How to Use INA125: Examples, Pinouts, and Specs

The INA125 is a low-power, precision instrumentation amplifier with a versatile precision voltage reference. It is designed to offer accurate signal amplification in measurement applications, featuring high common-mode rejection and low offset voltage. This makes the INA125 ideal for amplifying small differential signals in the presence of noise or common-mode signals. Common applications include industrial process controls, bridge amplifiers for pressure and strain gauges, and data acquisition systems.

• Supply Voltage (V(_{S})): 2.7V to 36V or ±1.35V to ±18V
• Input Bias Current (I(_{B})): 25nA maximum
• Input Offset Voltage (V(_{OS})): 250µV maximum
• Common-Mode Rejection Ratio (CMRR): 100dB minimum at G = 4
• Output Voltage Swing: 0.01V to V(_{S}) - 0.01V
• Operating Temperature Range: -40°C to +85°C

1. Power Supply: Connect the positive power supply to pin 7 (V({S})+) and the negative power supply to pin 5 (V({S})-). For single supply operation, ground pin 5.

2. Input Connections: Connect the positive side of the signal source to pin 3 (V({IN})+) and the negative side to pin 2 (V({IN})-).

3. Gain Setting: Place a precision resistor between pins 1 and 8 (RG) to set the desired gain. The gain can be calculated using the formula: G = 4 + (60kΩ / RG).

4. Output: The amplified signal can be taken from pin 6 (V(_{OUT})).

5. Reference Voltage (Optional): The reference pin (pin 4) can be used to set an output offset or to buffer the internal 2.5V reference voltage.

• Ensure that the power supply voltage does not exceed the recommended maximum to prevent damage to the INA125.
• Use precision resistors for setting the gain to achieve the desired accuracy.
• Keep the input signal within the specified common-mode voltage range to maintain linearity and common-mode rejection.
• Use bypass capacitors close to the power supply pins to minimize noise.
• Avoid running high-current traces or noisy signal lines near the INA125 to prevent interference.

• Output Not as Expected: Verify the gain setting resistor and input connections. Check the power supply levels and ensure that the INA125 is not in saturation.
• Excessive Noise: Ensure that the INA125 is properly decoupled with bypass capacitors. Keep the device away from noise sources and use shielded cables for the inputs if necessary.
• No Output: Check for proper power supply voltages and connections. Ensure that the input signal is within the specified range.

Q: Can the INA125 be used in a single-supply configuration? A: Yes, the INA125 can operate with a single supply by connecting the V(_{S})- pin to ground.

Q: What is the purpose of the reference pin on the INA125? A: The reference pin can be used to set an output offset voltage or to buffer the internal 2.5V reference voltage for external use.

Q: How do I set the gain of the INA125? A: The gain is set by connecting a resistor between pins 1 and 8. The gain formula is G = 4 + (60kΩ / RG).

Q: What should I do if the output is saturated at the supply rails? A: Check if the input signal is too large or if the gain is set too high. Adjust the gain or input signal accordingly.

// INA125 Example Code for Arduino UNO
// Connect the INA125 output to Arduino analog pin A0

const int ina125OutputPin = A0; // INA125 output connected to A0
int sensorValue = 0;            // Variable to store the sensor value

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

void loop() {
  sensorValue = analogRead(ina125OutputPin); // Read the analog value from INA125
  Serial.println(sensorValue);               // Print the value to the Serial Monitor
  delay(1000);                               // Wait for 1 second before the next read
}

Remember to adjust the gain and reference voltage according to your specific application needs. The above code is a simple starting point for reading the amplified signal from the INA125 using an Arduino UNO.