Texas Instruments INA115BUG4

Overview

INA115BUG4 from Texas Instruments (originally Burr-Brown) is a precision instrumentation amplifier with 3-op-amp architecture, laser-trimmed for 50 µV max offset voltage, 0.25 µV/°C max drift, and 115 dB min CMRR at G=1000. It operates from ±2.25 V to ±18 V supplies and delivers ±13.5 V output swing into 2 kΩ at ±15 V - ideal for bridge sensor signal conditioning in industrial data acquisition systems.

For engineers reviewing the INA115BUG4 datasheet, INA115BUG4 pinout, INA115BUG4 application, or INA115BUG4 equivalent, this page provides verified technical context, gain-setting resistor guidance, over-voltage protection behavior, input bias current return path requirements, and validated alternatives for medical, RTD, thermocouple, and switched-gain amplifier designs.

Technical Context

The INA115BUG4 implements a three-op-amp topology with separate gain-sense terminals (pins 1 & 15), internal 25 kΩ feedback resistors, and independent over-voltage protection on each input (±40 V survivability). Its output amplifier (A3) drives loads up to 2 kΩ, while input amplifiers A1/A2 provide identical output swing but limited current drive (25 kΩ || 200 pF).

Gain is set by a single external resistor RG via G = 1 + 50 kΩ/RG, supporting 1–10,000× range. The 50 kΩ term derives from laser-trimmed on-chip metal film resistors, contributing directly to gain accuracy (±0.5% max at G=1000) and drift (±100 ppm/°C typical for the 50 kΩ network).

Key Specifications

Pinout & Package

SOL-16 surface-mount package (SOIC-16, DW package drawing), 16-pin wide-body outline with gull-wing leads, RoHS-compliant NiPdAu lead finish, MSL Level-3 (260°C peak reflow).

Key Features

Applications

Equivalent & Alternatives

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

Compared with INA115BUG4, INA128UA offers superior DC precision but lacks configurable gain-sense capability, while AD8421ARMZ delivers higher speed at the cost of robustness against ±40 V faults - making INA115BUG4 uniquely balanced for cost-sensitive, high-reliability industrial sensor front-ends.

Availability

INA115BUG4 is available at Aetrix Electronics and suitable for bridge amplifier, thermocouple amplifier, RTD sensor amplifier, switched-gain amplifier, and medical instrumentation requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for INA115BUG4 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 its precision analog portfolio, emphasizing high-accuracy signal conditioning for industrial, medical, and test equipment markets.

The INA115BUG4 belongs to TI's legacy instrumentation amplifier product line, designed specifically for low-cost, high-reliability sensor signal conditioning in environments demanding ±40 V fault tolerance and laser-trimmed DC performance.

FAQ

What is the correct way to connect the Ref pin on the INA115BUG4?

The Ref pin (pin 16) defines the output common-mode voltage and must be connected to a low-impedance node - ideally ground or a precision reference. A series resistance >5 Ω degrades CMRR to ~80 dB at G=1. For ratiometric systems, tie Ref to the same reference used by the downstream ADC. Always bypass Ref to local ground with a 0.1 µF ceramic capacitor. This ensures the INA115BUG4 maintains its specified 115 dB CMRR and prevents output offset drift.

How do I set gain to exactly 100 on the INA115BUG4?

To achieve G=100, use RG = 505.1 Ω per the gain equation G = 1 + 50 kΩ/RG. The nearest 1% standard value is 511 Ω, yielding G ≈ 98.9 - within the ±0.7% gain error spec at G=100. For tighter accuracy, select a 0.1% resistor (e.g., 505 Ω) and verify with bench measurement. Note that RG contributes directly to gain drift; use a low-TCR (≤25 ppm/°C) metal film resistor to maintain stability across temperature. The INA115BUG4's internal 50 kΩ network is laser-trimmed, so external RG dominates total error.

Does the INA115BUG4 require external input protection when used with ±15 V supplies?

No - the INA115BUG4 includes integrated ±40 V input protection on both IN+ and IN– pins, fully functional even with supplies at 0 V. This eliminates the need for external clamping diodes or series resistors in most industrial applications. However, if inputs may experience repetitive >±40 V transients (e.g., lightning-induced surges), add external TVS diodes rated for >±45 V standoff. The internal protection limits input current to ~1.5 mA during overload, preserving device integrity without latch-up. Always verify protection adequacy per IEC 61000-4-5 requirements for your end equipment.

Can the INA115BUG4 operate from a single +5 V supply?

Yes - the INA115BUG4 supports single-supply operation with V+ = +5 V and V– = 0 V (ground), meeting its ±2.25 V minimum supply requirement. Output swing is reduced: ±1.5 V typical into 2 kΩ at +5 V. To maximize dynamic range, bias the Ref pin at V+/2 (2.5 V) using a resistor divider or precision buffer. Input common-mode range becomes 0.25 V to 4.75 V. Confirm that sensor output stays within this window. The INA115BUG4's rail-to-rail output stage is not included - output saturates ~1.5 V from each rail - so design accordingly for headroom.

What is the purpose of pins 1 (VO1) and 10 (VO2) on the INA115BUG4?

Pins 1 (VO1) and 10 (VO2) are the outputs of the two input-stage operational amplifiers (A1 and A2). They are not intended as primary outputs but serve as gain-sense points for precision feedback. In standard configuration, VO1 connects to pin 2 (Gain Sense1) and VO2 to pin 14 (Gain Sense2) to close the A1/A2 loops. These pins enable advanced topologies: remote-sense feedback to reduce PCB trace errors, or switched-gain circuits using multiplexers on RG paths. Misconnecting them causes gain inaccuracy or instability. Never load VO1/VO2 directly - they drive only high-impedance feedback nodes.