Texas Instruments INA125U

Overview

INA125U from Texas Instruments (originally Burr-Brown) is a precision instrumentation amplifier with integrated voltage reference, designed for bridge sensor signal conditioning in industrial and battery-powered systems. It delivers 250 µV max input offset voltage, 100 dB min CMR at G=100, and selectable 2.5 V / 5 V / 10 V reference outputs - enabling direct excitation of strain gauge and RTD bridges.

For engineers reviewing the INA125U datasheet, INA125U pinout, INA125U application, or INA125U equivalent, this page provides verified technical context, gain-setting resistor guidance, sleep-mode timing behavior, reference accuracy vs temperature, and real-world single-supply bridge interface constraints - all specific to the SOIC-16 packaged INA125U variant.

Technical Context

The INA125U integrates two precision op amps (A1 and A2) in a three-op-amp instrumentation topology with laser-trimmed internal 60 kΩ gain-setting resistors. Its reference subsystem uses ratio-trimmed bandgap circuitry to deliver 1.24 V, 2.5 V, 5 V, or 10 V outputs with ±0.5% initial accuracy and ±35 ppm/°C drift.

Sleep mode is controlled by a logic-level input on Pin 2 (SLEEP), reducing quiescent current to ±1 µA typical when VSLEEP ≤ 100 mV. Wake-up time is 150 µs, and output impedance rises to ~80 kΩ during shutdown - requiring external buffering if driving low-impedance loads post-wake.

Key Specifications

Pinout & Package

INA125U is housed in a 16-pin SOIC (SO-16) surface-mount package with 1.27 mm pitch, JEDEC MS-012AC compliant, MSL Level-3 rated for reflow up to 260°C.

Key Features

Applications

Equivalent & Alternatives

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

Compared with INA125U, INA126UA saves 285 µA quiescent current but adds BOM cost and layout area for an external reference, while AD8226ARMZ improves noise by 13 nV/√Hz yet removes the key integration benefit of on-chip excitation - making INA125U optimal for compact, self-contained bridge amplifier designs.

Availability

INA125U is available at Aetrix Electronics and suitable for pressure transducer signal conditioning, multi-channel industrial data acquisition, and battery-powered portable instrumentation requiring stable component supply across extended temperature ranges.

Supply support for INA125U 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 and support for legacy precision analog products including the INA125 family.

The INA125 product line was engineered for high-accuracy sensor signal conditioning in harsh industrial environments, integrating precision amplification and stable excitation in a single SOIC package to reduce system size and calibration complexity.

FAQ

What is the maximum gain achievable with INA125U and how is it set?

The INA125U supports gains from 4 to 10,000 V/V, set by a single external resistor RG connected between Pins 7 and 8. The gain equation is G = 4 + 60 kΩ / RG. For G = 10,000, RG = 6.04 Ω is required - but trace resistance becomes significant, so use Kelvin connections and low-TCR resistors. The INA125U datasheet confirms this range applies to the SOIC-16 package under all specified supply conditions.

Can INA125U operate from a single 3.3 V supply, and what reference voltage options are available?

Yes, INA125U operates from +2.7 V to +36 V single supply. At +3.3 V, only the bandgap reference (1.24 V) is usable because V+ must exceed VREF by ≥1.25 V. Connecting VREFOUT to Pin 13 (VREFBG) yields 1.24 V ±0.5%, enabling ratiometric operation with 3.3 V ADCs. Higher references (2.5 V/5 V/10 V) require ≥3.75 V/6.25 V/11.25 V supplies respectively.

How does the SLEEP pin function on INA125U, and what happens to the reference output during shutdown?

The SLEEP pin (Pin 2) places INA125U into low-power mode when held ≤100 mV. Quiescent current drops to ±1 µA typical, and amplifier output impedance rises to ~80 kΩ. Critically, the voltage reference remains active and stable - VREFOUT continues delivering its selected voltage (e.g., 2.5 V) with full accuracy and low noise, allowing external circuits to remain powered during amplifier sleep.

What is the recommended layout practice for maintaining >100 dB CMR with INA125U?

To sustain >100 dB CMR, the IAREF pin (Pin 5) must be connected to a low-impedance ground plane with <12 Ω total resistance - including PCB trace, via, and connector resistance. Avoid routing noisy digital signals near IAREF or the VIN+/VIN– traces. Use symmetric 47 kΩ bias resistors from each input to IAREF for high-Z sources, and place 0.1 µF decoupling capacitors close to Pins 1 (V+) and 3 (V–) as shown in the INA125U datasheet Figure 1.

Does INA125U require external components for basic operation, and what are the minimum connections?

Yes, INA125U requires at minimum: (1) RG resistor between Pins 7 and 8 to set gain, (2) connection from VREFOUT (Pin 4) to one VREF pin (e.g., VREF5 for 5 V), and (3) 0.1 µF decoupling caps on V+ and V–. IAREF (Pin 5) must tie to system ground or sensor common. SLEEP (Pin 2) should connect to V+ if unused. No external compensation or trimming is needed - the INA125U is fully functional with these five connections.