How to Use LM4128-2.5VREF: Examples, Pinouts, and Specs

The LM4128-2.5VREF is a precision voltage reference designed to provide a stable and accurate output voltage of 2.5V. It is characterized by its low output noise, low temperature coefficient, and excellent long-term stability. These features make it an ideal choice for precision analog circuits, as well as for use as a reference voltage in Analog-to-Digital Converters (ADCs) and Digital-to-Analog Converters (DACs).

• Precision measurement systems
• Data acquisition systems
• Voltage references for ADCs and DACs
• Portable and battery-powered devices
• Industrial control systems

The LM4128-2.5VREF is available in a 5-pin SOT-23 package. The pinout is as follows:

1. Power Supply: Connect the VIN pin to a stable power supply within the range of 2.7V to 5.5V. Ensure the supply voltage is free from excessive noise or fluctuations.
2. Output Voltage: Connect the VOUT pin to the circuit requiring a 2.5V reference. Use a decoupling capacitor (e.g., 0.1 µF ceramic) close to the VOUT pin to minimize noise.
3. Ground Connection: Connect the GND pin to the ground plane of your circuit.
4. Shutdown Pin (Optional): If you wish to enable or disable the voltage reference, connect the SHDN pin to a control signal. Pulling SHDN low disables the output, while pulling it high (or leaving it unconnected) enables the output.

• Decoupling Capacitors: Place a 0.1 µF ceramic capacitor close to the VIN pin to filter supply noise. Similarly, place a capacitor near the VOUT pin for stability and noise reduction.
• Thermal Management: Ensure the device operates within its specified temperature range (-40°C to +125°C). Avoid placing the component near heat sources.
• Load Current: Do not exceed the maximum output current of ±5 mA to maintain accuracy and stability.
• PCB Layout: Use a low-impedance ground plane and minimize trace lengths to reduce noise and improve performance.

The LM4128-2.5VREF can be used as a reference voltage for the Arduino UNO's ADC. Below is an example of how to connect and use it:

• Connect the LM4128's VOUT pin to the AREF pin of the Arduino UNO.
• Connect the GND pin of the LM4128 to the Arduino's GND.
• Connect the VIN pin of the LM4128 to the Arduino's 5V pin.

// Example code to use LM4128-2.5VREF as an external reference for Arduino ADC

void setup() {
  // Set the ADC reference to external (using LM4128's 2.5V output)
  analogReference(EXTERNAL);

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

void loop() {
  // Read analog input from pin A0
  int sensorValue = analogRead(A0);

  // Convert the ADC value to voltage (2.5V reference, 10-bit ADC)
  float voltage = sensorValue * (2.5 / 1023.0);

  // Print the voltage to the Serial Monitor
  Serial.print("Voltage: ");
  Serial.print(voltage);
  Serial.println(" V");

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

1. No Output Voltage:

   • Ensure the VIN pin is connected to a stable power supply within the specified range (2.7V to 5.5V).
   • Verify that the SHDN pin is not pulled low. If unused, leave it unconnected or pull it high.

2. Output Voltage is Incorrect:

   • Check for excessive load current. The LM4128 can only source or sink up to ±5 mA.
   • Verify the decoupling capacitors are properly placed and of the correct value.

3. High Noise on Output:

   • Ensure a 0.1 µF ceramic capacitor is placed close to the VOUT pin.
   • Minimize noise on the VIN pin by using a clean power supply and proper decoupling.

4. Device Overheating:

   • Check for excessive input voltage or load current.
   • Ensure proper thermal management and avoid placing the device near heat sources.

Q1: Can I use the LM4128-2.5VREF with a 3.3V power supply?
A1: Yes, the LM4128 operates with input voltages as low as 2.7V, so it is compatible with a 3.3V supply.

Q2: What happens if the SHDN pin is left floating?
A2: The SHDN pin has an internal pull-up resistor, so leaving it floating will enable the device by default.

Q3: Can the LM4128-2.5VREF drive multiple loads?
A3: Yes, as long as the total load current does not exceed ±5 mA and the loads are properly decoupled.

Q4: Is the LM4128-2.5VREF suitable for battery-powered applications?
A4: Yes, its low quiescent current (160 µA typical) makes it ideal for low-power applications.