How to Use AD627: Examples, Pinouts, and Specs

The AD627 is a low-cost, precision instrumentation amplifier designed for high accuracy and low noise applications. It is particularly well-suited for amplifying small differential signals in noisy environments due to its high common-mode rejection ratio (CMRR) and low offset voltage. The AD627 is compact, easy to use, and offers excellent performance, making it a popular choice for a wide range of applications.

• Medical instrumentation (e.g., ECG, EEG signal amplification)
• Sensor signal conditioning (e.g., strain gauges, thermocouples)
• Data acquisition systems
• Industrial process controls
• Portable instrumentation

• Supply Voltage Range: ±2.3 V to ±18 V (or 4.6 V to 36 V single supply)
• Input Offset Voltage: 50 µV (typical)
• Common-Mode Rejection Ratio (CMRR): 100 dB (minimum)
• Gain Range: 5 to 1000 (set by external resistor)
• Input Impedance: 10 GΩ (typical)
• Output Voltage Swing: Rail-to-rail
• Bandwidth: 80 kHz (at G = 5)
• Quiescent Current: 60 µA (typical)
• Package Options: 8-lead SOIC, 8-lead PDIP

The AD627 is available in an 8-pin package. The pinout and descriptions are as follows:

1. Power Supply: Connect the AD627 to a power supply within the range of ±2.3 V to ±18 V (dual supply) or 4.6 V to 36 V (single supply). Ensure proper decoupling capacitors (e.g., 0.1 µF and 10 µF) are placed close to the power pins.
2. Input Connections: Connect the differential signal to the +IN and -IN pins. Ensure the input signal is within the common-mode voltage range of the amplifier.
3. Gain Setting: Use an external resistor (RG) between the RG pins (pins 1 and 8) to set the desired gain. The gain is calculated as: [ G = 5 + \frac{200k\Omega}{R_G} ] If no resistor is connected, the default gain is 5.
4. Reference Voltage: Connect the REF pin to a reference voltage source (e.g., ground for single-supply operation) to set the output reference voltage.
5. Output Connection: The amplified signal is available at the OUT pin. Ensure the load impedance is appropriate for the application.

• Input Signal Range: Ensure the input signal does not exceed the common-mode voltage range to avoid distortion or clipping.
• Gain Resistor Selection: Use a precision resistor for RG to achieve accurate and stable gain.
• Decoupling Capacitors: Place decoupling capacitors close to the power supply pins to minimize noise and ensure stable operation.
• Output Loading: Avoid driving heavy loads directly from the output. Use a buffer if necessary.
• PCB Layout: Use a clean and low-noise PCB layout. Keep input traces short and away from noisy signals.

The AD627 can be used to amplify small sensor signals for an Arduino UNO. Below is an example of interfacing the AD627 with a thermocouple:

• Connect the thermocouple's differential output to the +IN and -IN pins of the AD627.
• Set the gain using an external resistor (e.g., 20 kΩ for a gain of 15).
• Connect the REF pin to ground.
• Connect the OUT pin to an analog input pin (e.g., A0) of the Arduino UNO.

// Example code to read amplified signal from AD627 using Arduino UNO

const int analogPin = A0; // Analog pin connected to AD627 OUT pin
float voltage = 0.0;      // Variable to store the measured voltage
float referenceVoltage = 5.0; // Arduino reference voltage (5V for default)

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

void loop() {
  int adcValue = analogRead(analogPin); // Read ADC value (0-1023)
  
  // Convert ADC value to voltage
  voltage = (adcValue / 1023.0) * referenceVoltage;
  
  // Print the measured voltage to the Serial Monitor
  Serial.print("Measured Voltage: ");
  Serial.print(voltage, 3); // Print voltage with 3 decimal places
  Serial.println(" V");
  
  delay(500); // Wait for 500 ms before the next reading
}

1. No Output Signal:

   • Verify the power supply connections and ensure the AD627 is powered correctly.
   • Check the input signal and ensure it is within the common-mode voltage range.
   • Confirm that the gain resistor (RG) is properly connected.

2. Output Clipping:

   • Ensure the input signal is not too large for the configured gain.
   • Verify that the REF pin is set to an appropriate reference voltage.

3. Excessive Noise:

   • Use proper decoupling capacitors on the power supply pins.
   • Ensure the input traces are short and shielded from noise sources.

4. Incorrect Gain:

   • Double-check the value of the external gain resistor (RG).
   • Ensure the resistor is a precision type with low tolerance.

Q: Can the AD627 operate with a single power supply?
A: Yes, the AD627 can operate with a single supply voltage ranging from 4.6 V to 36 V. Connect the -VS pin to ground in single-supply configurations.

Q: What is the maximum gain I can achieve with the AD627?
A: The maximum gain is 1000, which can be achieved by using an appropriate external resistor for RG.

Q: How do I minimize offset voltage errors?
A: Use precision resistors for gain setting and ensure the REF pin is connected to a stable reference voltage.

Q: Can I use the AD627 for AC signals?
A: Yes, the AD627 can amplify AC signals. However, ensure proper coupling capacitors are used if needed.