3 Intelligent 3.7V Li-Ion Battery Charger Circuits using Specialized ICs

The post elaborately explains 3 automatic intelligent single chip CC/CV or constant current, constant voltage 3.7V Li-Ion battery charger circuits, using specialized Hi-End IC TP4056, IC LP2951, IC LM3622, with battery temperature sensing and termination facility.

Design#1

CIRCUIT DESCRIPTION

The first design is probably the smartest one, incorporating the IC TP4056 which is a comprehensive constant-current (CC), constant-voltage (CV) linear battery charger IC specially designed for safely charging single cell lithium-ion batteries.

It comes with a  SOP package and hardly any external component count making the IC TP4056 specially applicable for portable Li-Ion charging applications.

In addition, the TP4056 can also work with USB and wall socket based adapter supplies.

This smart design does not depend on any blocking diode due to the presence of an internal PMOSFET architecture which is configured to prevent any sort of negative Charge Current in the Circuit.

A special Thermal feedback loop is included in order to regulate the charge current to limit the body temperature while using in high power operation mode or with high ambient temperatures.

The full charge voltage is fixed at 4.2V, while the charge current can be adjusted externally through a given single resistor.

The IC TP4056 is featured to automatically shut down the charging cycle as soon as the charge current has dropped to 1/10th the set value, after the final float voltage is accomplished.

Some of the other mains features of this IC TP4056 include a built-in current monitor circuitry, an under voltage lockout, an automatic recharge resumption, and a couple of status pinouts to indicate full-charge cut off and the supply input voltage switch ON.

IC TP4056 image and pinout arrangement

FEATURES and SPECIFICATIONS

·Charge Current may be programmed  to a max 1000mA

·The circuit can be free of power devices, Sensing Resistor or a Blocking Diode
·A full fledged Linear Charger in SOP-8 Package for charging applications of Single Cell Lithium-Ion Batteries.

·Designed to Produces a Constant-Current/Constant-Voltage Output

·Capable of Charging Single Cell Li-Ion Batteries through Direct USB Port plugin

·Internally set 4.2V constant Charge Voltage with +/-1.5% Accuracy

·Includes an Automatic Recharge initialization.

·A double LED compatible Charge Status Output Pins for indication purpose

·C/10 Charge Termination or auto shut down feature

·Trickle charge is initiated as soon as a 2.9V threshold is reached.
·An Internal Soft-Start processor Limits and inhibits Inrush surge Current

·Comes with a 8-Lead SOP Package, The Radiator needs to be connected to GND.

ABSOLUTE MAXIMUM RATINGS

Input Supply Voltage(VCC)：-0.3V～8V ·
TEMP：-0.3V～10V
CE：-0.3V～10V
BAT Short-Circuit Duration：Continuous
BAT Pin Current：1200mA
PROG Pin Current：1200uA
Maximum Junction Temperature：145°C
Operating Ambient Temperature Range：-40°C～85°C
Lead Temp.(Soldering, 10sec)：260°C

APPLICATIONS

Cellphones, PDAs, GPS
Charging Docks and Cradles
Digital Still Cameras, Portable Devices
USB Bus-Powered Chargers,Chargers

Pinout specification and functioning details of TP4056 IC

TEMP(Pin 1) :Temperature Sense Input

Hooking up TEMP pin with an NTC thermistor's output in Lithium ion battery pack. If TEMP pin’s voltage goes under 45% or over 80% of supply voltage VIN exceeding 0.15S, this indicates that
battery’s temperature is simply too high or overly reduced, charging at this position is stopped. The temperature detection feature could be disabled by joining the TEMP pinto the ground rail.

PROG(Pin 2): is associated with the Constant Charge Current Setting and may be set by attaching a resistor RI(prog) from this pin2 to GND.

While in the precharge mode, the ISET pin’s voltage is regulated to around 0.2V. and in constant charge current mode, the ISET pin’s voltage is regulated to around 2V. Within all modes and in the process of charging, the voltage on ISET pin could be utilized to monitor the charge current through a meter.

GND(Pin3): Ground Terminal

Vcc(Pin 4): Positive Input Supply Voltage

VIN is the power supply input for the internal circuit to operate. Any time VIN falls at around 30mv below the BAT pin voltage, TP4056 goes into low power sleep mode, reducing BAT pin’s current below 2uA.

BAT(Pin5): Battery Connection Pin.

Link the positive terminal of the battery to BAT pin. BAT pin consumes lower than 2uA current whenever the chip is in the disable mode or in sleep mode. BAT pin offers charge current for the connected battery and presents it with a voltage regulation of precise 4.2V.

(Pin6): Open Drain Charge Status Output, Whenever the battery reaches the Charge Termination shut off point, this pinout is dragged low through an in-built switch, but normally this pin remains in high impedance status.

(Pin7): Open Drain Charge Status Output Once the battery is connected and begins charging, this pinout is taken low by an in-built switch, in any other case the pin is held at high impedance condition.

