How to Use ina149: Examples, Pinouts, and Specs

The INA149 is a precision instrumentation amplifier designed for low-power applications. It features high input impedance, low offset voltage, and low noise, making it ideal for amplifying small differential signals in the presence of large common-mode voltages. This component is particularly suited for applications requiring accurate signal amplification in environments with high common-mode voltages, such as industrial process controls, medical instrumentation, and data acquisition systems.

• Industrial process control systems
• Medical instrumentation
• Data acquisition systems
• High-voltage signal monitoring
• Precision measurement systems

• Supply Voltage Range: ±2.25V to ±18V (dual supply) or 4.5V to 36V (single supply)
• Input Impedance: 10 GΩ (typical)
• Common-Mode Voltage Range: ±275V
• Gain: Fixed at 1
• Offset Voltage: ±0.5 mV (maximum)
• Input Bias Current: ±25 nA (typical)
• Bandwidth: 500 kHz (typical)
• Slew Rate: 1 V/μs
• Operating Temperature Range: -40°C to +85°C
• Package Options: SOIC-8, PDIP-8

The INA149 is available in an 8-pin package. The pinout and descriptions are as follows:

1. Power Supply: Connect the INA149 to a power supply within the specified range. For dual-supply operation, connect V+ to the positive voltage and V- to the negative voltage. For single-supply operation, connect V+ to the positive voltage and V- to ground.
2. Input Connections: Connect the differential signal to the +IN and -IN pins. Ensure the common-mode voltage is within the specified range (±275V).
3. Reference Voltage: Use the REF pin to set the output reference voltage. For example, connect it to ground for a ground-referenced output or to a voltage divider for a custom reference.
4. Output: The amplified differential signal will be available at the OUT pin. Connect this pin to the next stage of your circuit (e.g., an ADC or microcontroller input).

• Bypass Capacitors: Place decoupling capacitors (e.g., 0.1 μF and 10 μF) close to the power supply pins (V+ and V-) to reduce noise and improve stability.
• Input Protection: If the input signal may exceed the common-mode voltage range, use external resistors or diodes to protect the inputs.
• PCB Layout: Use a clean and low-noise PCB layout. Keep input traces short and away from noisy signals to minimize interference.
• Reference Voltage: Ensure the REF pin is properly connected to avoid unexpected output behavior.

The INA149 can be used to amplify a differential signal for an Arduino UNO's ADC input. Below is an example circuit and code:

• Connect +IN and -IN to the differential signal source.
• Connect REF to ground for a ground-referenced output.
• Connect OUT to an analog input pin (e.g., A0) on the Arduino UNO.
• Power the INA149 with a 5V single supply (V+ to 5V, V- to ground).

// INA149 Example Code for Arduino UNO
// Reads the amplified differential signal from the INA149 and prints the value

const int analogPin = A0; // Analog pin connected to INA149 OUT pin

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

void loop() {
  int adcValue = analogRead(analogPin); // Read the ADC value (0-1023)
  
  // Convert ADC value to voltage (assuming 5V reference for Arduino ADC)
  float voltage = (adcValue / 1023.0) * 5.0;
  
  // Print the voltage to the serial monitor
  Serial.print("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 that the power supply is connected and within the specified range.
   • Check the input connections to ensure the differential signal is properly applied.
   • Ensure the REF pin is connected to a valid reference voltage.

2. Output Saturation:

   • Confirm that the input common-mode voltage is within the specified range (±275V).
   • Check if the output load is too high; the INA149 is designed for high-impedance loads.

3. High Noise in Output:

   • Add bypass capacitors close to the power supply pins to reduce noise.
   • Ensure the input traces are short and shielded from noisy signals.

4. Incorrect Output Voltage:

   • Verify the REF pin voltage. An incorrect reference voltage can shift the output.
   • Check for any wiring errors or loose connections.

Q: Can the INA149 amplify signals with a common-mode voltage higher than the supply voltage?
A: Yes, the INA149 can handle common-mode voltages up to ±275V, even if the supply voltage is much lower. This is one of its key features.

Q: What is the maximum output current of the INA149?
A: The INA149 can source or sink up to 10 mA. Ensure the load impedance is high enough to avoid overloading the output.

Q: Can I use the INA149 with a single power supply?
A: Yes, the INA149 supports single-supply operation. Connect V+ to the positive supply voltage and V- to ground.

Q: How do I set the gain of the INA149?
A: The INA149 has a fixed gain of 1 and does not support external gain adjustment. If additional gain is required, use an external amplifier stage.