Li-ion Battery Charger Circuit using IC LTC4056

In this blog we will discuss how to build a Li-ion (single-cell) battery charger circuit.

The IC LTC4056 is a special chip which controls the charging current and shuts off the charging at the right voltage.

For this IC to function correctly we have just used some of the circuit components.

The construction of this charger circuit is given in details through this article.

What is a Li-ion Battery Charger Circuit using LTC4056 IC:

IC LTC4056s are made especially for batteries that use lithium-ion (Li-ion) and lithium polymer (LiPo).

It offers a compact and efficient way to charge several kinds of rechargeable batteries.

The circuit design for a Li-ion battery charger based on an LTC4056 IC is shown simply below.

Circuit Working:

Parts List:

The IC LTC4056 can handle input voltages ranging from 4.5V to 6.5V.

A constant output voltage of 4.2V is supplied by this circuits design.

The maximum output current it provides is 700mA.

The formulas mentioned below calculate these factors:

• Input Voltage (Vin): 4.5V ≤ Vin ≤ 6.5V
• Output Voltage (Vout): 4.2V
• Maximum Output Current (Iout): 700mA

The circuits resistor R2 and capacitor C2 are important components for controlling the end time of timer.

The desired timeout period T is used to figure out the values of R2 and C2.

The following formula is used to calculate the timeout duration:

T = 1.1 × R2 × C2

where,

• T is a period of time.
• R2 is a resistance value based on ohms.
• The capacitance value C2 is given in farads.
• The numerical constant 1.1 is most likely an estimation or speculation.

Two essential parts of the circuit for setting up the termination timer are the resistor R2 and the capacitor C2.

The value of R2 and C2 are calculated using the necessary timeout period T.

The timeout duration is calculated using the following formula below:

To get the required charging time use the right values for resistor R2 and capacitor C2.

To maintain stability during charging process the capacitor C1 is essential for filtering the input supply voltage.

While choosing the capacitance value of C1 care is needed for a particular applications requirements as well as the features of the input voltage source.

To indicate the charging status an LED is included inside the circuit.

The LED lights up during charging and the LTC4056 goes into a shutdown mode when the termination timer goes off showing charge cycle is completed.

The LTC4056s CHARG pin is designed to enter a high impedance condition in the absence of input power.

In the absence of a power source this feature helps in protecting the circuit and battery.

Refer to the IC LTC4056 datasheet for specific part values and further details on the IC.

The LTC4056 easily controls the charging process of single cell Li-ion batteries making it possible to effectively build and run a Li-ion battery charger circuit.

How to Build:

Below are the steps for constructing a Li-ion battery charger circuit using an IC LTC4056 which are as follows:

First connect the LTC4056 IC to the breadboard or PCB.

Verify that the correct power and ground pins are connected to the power source and ground.

Connect the positive terminal of the power supply to the input voltage pin (Vin) of the LTC4056.

On the LTC4056 IC connect the negative terminal to ground (GND).

While charging a Li-ion battery the LTC4056 is designed to provide a constant output voltage of 4.2V.

There is no setting needed for this function because it is built within the integrated circuit.

The PNP transistor is connected between the Li-ion battery and the IC LTC4056.

Verify that the transistors base is connected to the LTC4056s output pin by consulting the datasheet for the exact pin design.

The PNP transistor provides the batteries current source.

If necessary adjust base resistor R1 using ohms law to limit the maximum output current to 700mA or the desired current:

R1 = V_BE / I_desired

where:

• VBE​ is the base emitter voltage of the PNP transistor which is around 0.7V.
• Idesired is the desired output current.

Select the termination timer to run for the amount of time needed to charge the resistor R2 and capacitor C2.

Calculate the timeout length T using the earlier provided formula:

T = 1.1 × R2 × C2

To get the charging period one requires to use the right values for R2 and C2.

For consistency throughout the charging operation connect capacitor C1 is required to filter the input supply voltage.

The particular needs of the application and the properties of the input voltage source should be taken into mind when selecting the value of C1.

To show the charging state connect an LED to a current limiting resistor.

While charging the LED should light up.

The LED will turn OFF and the IC LTC4056 will enter a shutdown mode when the termination timer shows the charge cycle is completed.

Be sure the LTC4056s CHARG pin is configured to enter a high impedance condition in the absence of input power.

When no power source is connected this feature helps protect the circuit and the battery.

Connect the PNP transistor to the single cell Li-ion battery.

The selected current and termination timing is used to charge the battery.

Ensure the charger charges correctly and the termination timer works as expected by carefully testing the circuit using a battery before installing it.

The IC is used to construct a working of a Li-ion battery charger.

Conclusion:

The LTC4056 IC based Li-ion battery charger circuit provides a simple, reliable and effective way to correctly charge single cell Li-ion batteries.

It is important to refer to the LTC4056 datasheet and application notes for exact details on right component values and as well as extra factors based on the needs of the application.

Strictly follow the lithium-ion batteries safety instructions and standards.

References:

Linear Li-Ion Charger with Termination in ThinSOT