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3.7V Li-Ion Battery Charger Circuit using MCP73831 IC + PCB

Electronic Circuits Thursday, July 15, 2021
Fig.1 - 3.7V Li-Ion Battery Charger Circuit with IC MCP73831


The  MCP73831  device  is  advanced  linear charge  management  controllers  for  use  in  space-lim-ited, cost-sensitive applications. 

The MCP73831 is available in an 8-Lead, 2 mm x 3 mm DFN package or a  5-Lead,  SOT23  package.
Along  with  their  small physical size, the low number of external components required make the MCP73831 ideally suited for por-table  applications.  

For  applications  charging  from  a USB   port,   the   MCP73831   adhere   to   all   the specifications governing the USB power bus.

The MCP73831 employ a constant-current and constant-voltage charge algorithm with selectable precondition-ing  and  charge  termination.  

The  constant  voltage regulation  is  fixed  with  four  available  options:  4.20V, 4.35V,  4.40V  or  4.50V,  to  accommodate  new,  emerging  battery  charging  requirements. The  constant  current  value   is   set   with   one   external   resistor. 

The MCP73831 device  limit  the  charge  current  based on die temperature during high power or high ambient conditions.   

This   thermal   regulation   optimizes   the charge cycle time while maintaining device reliability. Several  options  are  available  for  the  preconditioning threshold, preconditioning current value, charge termination  value  and  automatic  recharge  threshold.  

The preconditioning  value  and  charge  termination  value are  set  as  a  ratio,  or  percentage,  of  the  programmed constant  current  value.  

The  MCP73831  device  is fully  specified  over  the ambient temperature range of -40°C to +85°C.

The Circuit

The circuit is very simple and uses few external components which facilitates the assembly and reduces the assembly cost, the standard charging voltage regulation is normally set at 4.2V, but there are variations in the nomenclature of the last digit of the IC that differentiate them from the standard charging voltage such as:
  • MCP73831-2 = 4.2V
  • MCP73831-3 = 4.3V
  • MCP73831-4 = 4.4V
  • MCP73831-5 = 4.5V
The constant current charging value, is adjusted through resistor 2.2K ohms R3, which in our circuit is programmed for a ~450mA charge. Using a simple formula, we can vary this constant charging current:
Rc = charging resistor
CC = charging current in mA

Formula:
Cc = 1000/Rc

Being our 2.2K resistor, we have:
Cc = 1000/2.2
Cc = ~ 450mA

Remembering that the minimum charging current for this device is 15mA and the maximum current is 500mA.

Lithium Ion Batteries have become popular in large scale in portable electronic devices, due to them having higher energy density compared to other batteries on the market.

Benefits include thousands of recharges and none of the old, well-known "memory effect" problems we had in the first rechargeable NiCd battery cells. 

However, lithium ion batteries must be charged following a carefully controlled constant current (CC) and constant voltage (CV) pattern that is unique to this type of cell.

Overloading and careless handling of a Li-Ion cell can cause permanent damage or instability and a potential danger of explosion.

In Figure 2 below, we have the 3.7V Li-Ion Battery Charger Circuit schematic diagram, with the MCP73831 IC and we can follow and analyze the entire circuit, which is a simple and easy-to-assemble circuit, with few external components.
Fig. 2 - 3.7V Li-Ion Battery Charger Circuit with IC MCP73831

Features

  • Linear load management controller:
  • Integrated pass-through transistor
  • Integrated current direction
  • Reverse Discharge Protection
  • High precision preset voltage regulation: +0.75%
  • Four voltage regulation options: 4.20V, 4.35V, 4.40V, 4.50V
  • Programmable load current: 15 mA to 500 mA
  • Selectable preconditioning: 10%, 20%, 40% or Disable
  • Selectable end of charge control: 5%, 7.5%, 10% or 20%
  • Three-state status output - MCP73831
  • automatic shutdown
  • Thermal regulation
  • Temperature range: -40°C to +85°C
  • Packaging: 5 derivations, SOT-23
  • applications
  • Lithium Ion / Lithium Polymer Battery Chargers
  • Personal Data Assistants
  • Mobile phones
  • Digital cameras
  • MP3 Players
  • Bluetooth Headphones
  • USB chargers

Components List

  • U1 ...................... Integrated Circuit MCP73831
  • LED1 ................. Light Emitting Diode - Red
  • LED2 ................. Light Emitting Diode - Green
  • R1, R2 ............... 240 Ohm Resistors
  • R3 ...................... 2.2K Ohms Charging Program
  • Others ................ Wires, connectors, PCI, tin etc.
We are offering the PCI - Printed Circuit Board, in GERBER, PDF and PNG files, for you who want to do the most optimized assembly, either at home, or if you prefer in a company that develops the board, you can is downloading and make the files in the Download option below.

Files to Download, Direct Link:

Click on the link beside: GERBER, PDF and PNG files

If you have any questions, suggestions or corrections, please leave them in the comments and we will answer them soon.

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My Best Regards!!!

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