TP4054 is a perfect single-chip constant current / constant voltage linear power management chip for lithiumion batteries.It's portable and small in size Use.What's more, TP4054 is specially designed for USB power  supply specifications.Due to the internal MOSFET structure, external resistance and blocking diode are not  required in application.In high energy operation and high peripheral temperature, the thermal feedback can  control the charging current to reduce the chip temperature.  

The charging voltage is limited to 4.2V and the charging current is regulated by resistance.After reaching  the target charging voltage, when the charging current is reduced to 1 / 10 ofthe set value, The TP4054 will  automatically end the charging process.TP4054 can also be set in the stop working state to reduce the power  supply current to μ A 2 5 . 

TP4054 ensures that the chip will automatically enter the protection state when the battery is connected  reversely, so as to ensure that the IC will not be broken down and lead to battery self discharge accidents.Other features include: charging current monitoring, input low voltage blocking, automatic  recharging and signs of full and start charging.