integrated N type power switch tube and the N type continued flow pipe simplify the design of the system circuit and reduce the drive loss, conduction losses and the chip area. This paper proposes a novel constant current start control circuit controls the output current through an external resistor, Compared with the traditional start-up circuit, the inductive current can quickly rise to a constant peak in a few cycles, and the output voltage can quickly rise, so the load carrying capacity of the starting process can effectively guarantee. By using PWM/PFM hybrid modulation mode, when the output current is large chip in PWM modulation mode, when the output current is smaller chip enters PFM mode, in this mode, when the chip goes into sleep mode, off-chip most module, retaining only the basic module to reduce static power consumption, improve the efficiency of the chip light loads. In the chip, the 5V voltage of the input voltage can be transformed into a premodulation circuit of the chip, which reduces the static power consumption of the chip integrates over temperature protection, overvoltage protection, undervoltage shutdown and other protection module and improve the work efficiency. Under normal operating conditions,the conversion efficiency can reach up to 94%, thus saving the cost and reducing the extra cost.In this paper, a standard 0.35?m BCD process is used for the constant current and constant voltage control. The Spectre simulation environment is used in the Cadence software platform at different process corners and different ambient temperatures, and the whole function of the core module and the system is simulated. From the simulation results, the function of constant current control is realized. The chip is suitable for vehicle charger/adapter, portable charging equipment, general CC/CV charging application and so on. The chip has been taped out, is being tested.