Research On Li-ion Battery Voltage Detection Circuit Based On High-bit Prediction Strategy

Nowadays,successive approximation analog-to-digital converter(SAR ADC)is widely applied in battery management system to achieve A/D conversion function.During the charging or discharging process of Li-Ion battery pack,there will be a lot of redundant conversion steps in the traditional working mode of SARADC because the voltage of single battery is very close and changes slowly.Based on the voltage characteristics of Li-Ion battery,a high-bit prediction strategy based on SAR ADC is proposed in this paper,which can reduce the conversion steps of ADC effectively to save ADC conversion time and reduce ADC power consumption.Based on the high-bit prediction strategy of SAR ADC,the mathematical analysis is carried out in this paper.The relationship between the saved conversion time and the battery pack parameters,such as the number of battery,cell number for high-bit prediction,standard deviation,change rate of digital number is obtained.The relationship is verified by behavioral simulation.Under the guidance of this mathematical analysis,this paper chooses the optimal control strategy,and designs a voltage acquisition and readout circuit based on multiplex switches and level shift.The main modules include multiplex switches,level shift,SARADC based on high-bit prediction strategy and low drop-out regulator.In this paper,a battery management system based on high-bit prediction SAR ADC strategy is designed based on 0.25 ?m 1-poly 5-metal BCD high-voltage process,where the power consumption of SAR ADC is reduced from 1.76 m W to 1.09 m W.In consideration of the practical application of electric vehicle,this design detects the voltage information of 10 series Li-Ion batteries,and adopts the predictive strategy based on 8 batteries.The input voltage range of single battery is 0?4V,and the total input voltage of battery pack is 10?40V.The chip can measure all the battery voltage information in the system in 2ms.Compared with the traditional SAR ADC strategy,in a ?=10,f = 5k Hz,N = 10 and CN = 8 system,the proposed strategy can save 27.83% of the ADC conversion time in the charging processa nd 27.89% of the ADC conversion time in the discharging process when the lithium ion battery with a single capacity of 1.1Ah working at 25 ? and 1.1m A current.