Texas Instruments INA118U

Overview

INA118U from Texas Instruments is a precision, low-power instrumentation amplifier designed for high-accuracy signal conditioning of low-level differential signals in the presence of large common-mode voltages. It delivers 50 µV max offset voltage, 0.5 µV/°C max drift, 110 dB min CMR at G = 1000, ±2.25 V to ±18 V supply range, and 350 µA quiescent current - enabling use in battery-powered ECG monitors and industrial pressure transmitters.

For engineers reviewing the INA118U datasheet, INA118U pinout, INA118U application, or INA118U equivalent, key selection considerations include its laser-trimmed gain-setting architecture (G = 1 + 50 kΩ/R_G), ±40 V input overvoltage protection, SOIC-8 package compatibility, and trade-offs versus newer alternatives like the INA818 in offset and noise performance.

Technical Context

The INA118U employs a three-op-amp topology with JFET-input stages and current-feedback architecture, delivering 70 kHz bandwidth at G = 100 and 800 kHz at G = 1. Its input stage uses dual FETs per input to provide ±40 V fault tolerance while maintaining low series impedance during normal operation.

Gain is set externally via a single resistor (RG) between pins 1 and 8, leveraging laser-trimmed 25 kΩ internal resistors. The output amplifier references the Ref pin, requiring low-impedance connection to preserve CMR - a 12 Ω series resistance degrades CMR to ~80 dB at G = 1.

Key Specifications

Pinout & Package

INA118U is available in an 8-pin SOIC (SO-8) package measuring 3.91 mm × 4.90 mm, rated for –40°C to +125°C operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with INA118U, the INA818 offers superior DC precision and noise for high-end test equipment, while the INA333 provides chopper-stabilized zero-drift performance and ultra-low supply voltage support - making each suitable for distinct segments of precision analog signal chains where trade-offs among offset, noise, supply, and cost are prioritized.

Availability

INA118U is available at Aetrix Electronics and suitable for pressure transmitters, ECG monitors, weigh scales, and industrial analog input modules requiring stable component supply across extended product lifecycles.

Supply support for INA118U 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 is a global semiconductor leader specializing in analog and embedded processing technologies, with decades of leadership in precision amplifier design.

The INA118U belongs to TI's precision instrumentation amplifier product line, engineered specifically for high-accuracy, low-power signal conditioning in industrial sensing, medical instrumentation, and data acquisition systems.

FAQ

What is the maximum gain achievable with the INA118U?

The INA118U supports gains from 1 to 10000, set by an external resistor RG using the equation G = 1 + 50 kΩ / RG. For G = 10000, RG = 5 Ω is required - but practical implementation must account for PCB trace resistance and resistor tolerance, especially above G = 100 where wiring resistance contributes measurable error. The INA118U datasheet confirms this range under recommended operating conditions.

Does the INA118U require external components for basic operation?

Yes - the INA118U requires an external gain-setting resistor (RG) between pins 1 and 8 to configure gain. Additionally, local 0.1 µF decoupling capacitors on V+ and V– pins are recommended for stable operation in noisy environments. The Ref pin must be driven by a low-impedance source (e.g., grounded or buffered voltage) to maintain specified CMR; a 12 Ω series resistance degrades CMR to ~80 dB at G = 1.

What is the input overvoltage protection capability of the INA118U?

The INA118U inputs are protected to ±40 V - meaning each input can withstand up to +40 V or –40 V relative to ground, even with power supplies disconnected. This protection is implemented via integrated JFETs that limit input current to approximately 6 mA during overload. The device remains undamaged under conditions such as –40 V on one input and +40 V on the other, eliminating need for external clamping in most industrial field applications.

How does the INA118U perform in single-supply configurations?

The INA118U operates with single supplies down to 4.5 V (V+ = 4.5 V, V– = 0 V), delivering output swing from 60 mV to 2 V (typical). Input common-mode range is reduced in single-supply mode - e.g., at V+ = 4.5 V, linear input range is approximately 0.2 V to 2.8 V. Figure 7-5 and 7-6 in the INA118U datasheet detail this behavior. Proper Ref pin biasing (e.g., to V+/2) is essential to maximize dynamic range in single-supply use cases like portable sensors.

Is the INA118U pin-compatible with the INA818?

No - the INA118U and INA818 are not pin-compatible. While both use 8-pin SOIC packages and share the same RG gain-setting architecture (G = 1 + 50 kΩ / RG), the INA818 places RG pins at 1 and 8, whereas the INA118U also uses pins 1 and 8 for RG. However, internal architecture differences, updated ESD structures, and revised thermal characteristics mean direct PCB replacement is not supported without validation. TI's Device Comparison Table explicitly lists them as functionally similar but not drop-in replacements.