Battery charger using LTC4071 charge controller
A very simple Lithium ion battery charger circuit can be designed using the LTC4071 Li-Ion Polymer Shunt Battery Charger System .
Most Li-Ion chargers terminate the charging after a period of time. The LTC4071 does not have a discrete charge termination. Extensive measurements on Li-Ion cells show that the cell charge current drops to very low levels with the shunt charge control circuit effectively terminating the charge. For improved battery lifetime choose 4.0V or 4.1V float voltage.
The internal battery disconnect switch remains off while charging the battery through the body diode of the internal switch until VCC exceeds VLBC_VCC. If the source voltage compliance is not greater than VLBC_VCC, then the battery will never re-connect to VCC and the system load will not be able to run on battery power.
This charger circuit requires only an external resistor to program the charge/shunt current. Assume the wall adapter voltage (VWALL) is 12V and the maximum charge current is calculated as:
IMAX _CHARGE = (VWALL - VBAT _MIN )/RIN= (12V- 3.2V)/162ohms= 54mA
Power dissipated in RIN under full charge current is given by the following equation:
PDISS = [(VWALL -VBAT _MIN )^2]/RIN= (12V - 3.2V)^2=162ohms= 0.48W
The charge current decreases as the battery voltage increases.
The maximum shunt current in this case, with no NTC adjustment is determined by the input resistor and is calculated as:
ISHUNT _MAX = (VWALL -VFLOAT )/RIN=(12V -4.1V)/162ohms= 49mA
At this point the power dissipated in the input resistor is 388mW.
As you can see in the circuit diagram , this electronic charger is very simple to design and require few external electronic parts .