Design And Implementation Of The High-precision Seven-cell Lithium Battery Protection Chip

Since lithium batteries has the features of small size,high energy density,no memory,many cycles and low-carbon environmental protection,it has become the most widely used rechargeable batteries in portable electronic devices,and its application gradually covers the fields of smart home appliances and electric vehicles.However,during the working process of lithium batteries,abnormal conditions such as overvoltage,overcurrent,and overtemperature may appear,which will reduce the working efficiency,service life,and even cause dangerous of combustion,explosion and so on.Therefore,a corresponding protection circuit for the lithium batteries is particularly important.According to the practical application requirements of lithium batteries,this paper designs a high-precision protection chip for seven-cell lithium batteries.The designed protection chip includes a bandgap reference module,a voltage detection module,a current detection module,a delay module,a cascade module and a driver module.Reference voltage provided by the bandgap reference module to other detection modules;The voltage detection module detects the voltage of each battery individually when an abnormal voltage occurs in one of the batteries,the protection chip will protect all the batteries;The current detection module sets a multi-segment current protection mode to detect the charge and discharge current;We can adjust the delay time of various protections through the delay module,and output logic control signals to the drive module;The charge and discharge circuit of the battery string can be controlled by the switch of the charge and discharge integrated off-chip MOSFET tube through the drive module.Functionality of the chip is verified through the simulation analysis of the entire working state,the layout design and test of the actual chip.Compared with similar products at home and abroad,the protection chip designed in this paper uses a low temperature drift reference circuit and trimming technology to improve the reference voltage accuracy,thus achieving the high accuracy of the protection chip,the voltage detection accuracy is ?25mV.An inter-chip cascade circuit based on the diode principle is designed.The cascade circuit has a simple structure.This chip can detect and protect seven lithium batteries.Fewer chips can be cascaded to detect and protect more lithium batteries in the practical applications so that we can cut the costs.In addition,it also has two-position charge overcurrent protection function and a custom function of protection delay time,which is more complete.The design and simulation of the entire protection chip is based on Shanghai Huahong Grace's 0.8 ?m HV process,and is verified using the Spectre software of the Candence platform.The simulation results are consistent with the expected design requirements and the functionality of the chip is complete.The test results show that the maximum error between the overcharge protection voltage and the preset value of 4.25 V is-19 mV,and the maximum error between the overdischarge protection voltage and the preset value of 2.70 V is-16 mV,which meets the requirements of high-precision voltage detection and cascade function.