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How to design Lithium-Ion Battery Charger Circuit using MCP73831

Lithium-ion batteries power the lives of millions of people each day. Due to its lightweight, high energy density, and ability to recharge, this technology is becoming more common in everything from computers and cell phones to hybrids and electric cars. Material handling and airport ground support equipment are also benefiting from these rechargeable batteries.

In this blog, we discuss the tested prototype circuit for a Lithium-Ion Battery Charger that can be used to charge any 3.7V, 500mA Li-Ion battery using a 5V DC power supply (USB, Solar Panel, DC Adapter). A microchip MCP73831/2 IC is used to design the circuit. MCP73831 is a cutting-edge linear charge management controller designed for space-constrained and cost-conscious applications. With customizable preconditioning and charge termination, this IC uses a constant current/constant voltage charge algorithm.

So, let’s have a look at the MCP73831 IC, its features, and how it’s implemented. Miniature Single-Cell Li-Ion Li-Polymer Charge Management Controllers are another name for it.

Introduction to Lithium-Ion Battery:

A lithium-ion battery, often known as a Li-ion battery, is a rechargeable battery made up of cells in which lithium ions travel from the negative electrode to the positive electrode through an electrolyte during discharge and then back again during charging. The outside shell of a lithium battery is made of metal. Because the battery is pressured, the use of metal is especially critical. There’s a pressure-sensitive vent hole in this metal enclosure. This vent will release the extra pressure if the battery ever gets too hot and risks bursting due to over-pressure.  The vent is exclusively for safety purposes. 

Each Lithium battery cell has essentially three components.

  • A Positive electrode
  • A Negative electrode
  • A separator-Electrolyte

Lithium cobalt oxide, or LiCoO2, is used as the positive electrode. Carbon is used for the negative electrode. When the battery is charged, lithium ions flow from the positive electrode to the negative electrode through the electrolyte and attach to the carbon. During discharge, the lithium ions return from the carbon to the LiCoO2.

From the anode to the cathode, the electrolyte transports positively charged lithium ions. The movement of lithium ions causes free electrons to develop in the anode, causing a charge to form at the positive current collector. The electrical current then passes from the current collector to the negative current collector, passing through a powered device (cell phone, computer, etc.). The separator prevents electrons from flowing freely inside the battery.

ADVANTAGES

  • High power density
  • Easy maintenance
  • Continuous voltage
  • Variety of models are available
  • Higher Battery Life
  • Smaller and Lighter
  • Low Self Discharge
  • No Priming

DISADVANTAGES

  • High cost
  • Protection Required
  • Aging
  • Immature technology
  • Safety Concern

Features of MCP73831

Let’s discuss the features of MCP73831 Li-Ion/Li-Po Charger 4.2V, 500mA. Its features are as follows:

MCP73831
  • Linear Charge Management Controller:

– Integrated Pass Transistor

– Integrated Current Sense

– Reverse Discharge Protection

  • High Accuracy Preset Voltage Regulation: + 0.75%
  • Four Voltage Regulation Options: 4.20V, 4.35V, 4.40V, 4.50V
  • Programmable Charge Current: 15 mA to 500 mA
  • Constant Current & Constant Voltage Charge Algorithm with Selectable Pre-Conditioning Charge Termination.
  • Selectable End-of-Charge Control: 5%, 7.5%, 10%, or 20%
  • Constant Current value can be set with 1 external resistor.
  • Automatic Power-Down: Limits Charge Current based on die temperature during high power & high ambient condition.
  • Thermal Regulation: Optimizes the charge cycle time maintaining device reliability
  • Temperature Range: -40°C to +85°C
  • Packaging:

– 8-Lead, 2 mm x 3 mm DFN

– 5-Lead, SOT-23

Applications of MCP73831

Because of its tiny size and excellent energy management capability, the MCP73831 has a wide range of applications in small portable devices. It’s extensively used in the following devices:

  • Lithium-Ion/Lithium-Polymer Battery Chargers
  • Personal Data Assistants
  • Cellular Telephones
  • Digital Cameras
  • MP3 Players
  • Bluetooth Headsets
  • USB Chargers

Pins Description of MCP73831

1. Charge Status Output (STAT)

STAT is a signal that can be connected to an LED to show charge status. For interfacing to a host microcontroller, a pull-up resistor can be used instead. On the MCP73831, STAT is a tri-state logic output, but on the MCP73832, it is an open-drain output.

2. Battery Management 0V Reference (VSS)

Connect to the negative terminal of battery and input supply.

3. Battery Charge Control Output (VBAT)

Connect to the positive terminal of the battery. The drain terminal of the internal P-channel MOSFET pass transistor. Bypass to VSS with a minimum of 4.7 µF to ensure loop stability when the battery is disconnected.

4. Battery Management Input Supply (VDD)

A supply voltage of [VREG (typical) + 0.3V] to 6V is recommended. Bypass to VSS with a minimum of 4.7 µF.

5. Current Regulation Set (PROG)

Preconditioning, fast charge, and termination currents are scaled by placing a resistor from PROG to VSS. The charge management controller can be disabled by allowing the PROG input to float.

Designing 3.7 V, 500 mA Lithium-Ion Battery Charger Circuit

This is the tiny Li-ion/Li-po charger you’ll ever find, small enough to store in any project box. It’s also simple to operate. Simply connect the input contact to any USB port or 5V DC supply, and the output contact to a 3.7V/4.2V lithium polymer or lithium-ion rechargeable battery on the other end.

Li-ion batteries must be charged in a specific constant current/constant voltage (CV-CC) pattern that is specific to this cell chemistry. Overcharging and manipulating a Li-ion cell incorrectly can result in irreversible damage, instability, and even danger!

To keep the battery filled up, charging is done in three stages: first a preconditioning charge, then a constant-current rapid charge, and finally a constant-voltage trickle charge. It works with any size battery and USB port because the charge current is set to 100mA by default. If you like, you may quickly switch to 500mA mode by soldering the jumper on the rear closed, which is ideal for charging batteries that are 500mAh or bigger.

Li-ion Battery Charging Graph

PCB Designing & Ordering Online

If you don’t want to put the circuit together on a breadboard and instead prefer a PCB, this is the PCB for you.

Schematic MCP73831

I built a simple Schematic in EasyEDA. The schematic was then transferred to a PCB. The Lithium-Ion Battery Charger PCB Board looks something like this.

The Gerber File for the PCB is given below. You can simply download the Gerber File and order the PCB from https://www.nextpcb.com/

Download Gerber File: MCP73831 LiPo Battery Charger PCB

Now you can visit the NextPCB official website by clicking here: https://www.nextpcb.com/. So you will be directed to NextPCB website.

You can now upload the Gerber File and place an order on the website. The PCB quality is excellent. That is why the majority of people entrust NextPCB with their PCB and PCBA needs.

The components can be assembled on the PCB Board.

Conclusion:

I hope, this blog helps you to understand how to design lithium-ion batteries Charger Circuit using MCP73831. We will be back with more informative blogs soon.

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