Lithium Coin Cell Charger for Rechargeable Coin Batteries

  • Rajkumar Sharma
  • 13.987 Views
  • easy
  • Tested
  • SKU: EL88004
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This versatile charger has been designed to charge Lithium Coin Cell Rechargeable CR2016/CR2025/CR2032 Coin Batteries. Just insert the battery to the holder, and plug in to any USB port to recharge, D3 Power LED, D1 LED indicates the charge cycle. The board has been designed to use dual chips, either BQ21040 IC from Texas instruments or MCP73831 from Microchip however the board is tested with BQ21040 IC.

Programmable Charge Current using External Resistor up to 800 mA (default set to 50mA), follow the formula bellow to set the desired current.

An external resistor R2 is used to Program the Output Current (50 to 800 mA) and can be used as a current monitor.

RISET = KISET / IOUT

Where

  • IOUT is the desired fast charge current;
  • KISET is a gain factor found in the electrical specification (1)

For greater accuracy at lower currents, part of the sense FET is disabled to give better resolution. Figure 1 shows the transition from low current to higher current. Going from higher currents to low currents, there is hysteresis and the transition occurs around 0.15 A. 

For host monitoring, a pull-up resistor is used between the STATUS terminal and the VCC of the host and for a visual indication a resistor in series with an LED is connected between the STATUS terminal and a power source. First charge after Input supply applied LED will be ON and LED will be OFF when OVP/SLEEP condition.

BQ21040 – Single-Input, Single Cell Li-Ion and Li-Pol Battery Charger

The bq21040 device is a highly integrated Li-Ion and Li-Pol linear battery charger device targeted at space limited portable applications. The device operates from either a USB port or AC adapter. The high input voltage range with input overvoltage protection supports low-cost unregulated adapters. The bq21040 has a single power output that charges the battery. A system load can be placed in parallel with the battery as long as the average system load does not keep the battery from charging fully during the 10 hour safety timer. The battery is charged in three phases: conditioning, constant current and constant voltage. In all charge phases, an internal control loop monitors the IC junction temperature and reduces the charge current if an internal temperature threshold is exceeded. The charger power stage and charge current sense functions are fully integrated. The charger function has high accuracy current and voltage regulation loops, charge status display, and charge termination.

The pre-charge current and termination current threshold are fixed to 20% and 10%, respectively. The fast charge current value is programmable through an external resistor.

Note: The board provides dual option for the charging IC, refer to datasheet of MCP73831 and use appropriate components as per data sheet.

Features (BQ21040)

  • Supply Input 5V USB Port
  • 1% Charge Voltage Accuracy
  • 10% Charge Current Accuracy
  • Low Battery Leakage Current (1 μA)
  • Output Current Approx. 50mA
  • 2-V Li-Ion and Li-Pol Coin Battery CR2016/CR2025/CR2032
  • Over temperature Sensing Protection Through NTC
  • Fixed 10-Hour Safety Timer
  • Status Indication – Charging/Done
  • OUT Short-Circuit Protection and ISET Short Detection
  • 125°C Thermal Regulation; 150°C Thermal
  • Shutdown Protection

Schematic

Parts List

Photos

 

Video

BQ21040 Datasheet

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Nicolas

Hi, Thanks for sharing.
I don’t understand how the led D3 can work. The pin 2 of the CN1 connector should be the ground. On the schematic R4 is connected to the ground? It should be connected to +5V.
Is is an error on the schematic ?

rajeon

Hi,

You are right, its schematic mistake, when i was editing the schematic, it happened, will change and upload again, sorry for inconvenience. but Gerber is ok if you make this project it will work perfectly.

Nicolas

Yes, I know that it work. I seen the video and your work seams very serious. I don’t need the PCB. I was searching schematic examples for a LIR2032 charging circuit. Thanks again for sharing. I also found other examples with MCP73831. The LIR2032 max current is 35mA. I found another schematic with 35mA and I integrated it to my PCB. Your schematic with BQ21040 is given for 50mA… It is ok but maybe too much… The aim is to charge a LIR2032 battery for a RTC DS3231. Chinese module ZS-042 seams to have a lot of problems with charging circuit.

Nicolas

Yes, I know that it work. I seen the video and your work seams very serious. I don’t need the PCB. I was searching schematic examples for a LIR2032 charging circuit. Thanks again for sharing. I also found other examples with MCP73831. The LIR2032 max current is 35mA. I found another schematic with 35mA and I integrated it to my PCB. Your schematic with BQ21040 is given for 50mA… It is ok but maybe too much… The aim is to charge a LIR2032 battery for a RTC DS3231. Chinese module ZS-042 seams to have a lot of problems with charging circuit.

Erik van Zijst

I’m probably misunderstanding something about rechargable LiPo coin cell batteries. Both BQ21040 and MCP73831 charge ICs charge at 4.2V; yet the datasheet of every LiPo coin cell battery I’ve seen (including the battery in the photo: Maxim ML2032) lists 3.0V as the nominal voltage (as opposed to 3.7V) and a charge voltage of ~3.1V (not 4.2V).

Am I looking at the wrong batteries, or am I missing something about the value of the charge voltage in these datasheets? Is it safe to use the BQ21040 and MCP73831 ICs on these batteries?

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