Texas Instruments INA121U/2K5G4

Overview

INA121U/2K5G4 from Texas Instruments (formerly Burr-Brown) is a FET-input, low-power instrumentation amplifier optimized for high-impedance sensor interfaces. It delivers ±4pA input bias current, ±200µV max input offset voltage, 106dB CMR at G=100, and operates from ±2.25V to ±18V supplies - enabling precision signal conditioning in battery-powered ECG, bridge transducer, and portable data acquisition systems.

For engineers reviewing the INA121U/2K5G4 datasheet, INA121U/2K5G4 pinout, INA121U/2K5G4 application, or INA121U/2K5G4 equivalent, key selection criteria include its laser-trimmed gain accuracy (±0.05% at G=100), 50kHz bandwidth at G=100, SOIC-8 package compatibility with industrial temperature range (–40°C to +85°C), and single-resistor programmable gain (1–10,000 V/V).

Technical Context

The INA121U/2K5G4 employs a three-op-amp current-feedback architecture with on-chip 40kΩ/25kΩ resistor networks and laser-trimmed internal feedback resistors (50kΩ total). Its FET input stage enables direct interfacing with >1MΩ source impedances while maintaining 20nV/√Hz input-referred noise at 1kHz and G=100.

Gain is set externally via RG between pins 1 and 8 per G = 1 + 50kΩ/RG. Input overvoltage protection withstands ±40V, and the Ref pin establishes output reference potential - requiring ≤8Ω impedance to preserve >100dB CMR. The device achieves 0.7V/µs slew rate and 35µs 0.01% settling at G=100.

Key Specifications

Pinout & Package

INA121U/2K5G4 is housed in an 8-pin SOIC (SO-8) surface-mount package per JEDEC MS-012 variation AA, with 1.27mm pitch, 3.9mm width, and 1.75mm max height. Pin 1 identifier is located in quadrant Q1 of the tape-and-reel carrier.

Key Features

Applications

Equivalent & Alternatives

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

Compared with INA121U/2K5G4, INA128UA/2K5 offers superior DC precision at higher power cost, while AD8421ARMZ delivers bandwidth and noise advantages but requires additional protection circuitry - making INA121U/2K5G4 the optimal balance for rugged, low-power, high-impedance sensor interfaces.

Availability

INA121U/2K5G4 is available at Aetrix Electronics and suitable for ECG monitoring systems, strain gauge bridge amplifiers, portable gas sensor interfaces, and capacitive touch controller front-ends requiring stable component supply across industrial temperature ranges and long production lifecycles.

Supply support for INA121U/2K5G4 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, low-power, and robust signal-conditioning ICs for industrial, medical, and test equipment markets.

The INA121U/2K5G4 belongs to TI's instrumentation amplifier product line, designed specifically for low-level sensor signal extraction in environments with high common-mode noise, wide supply flexibility, and stringent reliability requirements.

FAQ

What is the maximum gain achievable with INA121U/2K5G4, and how is it configured?

The INA121U/2K5G4 supports gains from 1 V/V to 10,000 V/V using a single external resistor RG connected between pins 1 and 8, per the equation G = 1 + 50kΩ/RG. For G=10,000, RG = 5.001Ω is required; however, practical implementation uses 4.99Ω (1% tolerance). At high gains, wiring resistance and RG temperature coefficient become dominant error sources - INA121U/2K5G4's laser-trimmed internal resistors ensure ±25ppm/°C gain drift regardless of RG choice.

Does INA121U/2K5G4 require external offset trimming in typical applications?

No - the INA121U/2K5G4 is laser-trimmed for ±200µV input offset voltage and ±2µV/°C drift, eliminating the need for external trimming in most applications. Only systems demanding sub-50µV offset (e.g., high-resolution weigh scales) may require optional Ref-pin adjustment using an op-amp buffer, as shown in Figure 2 of the INA121U/2K5G4 datasheet. The Ref pin must remain low-impedance (<8Ω) to preserve CMR performance.

Can INA121U/2K5G4 operate from a single +5V supply?

Yes - the INA121U/2K5G4 functions with supplies as low as ±2.25V (i.e., +4.5V total), including single +5V configurations where V+ = +5V and V– = 0V. In this mode, the input common-mode range is reduced to approximately 1.2V below V+ and 2.1V above V–, and output swing is limited to ~0.3V to ~4.2V. Proper Ref pin biasing (e.g., to 2.5V) is essential to center the output within this range for INA121U/2K5G4 to maintain linearity.

What is the purpose of the overvoltage protection circuitry in INA121U/2K5G4?

The INA121U/2K5G4 integrates internal 25kΩ series resistors and diode clamps on both IN+ and IN– inputs, enabling survival under ±40V continuous input overvoltage conditions without damage. This protects downstream circuitry during sensor disconnection, ESD events, or power-rail faults. The protection operates passively - no external components needed - and does not degrade normal operation, as confirmed by the flat region in the input V/I curve up to ±10V in the INA121U/2K5G4 datasheet.

How does the current-feedback architecture of INA121U/2K5G4 improve dynamic performance?

The INA121U/2K5G4's current-feedback topology decouples bandwidth from gain - delivering 50kHz at G=100 and 5kHz at G=1000, unlike voltage-feedback IAs whose bandwidth drops inversely with gain. This enables fast settling (35µs at 0.01% for G=100) and stable step response even in high-gain configurations. The architecture also minimizes gain-dependent phase shift, preserving signal integrity in time-critical applications like respiratory waveform capture.