Learning of fm4057s single lithium battery linear charging chip

This article will summarize FM4057 The characteristics of the chip 、 And its peripheral circuits , Xiaobai sums up , If there is a mistake , Welcome to discuss .

One 、 Detailed description of pins

1.CHRG: Battery charging display terminal , external LED, Charging is always on , Full of lights

2.GND: The earth

3.BAT: Battery terminal

4.VIN: Charging input terminal

5.DONE: The battery is full at the display end , external LED, Charge and turn off the lamp , Full of constant light

6.ISET: Charging current setting terminal , External resistance

Two 、 Features and their parameters

1. Chip packaging ：SOT23-6

2. Parameters and their ratings

（1） Maximum rating

 （2） Recommended working conditions

3、 ... and 、 Typical application circuits

Attention to detail ：

1. Pattern ： This chip has constant current （CC） Mode and constant pressure （CV） Pattern .

（1） Constant current mode ： External resistance RISET To set

（2） Constant voltage mode ： voltage Generally in 4.2V, No more than 4.3V

If the voltage at the battery end is lower than 3.08V, that FM4057 It will change from high current charging to trickle charging until the battery terminal voltage is higher than 3.08V.

2. Input voltage overvoltage protection

        The input voltage is monitored by an internal comparator .OVP Threshold set to 6.5V（ Typical values ）. When the input voltage exceeds the threshold , The chip activates the overvoltage protection mechanism , Controller output shutdown power MOSFET To prevent the electronic equipment in the handheld system from being damaged due to high input voltage . Of course, it exceeds the withstand voltage value 32V It will still damage , And it's irreversible . When the input overvoltage condition is eliminated , The controller will enable output again by running soft start .

3. electric current

        At the beginning of the charging process, the battery voltage is lower than the precharge Electrical threshold , So the battery starts trickle charging for a period of time ; Then the battery voltage reaches the charging threshold , Start constant current charging , During this period, the charging current is the maximum , The calculation formula is as follows ：ICHG= 3000/RISET(A) ( among RISET Is the external resistance , Typical resistance values can be 3K、5K and 6K.) Its charging current can pass through a Only the external resistance can be set , The charging current configuration is as high as 1A.

Application circuit diagram ：