Design Of A High Precise Current Sensor For Digital Power Controllers

With the increasement of the variety of electronic products,the requirements for chip performance,especially power management ICs,are more and more demanding.Any electronic product requires a power management chip,especially a high-end electronic device,which requires a high-performance power management chip to for a very robust power supply voltage.Switching power supplies are widely used because of their high efficiency,fast response,and flexible design.In the age of digital,digital switching power supplies have become the mainstream of switching power supplies due to their high integration,high reliability,and short design cycles.In this article,a high-precision current sensing circuit is designed with a self-tuning function based on the digital buck converter.The current sensor is based on the power MOSFET technique.Meanwhile it samples the currents through the high and low side power MOS so that the inductor current can be monitored in real time.This current sensing method consumes less power consumption and has a very high accuracy which theoretically eliminates errors caused by the process and temperature on the sampling accuracy.The designed current sensor has a self-tuning function,which allows the BUCK converter to eliminate the error of the current sensing circuit before use,further ensuring the accuracy of the sensing current.The calibration operation can be repeatedly performed.Compared with the traditional triming,not only the accuracy can be made higher,but also the operation is simpler,the speed is faster,and the cost is greatly reduced.This article firstly introduces the research background and the trend of the development of current sensor.Sencondly,the role of the current sampling circuit in the switching power supply is described.Meanwhile the types of analog and digital current sampling circuits are introduced.Finally,the digital high-precision current sampling circuit designed in this paper is given.Moreover a new self-tuning technology is proposed,which can quickly find the optimal trimming amount.Then according to the requirements of this current sensor,sub-circuits is designed.The last section is the simulation of the current sensing circuit and its self-tuning function.Based on the 0.35 um BCD process,the current sampling circuit and the auxiliary subcircuit are simu lated using Cadence Spectre.The simulation results show that,in the range of 0~10A of the chip output load,the equivalent power of the current smplinp module is from 1.26 mW to 11.7mW.Meanwhile,in the range of 1A ~ 10 A of the inductor current and the full temperature range,the current sampling accuracy of the high-side power transistor is greater than 96% and vast majority is above 99%.The low-side power transistor current sampling accuracy is greater than 93%,and the vast majority is more than 98%.Besides,the self-tuning circuit can quickly find the optimal tuning amount,and the final tuning error is the minimum value of the tuning.