Texas Instruments INA111BU

Overview

INA111BU from Texas Instruments (formerly Burr-Brown) is a high-speed, FET-input instrumentation amplifier optimized for precision DC-coupled signal conditioning in data acquisition and medical instrumentation. It delivers 4µs settling time to 0.01% at G=100, 106dB minimum CMRR at G=100, ±500µV max input offset voltage, and operates from ±6V to ±18V supplies across –40°C to +85°C.

For engineers reviewing the INA111BU datasheet, INA111BU pinout, INA111BU application, or INA111BU equivalent, key selection considerations include its current-feedback topology enabling 2MHz bandwidth at G=1, laser-trimmed DC accuracy, 16-pin SOIC package with dedicated output sense pin (Pin 12), and FET-input bias current <20pA for high-impedance sensor interfacing.

Technical Context

The INA111BU employs a three-op-amp current-feedback architecture with internal 50kΩ trimmed feedback resistors, enabling gain setting via a single external resistor RG (G = 1 + 50kΩ/RG). Its differential input stage uses matched FETs to achieve ultra-low input bias current and high common-mode rejection.

Unlike voltage-feedback amplifiers, the INA111BU exhibits a predictable +6dB/octave gain rise near 2MHz due to a response zero-this is inherent to its topology and does not indicate instability. The SOL-16 package includes a dedicated output sense terminal (Pin 12) for remote load sensing, internally connected in the DIP variant.

Key Specifications

Pinout & Package

INA111BU is housed in a 16-pin SOIC (DW) surface-mount package per JEDEC MS-013, with 1.27mm pitch and moisture sensitivity level 3 (260°C reflow).

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD8421ARZ and INA826AIDR, the INA111BU uniquely balances high speed (4µs settling), FET-input integrity (<20pA), and integrated output sensing-making it optimal for industrial DAQ channels where load regulation and moderate power consumption are prioritized over ultra-low bias or rail-to-rail swing.

Availability

INA111BU is available at Aetrix Electronics and suitable for medical instrumentation, industrial data acquisition, and precision sensor signal conditioning requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for INA111BU 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, renowned for high-performance op amps, data converters, and interface ICs used in test equipment, medical systems, and industrial automation.

The INA111BU belongs to TI's legacy instrumentation amplifier family designed specifically for high-fidelity, DC-coupled sensor signal conditioning-emphasizing laser-trimmed accuracy, FET-input integrity, and robustness in noisy, real-world measurement environments.

FAQ

What is the function of Pin 12 (Feedback) on the INA111BU?

Pin 12 is the dedicated output sense terminal for Kelvin feedback. It must be connected to Pin 11 (VO) for standard operation. When driving remote loads, connecting Pin 12 directly to the load return point compensates for voltage drop across interconnects, preserving closed-loop accuracy. This feature is exclusive to the SOIC package; the DIP version connects this internally.

Can the INA111BU operate with a single supply?

No, the INA111BU requires dual symmetric supplies (±6V to ±18V) as specified in its absolute maximum ratings and electrical characteristics. Its input common-mode range extends only to (V–) –0.7V and (V+) +15V, and output swing is centered around ground. Single-supply operation would violate input/output voltage limits and cause saturation.

How does the INA111BU's current-feedback architecture affect stability with capacitive loads?

The INA111BU's current-feedback topology provides inherent stability with capacitive loads up to 1000pF, as stated in its specifications. Unlike voltage-feedback amplifiers, it does not require external isolation resistors for typical PCB trace capacitance. However, loads >1000pF may require a small series resistor (10–50Ω) at the output to dampen peaking.

What is the recommended layout practice for maintaining >100dB CMRR with the INA111BU?

To achieve >100dB CMRR, route VIN+ and VIN– traces as a tightly coupled differential pair with identical length and impedance, place a solid ground plane beneath them, and keep the Ref pin connection to ground shorter than 5mm with <2Ω impedance. Avoid routing digital or switching signals near these traces, and use matched 1% resistors if external gain-setting networks are employed.

Does the INA111BU require external offset trimming in most applications?

No, the INA111BU is laser-trimmed for low offset voltage (±500µV max) and drift (5µV/°C max), making external trimming unnecessary in typical applications. Figure 2 in the datasheet shows an optional circuit using an OPA177 op amp only for cases demanding sub-100µV residual offset-such as high-gain thermopile amplification where even small offsets dominate error budgets.