How to Use Adafruit bq25185 USB - DC - Solar Lithium Ion Polymer Charger: Examples, Pinouts, and Specs

The Adafruit bq25185 USB - DC - Solar Lithium Ion Polymer Charger (Part ID: 6091) is a versatile and efficient charging module designed for Lithium Ion and Lithium Polymer batteries. It supports multiple power input sources, including USB, DC input, and solar panels, making it ideal for portable and renewable energy projects. The charger integrates a battery management system (BMS) to ensure safe and reliable operation, with features such as overcharge protection, thermal regulation, and programmable charge rates.

• Portable electronics powered by Lithium Ion/Polymer batteries
• Solar-powered IoT devices and wearables
• Battery backup systems
• DIY renewable energy projects
• Prototyping and development of battery-powered devices

The Adafruit bq25185 charger is built around the Texas Instruments bq25185 PMIC (Power Management Integrated Circuit). Below are the key technical details:

• Input Voltage Range: 3.5V to 17V (USB, DC, or solar input)
• Battery Voltage Range: 3.6V to 4.4V (programmable)
• Maximum Charge Current: Up to 1.2A (programmable)
• Input Current Limit: 100mA to 1.5A (programmable)
• Battery Protection: Overcharge, over-discharge, and short-circuit protection
• Operating Temperature: -40°C to +85°C
• Power Path Management: Supports simultaneous charging and powering of the load
• Interface: I2C for configuration and monitoring
• Dimensions: 25mm x 25mm (1" x 1")

The Adafruit bq25185 charger has the following pinout:

1. Power Input: Connect a power source (USB, DC, or solar panel) to the VIN pin. Ensure the input voltage is within the range of 3.5V to 17V.
2. Battery Connection: Attach a Lithium Ion or Lithium Polymer battery to the BAT pin. Ensure the battery is compatible with the charger’s voltage range (3.6V to 4.4V).
3. Load Connection: Connect your device or load to the SYS pin. The charger will manage power distribution between the battery and the load.
4. I2C Communication: If needed, connect the SDA and SCL pins to a microcontroller (e.g., Arduino) for configuration and monitoring.
5. Thermistor: Optionally, connect a 10kΩ NTC thermistor to the TS pin for battery temperature monitoring.

• Input Source Selection: When using a solar panel, ensure it provides sufficient voltage and current under typical lighting conditions.
• Battery Safety: Use only Lithium Ion or Lithium Polymer batteries with built-in protection circuits to prevent over-discharge or short circuits.
• Heat Dissipation: Ensure adequate ventilation or heat sinking if the charger operates at high currents for extended periods.
• I2C Pull-Up Resistors: Add external pull-up resistors (typically 4.7kΩ) to the SDA and SCL lines if not already present in your circuit.

Below is an example of how to configure and monitor the Adafruit bq25185 charger using an Arduino UNO via I2C:

#include <Wire.h>

// I2C address of the bq25185 charger
#define BQ25185_I2C_ADDRESS 0x6B

void setup() {
  Wire.begin(); // Initialize I2C communication
  Serial.begin(9600); // Initialize serial communication for debugging

  // Configure the charger (example: set charge current to 500mA)
  Wire.beginTransmission(BQ25185_I2C_ADDRESS);
  Wire.write(0x03); // Register address for charge current control
  Wire.write(0x50); // Set charge current to 500mA (example value)
  Wire.endTransmission();

  Serial.println("Charger configured.");
}

void loop() {
  // Read charger status
  Wire.beginTransmission(BQ25185_I2C_ADDRESS);
  Wire.write(0x0A); // Register address for status
  Wire.endTransmission();
  Wire.requestFrom(BQ25185_I2C_ADDRESS, 1);

  if (Wire.available()) {
    uint8_t status = Wire.read();
    Serial.print("Charger Status: 0x");
    Serial.println(status, HEX);
  }

  delay(1000); // Wait 1 second before the next status check
}

1. Charger Not Powering On

   • Cause: Insufficient input voltage or incorrect wiring.
   • Solution: Verify the input voltage is within the 3.5V to 17V range and check all connections.

2. Battery Not Charging

   • Cause: Faulty battery or incorrect configuration.
   • Solution: Ensure the battery is properly connected and compatible. Check the charge current and voltage settings via I2C.

3. Overheating

   • Cause: High charge current or poor ventilation.
   • Solution: Reduce the charge current or improve heat dissipation.

4. I2C Communication Fails

   • Cause: Missing pull-up resistors or incorrect wiring.
   • Solution: Add 4.7kΩ pull-up resistors to the SDA and SCL lines and verify connections.

• Can I use this charger with a 6V solar panel? Yes, as long as the panel provides sufficient current and the voltage stays within the 3.5V to 17V range.

• What happens if the input power is disconnected? The charger will seamlessly switch to battery power to maintain the load.

• Is the charger compatible with LiFePO4 batteries? No, this charger is designed for Lithium Ion and Lithium Polymer batteries only.

• Can I adjust the charge voltage? Yes, the charge voltage is programmable via I2C within the range of 3.6V to 4.4V.