Li-ion Battery Charger Circuit Using LTC4056 IC

This guide explains how to build a charger for single lithium-ion (Li-ion) batteries.

It uses a special chip called the LTC4056, which can both limit the charging current and stop charging at the right voltage.

This chip only needs a few other parts to work well.

We will provide instructions and details on how to build this charger circuit.

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

The LTC4056 is a battery charger IC designed specifically for lithium-ion (Li-ion) and lithium polymer (LiPo) batteries.

It offers a compact and efficient solution for charging these types of rechargeable batteries.

Below is a basic outline of a Li-ion battery charger circuit diagram using the LTC4056 IC.

Circuit Description

Parts List:

The LTC4056 is designed to accept an input voltage range between 4.5V and 6.5V.

The circuit is configured to provide a constant output voltage of 4.2V.

Additionally, it can deliver a maximum output current of 700mA.

These parameters are determined by the following formulas:

• 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: this numerical constant is probably used as an estimate or calibration.

Select suitable values for R2 and C2 to achieve the desired charging duration.

Capacitor C1 plays a crucial role in filtering the input supply voltage to ensure stability during the charging process.

The capacitance value of C1 should be chosen based on the specific application requirements and the characteristics of the input voltage source.

An LED is integrated into the circuit to indicate the charging status.

The LED illuminates during the charging process, and when the termination timer times out signifying the completion of the charge cycle the LTC4056 enters a shutdown state.

The ‘CHARG’ pin of the LTC4056 is configured to go into a high impedance state when no input power is present.

This feature helps in preserving the battery and the circuit when there is no power source connected.

Refer to the datasheet of the LTC4056 for additional details and specific component values.

You can successfully construct and operate a Li-ion battery charger circuit using the LTC4056 providing precise control over the charging process for single cell Li-ion batteries.

Construction Steps:

Begin by placing the LTC4056 IC on the breadboard or PCB.

Ensure you connect the necessary power and ground pins to your power supply and ground.

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

Connect the negative terminal to ground (GND) on the LTC4056.

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

There is no need to configure this, it is an inherent feature of the IC.

Connect the PNP transistor between the LTC4056 and the Li-ion battery.

Ensure that the base of the transistor is connected to the output pin of the LTC4056 (check the datasheet for the exact pin configuration).

The PNP transistor will provide the current drive to the battery.

You may need to adjust the base resistor R1 to limit the maximum output current to 700mA, or your desired current, using ohms law:

R1 = V_BE / I_desired

where:

• VBE​ is the base emitter voltage of the PNP transistor (typically around 0.7V).
• Idesired is your desired output current.

Use the resistor R2 and capacitor C2 to program the termination timer according to your desired charging duration.

Calculate the timeout duration T using the formula provided in the previous response:

T = 1.1 × R2 × C2

Select suitable values for R2 and C2 to achieve your desired charging duration.

Connect capacitor C1 to filter the input supply voltage for stability during the charging process.

The value of C1 should be chosen based on your applications specific requirements and the characteristics of the input voltage source.

Connect an LED with a current limiting resistor to indicate the charging status.

The LED should illuminate during the charging process.

When the termination timer times out indicating the completion of the charge cycle the LTC4056 will enter a shutdown state and the LED will turn off.

Ensure that the ‘CHARG’ pin of the LTC4056 is set up to go into a high impedance state when no input power is present.

This feature helps preserve the battery and the circuit when there is no power source connected.

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

The battery will be charged with the configured current and termination timer.

Before deploying the charger thoroughly test the circuit with a battery to ensure that it charges correctly and the termination timer functions as desired.

You can build a functional Li-ion battery charger circuit using the LTC4056 IC.

Conclusion:

It is important to consult the LTC4056 datasheet and application notes for specific details recommended component values, and additional considerations based on the applications requirement.

Always adhere to safety guidelines and specifications of the lithium-ion battery being used.

References

Linear Li-Ion Charger with Termination in ThinSOT