How to Use LM2956 Buck Converter DC-DC: Examples, Pinouts, and Specs

The LM2956 Buck Converter DC-DC is a highly efficient voltage step-down integrated circuit designed by ElectronicsComponents. It is commonly used in applications where a lower DC voltage is required from a higher DC voltage source. Typical use cases include battery-powered devices, power supplies, and embedded systems where power efficiency is crucial.

• Input Voltage (Vin): 4.5V to 28V
• Output Voltage (Vout): 1.23V to 20V (Adjustable)
• Output Current: Up to 3A (with proper heat sinking)
• Switching Frequency: 150 kHz
• Efficiency: Up to 92% (depends on input and output voltage, load current, and temperature)
• Operating Temperature: -40°C to +125°C

1. Input Supply: Connect a DC voltage source between the Vin and GND pins. Ensure that the source voltage is within the specified input range.
2. Output Voltage Setting: To set the desired output voltage, connect a resistor divider from Vout to Feedback to GND. The output voltage can be calculated using the formula: Vout = 1.23V * (1 + R1/R2), where R1 is connected between Vout and Feedback, and R2 is between Feedback and GND.
3. Load Connection: Connect your load to the Vout and GND pins.
4. ON/OFF Control (Optional): If you wish to control the output of the buck converter, connect a switch or logic signal to the ON/OFF pin.

• Heat Dissipation: Ensure adequate heat sinking for the LM2956 when drawing high currents, as power dissipation can lead to increased temperatures.
• Capacitor Selection: Use high-quality capacitors at the input and output for stability. Typically, low ESR capacitors are recommended.
• Inductor Selection: Choose an inductor that can handle the peak current without saturation and with minimal losses.
• PCB Layout: Keep the switch node (SW) trace short and away from sensitive analog areas to minimize noise and EMI.

• Output Voltage is Too High or Low: Check the resistor divider values and ensure they are within tolerance. Also, verify the feedback connection.
• Converter is Overheating: Ensure that the input voltage is within the specified range and that the load current does not exceed the maximum rating. Improve heat sinking or airflow if necessary.
• Output is Unstable: Verify the quality and placement of the input and output capacitors. Check the inductor for saturation or signs of damage.

• No Output Voltage: Ensure that the ON/OFF pin is set high if used. Check all connections and solder joints for continuity.
• Noise Issues: If noise is a concern, add a snubber circuit across the switch node or improve the PCB layout to minimize loop areas.

Q: Can I use the LM2956 without an external switch for the ON/OFF pin? A: Yes, the ON/OFF pin can be left floating or permanently connected to Vin if you do not require the enable/disable feature.

Q: What is the maximum output current of the LM2956? A: The LM2956 can deliver up to 3A of output current with proper heat sinking.

Q: How do I calculate the correct inductor value for my application? A: The inductor value depends on the input and output voltages, desired ripple current, and switching frequency. Use the datasheet guidelines and design tools provided by ElectronicsComponents for accurate selection.

// This example demonstrates how to control the LM2956 ON/OFF pin using an Arduino UNO.

const int onOffPin = 7; // Connect the ON/OFF pin of LM2956 to digital pin 7 on Arduino

void setup() {
  pinMode(onOffPin, OUTPUT); // Set the ON/OFF pin as an output
  digitalWrite(onOffPin, HIGH); // Enable the LM2956 output
}

void loop() {
  // The LM2956 output can be toggled on and off as needed
  digitalWrite(onOffPin, LOW); // Disable the LM2956 output
  delay(1000); // Wait for 1 second
  digitalWrite(onOffPin, HIGH); // Enable the LM2956 output
  delay(1000); // Wait for 1 second
}

Note: This code is for demonstration purposes only. Ensure that the rest of your circuit is correctly set up before connecting it to an Arduino.