How to Use LM2621: Examples, Pinouts, and Specs

The LM2621 is a high-efficiency, step-down (buck) voltage regulator capable of delivering up to 1A of output current. It operates over a wide input voltage range of 2V to 14V, making it versatile for various power supply applications. With its low quiescent current, the LM2621 is particularly well-suited for battery-powered devices, where energy efficiency is critical. Additionally, the device includes built-in protection features such as thermal shutdown and current limiting, ensuring reliable operation under demanding conditions.

• Portable and battery-powered devices
• Point-of-load power supplies
• Industrial and automotive electronics
• Consumer electronics (e.g., smartphones, tablets, and wearables)

The LM2621 is typically available in an 8-pin SOIC or MSOP package. Below is the pinout and description:

1. Input and Output Capacitors:

   • Place a low-ESR ceramic capacitor (e.g., 10µF) close to the VIN pin to filter input noise.
   • Use a similar capacitor (e.g., 22µF) at the output to stabilize the voltage and reduce ripple.

2. Inductor Selection:

   • Choose an inductor with a current rating higher than the maximum output current (1A).
   • The inductance value typically ranges from 4.7µH to 22µH, depending on the desired ripple current.

3. Feedback Resistor Divider:

   • Use two resistors to set the output voltage. The formula is: [ V_{OUT} = V_{REF} \times \left(1 + \frac{R1}{R2}\right) ] where ( V_{REF} ) is 0.8V (internal reference voltage).

4. Compensation:

   • Connect a capacitor (e.g., 1nF to 10nF) to the COMP pin to stabilize the control loop.

5. Enable/Disable:

   • Pull the SHDN pin high (above 1.6V) to enable the regulator.
   • Pull it low (below 0.4V) to disable the regulator and reduce power consumption.

The LM2621 can be used to power an Arduino UNO from a higher voltage source (e.g., a 12V battery). Below is an example circuit and Arduino code to monitor the output voltage.

• Connect the LM2621 as follows:
  • VIN: 12V battery
  • VOUT: 5V (set using the feedback resistor divider)
  • GND: Common ground
  • SHDN: Connected to a digital pin on the Arduino for control

// LM2621 Output Voltage Monitoring and Control
const int shdnPin = 7;  // Pin connected to SHDN pin of LM2621
const int voutPin = A0; // Analog pin to read output voltage

void setup() {
  pinMode(shdnPin, OUTPUT); // Set SHDN pin as output
  digitalWrite(shdnPin, HIGH); // Enable the LM2621 regulator

  Serial.begin(9600); // Initialize serial communication
}

void loop() {
  // Read the output voltage (scaled by a resistor divider)
  int analogValue = analogRead(voutPin);
  
  // Convert the analog reading to voltage (assuming 10-bit ADC and 5V reference)
  float outputVoltage = (analogValue / 1023.0) * 5.0 * 2; 
  // Multiply by 2 if a 1:1 resistor divider is used

  // Print the output voltage to the serial monitor
  Serial.print("Output Voltage: ");
  Serial.print(outputVoltage);
  Serial.println(" V");

  delay(1000); // Wait for 1 second before the next reading
}

• Thermal Management: Ensure adequate heat dissipation, especially at high currents. Use a PCB with good thermal conductivity or add a heatsink if necessary.
• Input Voltage Range: Do not exceed the maximum input voltage of 14V to avoid damaging the device.
• Output Ripple: Minimize output ripple by using low-ESR capacitors and proper PCB layout techniques.

1. No Output Voltage:

   • Check if the SHDN pin is pulled high to enable the regulator.
   • Verify the input voltage is within the specified range (2V to 14V).
   • Inspect the feedback resistor divider for correct values.

2. Excessive Output Ripple:

   • Use low-ESR capacitors at the input and output.
   • Ensure the inductor value is appropriate for the desired ripple current.

3. Overheating:

   • Verify that the load current does not exceed 1A.
   • Improve thermal dissipation by using a larger PCB area for the GND plane.

4. Device Not Switching:

   • Check the COMP pin capacitor for proper value and connection.
   • Ensure the switching frequency is set correctly (if adjustable).

Q: Can the LM2621 be used for negative output voltages?
A: No, the LM2621 is designed for step-down (buck) operation and cannot generate negative voltages.

Q: What happens if the input voltage drops below 2V?
A: The regulator will stop operating, and the output voltage will drop. Ensure the input voltage remains within the specified range.

Q: Can I use the LM2621 for applications requiring more than 1A?
A: No, the LM2621 is rated for a maximum output current of 1A. For higher currents, consider using a different regulator with a higher current rating.

Q: How do I calculate the efficiency of the LM2621?
A: Efficiency can be calculated as: [ \text{Efficiency} = \left(\frac{V_{OUT} \times I_{OUT}}{V_{IN} \times I_{IN}}\right) \times 100% ] Measure ( V_{IN} ), ( V_{OUT} ), ( I_{IN} ), and ( I_{OUT} ) to determine efficiency.

This concludes the LM2621 documentation.