CE(Pin8): Chip Enable Input. A high input here enables the unit to be in the typical operating mode.

Towing the CE pin to a logic low level will force the TP4056 chip into a disable or shut down mode.

The CE pin is compatible and could be associated wit TTL or CMOS logic triggers.

Li-Ion Battery charger circuit using TP4056

The following design represents the typical Li-ion battery charger circuit with constant current and constant voltage features and with auto termination at 4.2V.

The following figure shows the LED status indication details for the above discussed CV, CC Li-Ion battery charger circuit.

Courtesy: NanJing Top Power ASIC Corp.

Design#2: Intelligent Li-Ion battery charger using  just a single IC LP2951

The following post explains a very simple yet safe Li-Ion battery charger circuit using just a single IC LP2951.

Unlike lead acid batteries one good thing about the Li-Ion batteries is that they can be charged at 1C rate initially. It means the charging current may be as high as the rated AH of the battery at the onset.

The design presented in this article can be used for charging a single 3.7V Li-ion cell or a standard cell phone battery externally at a relatively slower rate.

The diagram depicts a configuration which was used for charging a Li-Ion cell of a portable stereo unit.

The charging specification of the circuit may be summarized as under:

• Maximum charging current = 150mA
• Full charge volt = 4.2V +/- 0.025V
• Charge Current = set at current limit charge mode.

How it Works

In the given circuit the IC LP2951 becomes the main active component which has been specifically chosen because it is capable of delivering an output voltage that's very stable over temperature.

The device also features an in-built current regulation system which limits the output from producing current above the 160mA mark.

Furthermore the IC is entirely short circuit proof and incorporates a thermal shut down facility.

The shown resistor values are precisely selected such that the IC generates an exact 4.2V at its output where the cell is connected.

The trimmer is added for refining the voltage in case there's any discrepancy with the resistor tolerance and ratings.

Initially when the particular discharged cell has a voltage level that's below the 4.2V, the IC  generates maximum current to the cell which is around 160mA as discussed above.

This initial current uplift charges the cell rapidly so that it attains the full charge rated value of 4.2V at an earliest.

Once the terminal voltage of the Li-Ion cell reaches the 4.2V mark, the IC LP2951 instantly inhibits the current so that the battery can longer exceed the 4.2 V level.

The above process highlights the ICs constant voltage regulation capability during the charging cycle.

The big value resistors included in the circuit ensures the "OFF" current drain of the battery to below 2mA, the 330pF capacitor stabilizes the circuit from unwanted noises created at the high-impedance feedback node.

The diode at the output is obviously for preventing the back flow of the battery voltage into the IC in the absence of input voltage.

Design#3: Another Efficient Charger for Li-Ion using IC LM3622

Here we discus a current controlled Li-ion battery charger circuit which has been specifically designed for charging all types Li-Ion Batteries very safely and without any considerations.

It is generally advised that a Li-ion battery should be charged with utmost care and caution as these type of batteries are prone to instant damages or explosions if the specified charging measures are not employed.

Thanks to TEXAS INSTRUMENTS for providing us with this wonderful chip, the LM3622 which is an excellent Li-Ion charger, controller device.

How the Circuit Functions

The IC has been designed for generating a constant current at constant voltage, a basic prerequisite for all Li-Ion batteries. The IC may be configured for charging a single Li-Ion cell or a pack of many.

The circuit using the IC LM3622 can be fed with voltages right from 5 to 24V depending upon the charging needs and the connected battery.

The IC does not require any precision external resistors for implementing the functions. Moreover, the IC has a negligible drain of less than 200nA of current from the battery in the absence of an input voltage.

The in built circuitry of the chip accurately regulates the charging current through the principle of temperature compensated band-gap reference.

The current is regulated, however its done via an external current sensing resistor.The band gap principle results in an efficient operating control performance of the circuit and also of the input supply voltage.

The shown current controlled Li-Ion battery charger circuit illustrates a low drop out linear Li-Ion battery charger design which is capable of charging a single 3.7V Li-Ion Cell.

For enabling low voltage detection, the switches J1 and J2 may be appropriately selected.The IC starts the charging process by first detecting the voltage of the cell and “enable status” of the low voltage detection.

The transistor Q2 immediately comes into the operating condition as soon as the connected battery hits target regulation level, determined by the internal setting of the IC.Q2 now begins supplying a regulated voltage to the connected battery, initiating a constant voltage charging mode of the circuit.

In the above situation the battery receives a constant regulated voltage across its terminals, while the charging current is monitored depending upon the level of charge over the battery. On reaching a full charge condition, the charge current to the battery is significantly reduced to a safe value.

Li-Ion Battery Charger Circuit Diagram using IC LM3622

These were the assorted top 3 smart, intelligent Li-Ion Battery charger circuits for you, if you any more ideas or information regrading such smart designs, please feel free to express them through comments.

About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!