Friday, April 12, 2024

Single-Cell Battery Charging Circuit For IoT Devices

EFY Tested Project

A crucial component in many IoT and wearable electronic designs is the single-cell battery charging circuit. However, implementing this vital element and finding cost-effective design solutions can often be a concern.

This guide presents a selection of circuits with PCB designs for single-cell battery charging, offering practical solutions for your IoT and device design projects.

Single-Cell Battery Charging Circuit
Single-cell Battery Charging Circuit

Battery Charging Circuit – Parts

To design this Single-Cell Battery Charging Circuit, below components are required:

Single Cell Battery Charger Parts
Parts List

Designing 

According to the datasheet of charging IC we have used has the following features-

Battery Charging IC Features
Features of Battery Charging IC

In this context, the circuit is designed to provide a regulated voltage output of 4.20V, ideal for charging 3.3V lithium batteries.

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What sets it apart is its flexibility in offering selectable current outputs ranging from 85mA to 450mA. This current output can be easily configured using just 2 ceramic capacitors and 1 resistor.

Additionally, the circuit allows for the integration of an LED indicator, which can be customized to display the battery’s charging and discharging status according to your preferences.

It’s worth noting that the chip utilized in this circuit comes in two variations: the MCP73811 and MCP73812.

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While both versions provide efficient charging solutions, they differ slightly in terms of the output current. The MCP73811 offers a charge current output of 450mA, whereas the MCP73812 delivers 500mA.

Moreover, you have the flexibility to control and program the output current using the Prog Pin, simply by incorporating a resistor.

MCP73811 and MCP73812 IC's Internal Circuit
MCP73811 and MCP73812 IC’s Internal Circuit
Battery Charger IC Pinout
Battery Charger IC Pinout

Programming the Current Output

As per the IC’s datasheet, you have the capability to program the charging current by manipulating the PROG pin and the corresponding resistor value connected to it.

This means you can precisely determine the current at which your battery will be charged.

Specifically:

  • For the MCP73811, the PROG pin serves as a digital input selection. A logic Low setting corresponds to an 85 mA charge current, while a logic High setting results in a 450 mA charge current.
  • In the case of the MCP73812, the charge current is established by connecting a resistor between PROG and VSS.

To calculate the resistor value required for your desired output current, refer to the formula in the datasheet. This flexibility allows you to fine-tune your charging circuit based on your needs.

Resistor Current Formula
Resistor Current Formula
Single-Cell Battery Charging Circuit PCB
Single-Cell Battery Charging Circuit PCB

If you have any doubt, feel free to ask in the comments below.

Also, check out more such interesting mini-projects.

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