How to Use bq25185 USB DC Solar Charger with 5V Boost: Examples, Pinouts, and Specs

The bq25185 USB DC Solar Charger with 5V Boost (Manufacturer Part ID: 6106) by Adafruit is a highly integrated power management IC designed for efficient energy harvesting and battery charging. It is capable of converting solar energy or USB input into usable power, making it an excellent choice for portable, renewable energy, and IoT applications. The device includes a 5V boost converter, enabling it to charge batteries from low-voltage solar panels or USB sources.

• Solar-powered IoT devices
• Portable battery-powered systems
• Wearable electronics
• Renewable energy projects
• USB-powered devices with backup battery support

1. Power Input: Connect a solar panel or USB source to the VIN pin. Ensure the input voltage is within the range of 2.5V to 5.5V.
2. Battery Connection: Attach a Li-Ion or Li-Po battery to the BAT pin. The charger will automatically manage the charging process.
3. Boost Converter: The SYS pin provides a regulated 5V output. Use this pin to power your system or load.
4. Enable Pin: Use the EN pin to enable or disable the boost converter. Pull it high to enable the output.
5. Charging Current: Configure the charging current by connecting a resistor to the ISET pin. Refer to the datasheet for resistor values.
6. Temperature Monitoring: Connect a thermistor to the TS pin for battery temperature monitoring. This ensures safe charging.
7. I2C Communication: Use the SDA and SCL pins to communicate with the device via I2C for advanced configuration and monitoring.

• Input Voltage: Ensure the input voltage does not exceed 5.5V to avoid damaging the IC.
• Battery Compatibility: Use only compatible Li-Ion or Li-Po batteries with a maximum charging voltage of 4.2V.
• Heat Dissipation: Place the IC on a PCB with proper thermal management to prevent overheating.
• Status Monitoring: Use the STAT pin to connect an LED for visual indication of the charging status.
• I2C Pull-Up Resistors: Add appropriate pull-up resistors to the SDA and SCL lines for reliable I2C communication.

The following example demonstrates how to read the charging status via I2C using an Arduino UNO.

#include <Wire.h> // Include the Wire library for I2C communication

#define BQ25185_I2C_ADDRESS 0x6B // Default I2C address for bq25185

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

  Serial.println("bq25185 Charger Status Check");
}

void loop() {
  Wire.beginTransmission(BQ25185_I2C_ADDRESS); // Start communication with bq25185
  Wire.write(0x00); // Address of the status register
  Wire.endTransmission();

  Wire.requestFrom(BQ25185_I2C_ADDRESS, 1); // Request 1 byte from the status register
  if (Wire.available()) {
    byte status = Wire.read(); // Read the status byte
    Serial.print("Charging Status: ");
    if (status & 0x01) {
      Serial.println("Charging");
    } else {
      Serial.println("Not Charging");
    }
  }

  delay(1000); // Wait for 1 second before checking again
}

• The I2C address (0x6B) is the default for the bq25185. Verify this in your setup.
• The status register (0x00) provides information about the charging state.
• Use pull-up resistors (typically 4.7kΩ) on the SDA and SCL lines for proper I2C operation.

1. No Output Voltage on SYS Pin

   • Cause: The boost converter is disabled.
   • Solution: Ensure the EN pin is pulled high to enable the boost converter.

2. Battery Not Charging

   • Cause: Incorrect battery connection or incompatible battery type.
   • Solution: Verify the battery polarity and ensure it is a Li-Ion or Li-Po battery with a maximum charging voltage of 4.2V.

3. Overheating

   • Cause: Excessive input voltage or insufficient thermal management.
   • Solution: Ensure the input voltage is within the specified range and use a PCB with proper heat dissipation.

4. I2C Communication Fails

   • Cause: Missing pull-up resistors or incorrect I2C address.
   • Solution: Add pull-up resistors to the SDA and SCL lines and verify the I2C address.

Q: Can I use the bq25185 with a 6V solar panel?
A: Yes, but ensure the panel's output voltage is regulated to stay within the 2.5V to 5.5V range.

Q: What is the maximum battery capacity supported?
A: The bq25185 can charge batteries with capacities up to several thousand mAh, as long as the charging current and voltage are configured correctly.

Q: How do I configure the charging current?
A: Use a resistor on the ISET pin to set the desired charging current. Refer to the datasheet for the resistor value calculations.

Q: Can I use the bq25185 without a battery?
A: Yes, the SYS pin can provide a regulated 5V output even without a battery, as long as there is a valid input voltage.

This concludes the documentation for the bq25185 USB DC Solar Charger with 5V Boost. For further details, refer to the official datasheet or contact Adafruit support.