How to Use BQ25504: Examples, Pinouts, and Specs

The BQ25504 is a highly integrated energy harvesting management IC designed for ultra-low-power applications. It is specifically engineered to efficiently capture and manage energy from low-output sources such as solar cells, thermoelectric generators (TEGs), or piezoelectric devices. The BQ25504 is ideal for applications requiring energy harvesting to power small, energy-efficient devices while maximizing energy storage in supercapacitors or rechargeable batteries.

• Wireless sensor networks
• Internet of Things (IoT) devices
• Wearable electronics
• Remote monitoring systems
• Energy harvesting from solar panels or thermoelectric generators

1. Connect the Energy Source: Attach the energy harvesting source (e.g., solar panel or TEG) to the VIN_DC pin. Ensure the input voltage is within the specified range (80 mV to 3.6 V).
2. Configure MPPT: Use a resistor divider on the MPPT pin to set the Maximum Power Point Tracking (MPPT) ratio. This ensures the IC operates at the optimal power point of the energy source.
3. Connect the Storage Element: Attach a supercapacitor or rechargeable battery to the VSTOR pin. The IC will manage charging and discharging automatically.
4. Set Overvoltage Protection: Use a resistor divider on the VBAT_OV pin to set the overvoltage threshold for the storage element.
5. Load Connection: Connect the load to the VOUT pin. The IC will provide a regulated output voltage to power the load.
6. Enable Energy Harvesting: Ensure the EN_HRV pin is set high to enable energy harvesting functionality.

• Cold Start: The BQ25504 requires a minimum input voltage of 330 mV to cold start. Once started, it can operate with input voltages as low as 80 mV.
• MPPT Configuration: Properly configure the MPPT ratio to match the characteristics of your energy source for maximum efficiency.
• Storage Element Selection: Use a storage element with appropriate capacity and voltage ratings to ensure reliable operation.
• Thermal Management: Ensure adequate thermal dissipation if operating near the maximum power rating.

The BQ25504 can be used to power an Arduino UNO in low-power applications. Below is an example of how to monitor the VBAT_OK pin using the Arduino:

// Pin configuration
const int vbatOkPin = 2; // Connect VBAT_OK pin of BQ25504 to digital pin 2

void setup() {
  pinMode(vbatOkPin, INPUT); // Set VBAT_OK pin as input
  Serial.begin(9600);        // Initialize serial communication
}

void loop() {
  int vbatStatus = digitalRead(vbatOkPin); // Read VBAT_OK status

  if (vbatStatus == HIGH) {
    // VBAT_OK is HIGH, storage element voltage is within valid range
    Serial.println("Battery voltage is OK.");
  } else {
    // VBAT_OK is LOW, storage element voltage is outside valid range
    Serial.println("Battery voltage is NOT OK.");
  }

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

1. The IC does not start up:

   • Ensure the input voltage is at least 330 mV for cold start.
   • Check the connections to the VIN_DC pin and verify the energy source is functioning correctly.

2. Low efficiency in energy harvesting:

   • Verify the MPPT configuration. Adjust the resistor divider on the MPPT pin to match the energy source's characteristics.
   • Ensure the input voltage is within the specified range (80 mV to 3.6 V).

3. Storage element not charging:

   • Check the connections to the VSTOR pin and ensure the storage element is functional.
   • Verify the overvoltage threshold set on the VBAT_OV pin is appropriate for the storage element.

4. Output voltage is unstable:

   • Ensure the load connected to the VOUT pin does not exceed the IC's power capabilities.
   • Check for proper decoupling capacitors on the VOUT and VSTOR pins.

Q: Can the BQ25504 operate with input voltages below 330 mV?
A: The IC requires a minimum of 330 mV to cold start. Once started, it can operate with input voltages as low as 80 mV.

Q: What types of storage elements are compatible with the BQ25504?
A: The IC supports supercapacitors, Li-ion batteries, and other rechargeable storage elements within the specified voltage range.

Q: How do I configure the MPPT ratio?
A: Use a resistor divider on the MPPT pin to set the desired MPPT ratio. Refer to the datasheet for recommended resistor values based on your energy source.

Q: Can the BQ25504 power high-current loads?
A: The IC is designed for low-power applications. Ensure the load current does not exceed the IC's maximum output power rating.