Cycle By Cycle Detection COT Overcurrent Protection Design

With the rapid development of the quantity and application field of electronic consumer goods, people have put forward higher and higher requirements on the performance indexes of various electronic products. And the buck converter due to its small area, low cost, high conversion efficiency and there are various control modes available to meet the requirement of different concrete conditions of different products, so in a variety of new electronic equipment it has a large number of applications. constant on Time(COT) control mode is what people focus on the study, mainly because the COT control system are simple compare to the other control modes, the circuit has a wide input range and compare to the traditional current control mode, it has a shorter load adjusting time at the same time the COT mode has a better EMI characteristics.Over current protection is a very important part of all protection parts in DC-DC power supply. It is designed to prevent the output current of the chip is too large due to unusual conditions like short circuit, load exceeding. Output current too large will make the power device and load devic overheating and eventually damaged. Based on the Constant on time(COT) control mode, this paper designs a overcurrent protection structure. The circuit detects the current cycle by cycle and enters in hiccup mode after the system confirmes overcurrent to protecting circuit.In this paper, we first introduce the three basic power management techniques, and then introduce the simple working mode of the buck converter, finally analysis the output ripple size when the system in CCM and DCM control mode..Then it introduces the basic method of the system over current protection and the advantages and disadvantages of various protection methods. Then introduce the detection method and the protection method.Finally, in the process of.18μm CMOS we complete the design of the whole circuit, mainly including the reference circuit, over current detection circuit, high speed comparator, timer circuit, soft start circuit. By spectre simulation results show, the circuit can make the inductor current peak and valley value are respectively defined in 5A and 4A after the system overcurrent. And when the system sustained overcurrent 96 cycles the chip will automatically shut off and the dormancy 350μs, then automatically restart. When the system is not overcurrent sustained 6 cycles the overcurrent counter will be cleared.