Li-ion Battery Charger Circuit using IC LTC4056

The article discusses how to build a Li-ion (single-cell) battery charger.

The LTC4056 is a special chip that uses to limit the charging current and stop charging at the right voltage.

This chip just requires few circuit parts to function correctly.

The construction of this charger circuit is described in detail.

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

An IC LTC4056 are designed specifically for lithium-ion (Li-ion) and lithium polymer (LiPo) batteries

It provides a small and effective solution in terms of charging various types of rechargeable batteries

An LTC4056 IC based Li-ion battery charger circuit schematic is shown in the simple way 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 parameters:

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

Resistor R2 and Capacitor C2 in the circuit serve as essential components for programming the termination timer.

The values of R2 and C2 can be selected according to the desired timeout duration T.

The timeout duration can be calculated using the following formula:

T = 1.1 × R2 × C2

where,

• T is a time duration.
• R2 represents an ohm based resistance value.
• C2 is a capacitance value expressed in farads.
• 1.1 is numerical constant probably used as an estimate or calibration.

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 R2 and C2.

To maintain stability during charging process 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 characteristics 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:

The following are the steps for building a Li-ion battery charger circuit with an IC LTC4056:

First place the LTC4056 IC onto the PCB or breadboard.

Make sure your power supply and ground have the correct power and ground pins connected.

Connect the LTC4056s input voltage pin (Vin) to the positive terminal of your power supply.

Connect the negative terminal to ground (GND) of LTC4056 IC.

A constant output voltage of 4.2V is exactly what the LTC4056 is made to do when charging a Li-ion battery.

This function is incorporated into the integrated circuit and does not require configuration.

Between the Li-ion battery and the IC LTC4056 connect the PNP transistor.

Check the datasheet for the exact pin design to make sure the base of the transistor is connected to the LTC4056s output pin.

The batteries current source is derived from the PNP transistor.

Using ohms law, if needed modify the base resistor R1 to limit the maximum output current to 700mA or your 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 your desired output current.

Set the termination timer to the length of time you want it to charge using the resistor R2 and capacitor C2.

Using the formula given previously calculate the timeout length T:

T = 1.1 × R2 × C2

To get the charging period you require use the right values for R2 and C2.

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

The particular needs of your application and the properties of the input voltage source should be taken into account 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 state when the termination timer shows the charge cycle is completed.

Make 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.

Make sure 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 appropriate component values 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