How to Use BQ25185 USB DC Solar Charger with 5V Boost: Examples, Pinouts, and Specs

The BQ25185 USB DC Solar Charger with 5V Boost (Adafruit Part ID: 6106) is a highly integrated battery management IC designed for efficient solar charging applications. It supports USB input, solar panel input, and features a 5V boost output to charge batteries or power external devices. This component is ideal for portable, low-power, and renewable energy projects.

• Solar-powered IoT devices
• Portable battery-powered systems
• Wearable electronics
• USB-powered battery charging
• Backup power systems

The following table outlines the key technical details of the BQ25185:

The BQ25185 IC has multiple pins for power input, output, and control. Below is the pin configuration:

1. Power Input: Connect a USB power source or a solar panel to the VIN pin. Ensure the input voltage is within the range of 3.5V to 6.5V.
2. Battery Connection: Attach a single-cell Li-Ion or Li-Polymer battery to the BAT pin. The IC will manage charging automatically.
3. Boost Output: Use the BOOST pin to power external devices requiring 5V. Ensure the load does not exceed 1A.
4. System Output: The SYS pin provides power directly from the battery or input source, depending on availability.
5. I2C Communication: Connect the SDA and SCL pins to a microcontroller (e.g., Arduino UNO) for advanced configuration and monitoring.

• Use a decoupling capacitor (e.g., 10µF) between VIN and GND to stabilize the input voltage.
• Place a resistor on the ISET pin to set the desired charging current. Refer to the datasheet for resistor values.
• Monitor the STAT pin to determine the charging status. Connect it to an LED for visual feedback.
• Ensure proper heat dissipation if operating at high currents for extended periods.
• For solar panel input, use a panel with an open-circuit voltage within the supported range (3.5V to 6.5V).

The following example demonstrates how to monitor the charging status of the BQ25185 using an Arduino UNO:

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

#define BQ25185_I2C_ADDRESS 0x6B // Default I2C address of the BQ25185

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

  Serial.println("BQ25185 Charger Monitoring");
}

void loop() {
  Wire.beginTransmission(BQ25185_I2C_ADDRESS);
  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

    // Check the charging status bits (refer to the datasheet for bit definitions)
    if (status & 0x01) {
      Serial.println("Charging in progress...");
    } else if (status & 0x02) {
      Serial.println("Charging complete.");
    } else {
      Serial.println("No charging activity.");
    }
  }

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

1. No Output Voltage on BOOST Pin

   • Ensure the EN pin is pulled high to enable the IC.
   • Verify that the input voltage is within the specified range (3.5V to 6.5V).
   • Check for proper connections and ensure the load does not exceed 1A.

2. Battery Not Charging

   • Confirm that the battery is connected correctly to the BAT pin.
   • Check the ISET resistor value to ensure the charging current is set appropriately.
   • Verify the input voltage is sufficient for charging.

3. Overheating

   • Reduce the load on the BOOST or SYS pins.
   • Ensure adequate ventilation or add a heatsink if necessary.

4. I2C Communication Fails

   • Verify the SDA and SCL connections to the microcontroller.
   • Check the I2C address (default: 0x6B) and ensure no address conflicts.

Q: Can I use this IC with a 12V solar panel?
A: No, the input voltage range is limited to 3.5V to 6.5V. Use a step-down converter to reduce the voltage.

Q: What type of battery is supported?
A: The BQ25185 supports single-cell Li-Ion or Li-Polymer batteries.

Q: How do I configure the charging current?
A: Use an external resistor on the ISET pin. Refer to the datasheet for the resistor-to-current mapping.

Q: Can I power the system without a battery?
A: Yes, the SYS pin can provide power directly from the input source if no battery is connected.