How to Use LM4140 High Precision Low Noise Low Dropout Voltage Reference: Examples, Pinouts, and Specs

The LM4140 is a high-precision, low-noise, low-dropout voltage reference manufactured by Texas Instruments. It is designed to provide a stable and accurate output voltage, making it ideal for precision applications such as data acquisition systems, instrumentation, and high-resolution analog-to-digital converters (ADCs). The LM4140 is known for its exceptional temperature stability, low noise performance, and low power consumption.

• High-resolution ADCs and DACs
• Precision measurement systems
• Test and measurement equipment
• Medical instrumentation
• Industrial process control
• Calibration equipment

The LM4140 is available in multiple output voltage options, including 2.5V, 4.096V, and 5.0V. Below are the key technical details:

The LM4140 is commonly available in an 8-pin SOIC package. Below is the pinout and description:

Note: Pins labeled "NC" should not be connected to any circuit.

1. Power Supply: Connect the input voltage (VIN) to a stable power source within the range of 2.7V to 5.5V. Ensure the power supply is free of significant noise or fluctuations.
2. Ground Connection: Connect the GND pin to the ground of your circuit.
3. Output Voltage: The VOUT pin provides the stable reference voltage. Connect this pin to the load or circuit requiring the reference voltage.
4. Bypass Capacitors: Place a 0.1 µF ceramic capacitor close to the VIN pin to filter high-frequency noise. Additionally, a 1 µF capacitor can be placed at the VOUT pin to improve stability and transient response.

• Thermal Management: Ensure the LM4140 operates within its specified temperature range (-40°C to +125°C). Use proper heat dissipation techniques if necessary.
• Load Current: Avoid exceeding the maximum load current to maintain output voltage accuracy.
• PCB Layout: Minimize noise and interference by using a clean ground plane and keeping traces to the VOUT pin short and direct.
• Startup Time: Allow sufficient time for the LM4140 to stabilize after power-up before using the output voltage.

The LM4140 can be used as a precision reference voltage for an Arduino UNO's ADC. Below is an example of how to connect and use it:

1. Connect the LM4140's VIN pin to the Arduino's 5V pin.
2. Connect the GND pin to the Arduino's GND.
3. Connect the VOUT pin to the Arduino's AREF pin (Analog Reference).

// Example: Using LM4140 as an external reference for Arduino ADC
// Connect LM4140 VOUT to AREF pin, and set the ADC reference to EXTERNAL.

void setup() {
  // Set the ADC reference to external (using LM4140)
  analogReference(EXTERNAL);

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

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

  // Convert the ADC value to voltage (assuming 4.096V reference)
  float voltage = sensorValue * (4.096 / 1023.0);

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

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

Note: Replace 4.096 in the code with the actual output voltage of your LM4140 (e.g., 2.5 or 5.0) if using a different variant.

1. Output Voltage is Incorrect or Unstable

   • Cause: Insufficient bypass capacitors or noisy power supply.
   • Solution: Add a 0.1 µF capacitor near the VIN pin and a 1 µF capacitor near the VOUT pin.

2. Device Overheating

   • Cause: Excessive load current or high ambient temperature.
   • Solution: Reduce the load current or improve thermal dissipation.

3. No Output Voltage

   • Cause: Incorrect wiring or insufficient input voltage.
   • Solution: Verify all connections and ensure the input voltage is within the specified range.

4. ADC Readings are Inaccurate (with Arduino)

   • Cause: Incorrect reference voltage setting in the Arduino code.
   • Solution: Ensure analogReference(EXTERNAL) is used in the code and the LM4140's VOUT is connected to the AREF pin.

Q: Can the LM4140 be used with a 3.3V power supply?
A: Yes, the LM4140 can operate with input voltages as low as 2.7V. Ensure the output voltage variant you select is compatible with your application.

Q: What is the maximum load current the LM4140 can drive?
A: The LM4140 is designed for low-current applications and can typically drive up to 10 mA.

Q: Can I use the LM4140 without bypass capacitors?
A: While the LM4140 can function without bypass capacitors, it is highly recommended to use them to ensure stability and minimize noise.

Q: Is the LM4140 suitable for battery-powered applications?
A: Yes, the LM4140's low quiescent current (1 mA typical) makes it suitable for battery-powered systems.