Texas Instruments INA115AU

Overview

INA115AU from Texas Instruments (originally Burr-Brown) is a precision instrumentation amplifier with three-op-amp architecture, designed for high-accuracy signal conditioning in low-noise, high-common-mode-noise environments. It delivers 115dB min CMRR at G=1000, ±40V input over-voltage protection, and 50µV max initial offset voltage - enabling use in bridge sensor interfaces, thermocouple amplification, and medical ECG front-ends.

For engineers reviewing the INA115AU datasheet, INA115AU pinout, INA115AU application, or INA115AU equivalent, key selection considerations include its SOL-16 (SOIC-16) package, gain-setting via single external resistor (G = 1 + 50kΩ/R_G), ±2.25V to ±18V dual-supply operation, and –40°C to +85°C industrial temperature range.

Technical Context

The INA115AU implements a classic three-op-amp topology with independently accessible input op-amp outputs (VO1, VO2) and dedicated feedback (pin 12) and reference (Ref, pin 7) terminals - enabling switched-gain configurations, remote-sense accuracy, and precise common-mode rejection control. Its laser-trimmed 25kΩ internal feedback resistors and on-chip over-voltage protection circuitry (±40V survivable) define its robustness in noisy industrial transducer interfaces.

Unlike monolithic single-amplifier architectures, the INA115AU's modular design allows external gain-setting resistor RG to directly set gain from 1 to 10,000 while maintaining low drift (0.25µV/°C max) and high DC accuracy - critical for RTD and strain gauge measurements where long-term stability and thermal matching dominate error budgets.

Key Specifications

Pinout & Package

SOL-16 surface-mount package (SOIC-16, TI package code DW), 16-pin wide-body outline with standard 1.27 mm pitch; specified for –40°C to +85°C ambient operation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar instrumentation amplifier applications.

Compared with INA125P and AD620ARZ, the INA115AU offers superior CMRR (115 dB vs ≤100 dB) and lower offset (50 µV vs ≥125 µV), making it optimal for high-precision bridge and thermocouple applications where common-mode noise immunity and DC accuracy are non-negotiable.

Availability

INA115AU is available at Aetrix Electronics and suitable for industrial sensor interfaces, medical diagnostics equipment, and test & measurement instrumentation requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for INA115AU includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments acquired Burr-Brown in 2000 and maintains full production, qualification, and technical support for legacy precision analog products including the INA115 series.

The INA115 product line was engineered for high-accuracy, low-drift signal conditioning in industrial, medical, and scientific instrumentation - emphasizing laser-trimmed DC performance, robust input protection, and flexible gain architecture over speed or integration density.

FAQ

What is the maximum safe input voltage for the INA115AU?

The INA115AU features integrated input over-voltage protection rated for ±40V - meaning either input (VIN+ or VIN–) can withstand up to +40V or –40V relative to ground without damage, even with power supplies off. This specification is absolute maximum and applies regardless of gain setting or supply voltage; sustained operation above ±13.5V common-mode requires verification against the Input Common-Mode Range vs Output Voltage curve in the INA115AU datasheet.

How do I configure the INA115AU for G = 1 operation?

To configure the INA115AU for unity gain, leave RG (pin 6) unconnected and short pins 2–3 (VIN– to VIN+) and pins 14–15 (Gain Sense2 to VO2). For reduced gain peaking, also short pins 1–2–3 and pins 8–14–15 to bypass internal 25kΩ feedback resistors. The INA115AU achieves true G = 1 with no external resistor, leveraging its internal 50kΩ trimmed network per the gain equation G = 1 + 50kΩ/RG.

Does the INA115AU require external decoupling capacitors?

Yes - the INA115AU requires 0.1 µF ceramic decoupling capacitors placed as close as possible to pins 4 (V–) and 5 (V+), referenced to a low-impedance ground plane. These capacitors suppress high-frequency supply noise and prevent oscillation, especially in noisy industrial environments or when driving reactive loads. Failure to install them may cause instability, increased output noise, or degraded CMRR in the INA115AU.

Can the INA115AU operate from a single 5V supply?

Yes - the INA115AU supports single-supply operation down to +5V (±2.5V equivalent) with appropriate level-shifting of the Ref (pin 7) node to mid-supply (e.g., 2.5V). Output swing is limited to approximately ±1.5V under ±2.25V supplies, so for 5V systems, biasing Ref to 2.5V enables rail-to-rail output centered at 2.5V. The INA115AU's quiescent current remains ≤3 mA, making it viable for battery-powered instrumentation.

What is the purpose of the Feedback (pin 12) and Ref (pin 7) terminals on the INA115AU?

The Feedback (pin 12) terminal provides access to the output-stage feedback node and must be connected to VO (pin 11) for standard operation; it enables remote sensing at the load for improved accuracy. The Ref (pin 7) terminal sets the output common-mode voltage - typically grounded - and must be held at low impedance (<5 Ω) to maintain specified CMRR; any series resistance here degrades rejection by up to 35 dB per ohm in the INA115AU.