Design And Analysis Of Trimming Solutions For A High-performance Switching Mode Power Supply Chip

For the analog circuit, once it has emerged from wafer processing, the character is established that can not be changed. However, some of the parameters do not meet the design expectations due to processing and other non-ideal environmental factors, this fact result in that the accuracy and performance of the chip after processing fall far short of expectations. In order to bridge the existing gap between circuit design expectations and final product performance, several trimming technology for monolithic ciriuit have been developed in recent years. At the same time, SMPS(switching mode power supply)chip also develops with higher performance, higher precision, lower costs. Therefore,developing appropriate means of trimming for SMPS chips is very essential.The main purpose of this paper is to design trimming solutions according to the chip characteristics which is based on a SMPS chip design project.Firstly, the principles, function and some common methods of trimming technology are introduced. After that, this paper gives a brief introduction of the chip’s characteristics, the internal structure and common application. According to the characteristics and structure of the chip, this paper has designed trimming circuit for the susceptible parameters.For this chip, two different trimming solutions have been presented.The fist solution is a metal fuse trimming solution.The advantage of this solution is low cost and good process compatibility. This paper completes the circuit design, and verifies the correctness of the circuit through imitating fuse status for circuit simulation.The metal fuse trimming is completed before packaging, so it can’t avoid the effects caused by packaging. Therefore, This paper presents another solution —Zener diode anti-fuse trimming solution. This trimming technology is implemented after packaging which means more precise. However, this trimming solution usually only use the existing pins which are designed for users. According to this feature, this paper uses the only six functional pins to design the trimming circuit. In this solution, the article also designed a "previewing trimming" circuit for some important parameters, that is,simulate the relevant parameter change if the fuse status changed, without damaging the fuse.Through this progress, we can detect the best combination of trimming, then the corresponding fuse will be trimed. Through the functional simulation, it verifies thecorrectness and feasibility of the circuit design.At the end of this paper, the two trimming solutions are compared. Both of the two solutions have their advantages and disadvantages. The specific selection should balance the factors of process conditions, accuracy, cost, etc.