Design Of Lithium Battery Protection Chip Applied To Smart Bracelet

In recent years,with the rapid development of electronic technology and the popularity of mobile electronic devices,lithium batteries are widely used in daily life,especially in portable electronic devices.Such batteries have the advantages of low cost,high capacity and no pollution.However,the use of lithium batteries also exposed certain problems,such as overcharging,excessive current,and so on,which have a negative impact on the performance and service life of the battery,so the demand for lithium electric protection chips has been generated.Therefore,every lithium battery needs a protection chip to ensure the safety and life of the lithium battery.According to the characteristics and actual requirements of lithium battery,a high precision,low power consumption and integrated MOSFET lithium battery protection chip is designed in this paper.The reference source circuit and resistance repair circuit of low temperature drift are installed inside the chip to improve the reference voltage accuracy and then improve the voltage detection accuracy.The over-charge detection accuracy of the chip is ±25m V,and the over-discharge detection accuracy is ±50m V.The MOSFET,equivalent impedance is 50 mΩ,is integrated on the chip.In practical application,only one additional peripheral capacitor can be used.In order to meet the low power consumption demand of the chip,the sleeping mode is set in this chip.The working state of the module is controlled by the clock enable signal.When the chip is in the protection state,most modules will be shut down to reduce the power consumption.In the normal working state,the typical current value is 2.21A.In the sleeping state,the current value is 1.7A.The chip mainly includes a band-gap reference circuit,a battery sampling voltage divider circuit,a voltage comparator circuit,an oscillator circuit,a frequency divider delay circuit and a logic control module circuit.The chip monitors the lithium battery when the charging voltage is too high,the discharging voltage is too low,the working current of the battery is too large or the battery is short circuit.The chip uses 0.5 m BCD manufacturing process of MXIC,and the Spectre software is used to simulate the whole system and each sub-module.The simulation results show that the overcharge detection voltage of the battery is 4.40 V,the overcharge relief voltage is 4.01 V,the overdischarge detection voltage is 2.77 V,and the overdischarge relief voltage is 3.02 V.Through the simulation results,it can be found that the functions covered by the chip run normally and meet the design requirements.