Texas Instruments INA126P

Overview

INA126P from Texas Instruments is a single-channel, micropower instrumentation amplifier designed for precision differential signal acquisition in low-power industrial and medical sensor interfaces. It delivers 250 μV max offset voltage, 3 μV/°C max drift, 35 nV/√Hz input voltage noise, ±1.35 V to ±18 V dual-supply operation, and gain programmability from 5 V/V to 10,000 V/V via external resistor - enabling high-accuracy measurement in battery-powered ECG monitors and flow transmitters.

For engineers reviewing the INA126P datasheet, INA126P pinout, INA126P application, or INA126P equivalent, this page provides verified technical context, exact pin functions for the 8-pin PDIP package, real-world application constraints (e.g., Ref pin impedance impact on CMR), and two validated alternative parts with documented functional and packaging differences.

Technical Context

The INA126P uses a two-op-amp topology that reduces quiescent current to 175 μA/channel while maintaining balanced, high-input impedance (≥1 GΩ) and laser-trimmed internal 40 kΩ/10 kΩ resistor network. Its gain equation G = 5 + 80 kΩ/R_G relies on thermally matched internal metal-film resistors with specified drift contribution.

Input stage common-mode range is constrained by internal op-amp A2's output swing limit (±0.7 V from rails); exceeding it saturates A2 and invalidates output regardless of A1 linearity. The REF pin must be driven at low impedance (<8 Ω) to preserve ≥80 dB CMRR - a design-critical interface not abstracted in generic amplifier descriptions.

Key Specifications

Pinout & Package

INA126P is housed in an 8-pin plastic dual in-line package (PDIP), with through-hole mounting and 0.3-inch body width. Pin spacing is 0.1 inch, compatible with standard prototyping and legacy PCB footprints.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD620ARZ and INA333AIDR, the INA126P uniquely balances micropower operation, PDIP package availability, and flexible REF-based output referencing - making it optimal for cost-sensitive, battery-constrained industrial sensor nodes where moderate precision suffices.

Availability

INA126P is available at Aetrix Electronics and suitable for level transmitters, ECG monitors, AC charging station sensor interfaces, and multiparameter patient monitors requiring stable component supply across long production lifecycles.

Supply support for INA126P 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 company specializing in analog and embedded processing technologies, with leadership in precision signal chain solutions for industrial, automotive, and medical markets.

The INA126P belongs to TI's INAx126 micropower instrumentation amplifier family, engineered for accurate, low-noise differential signal acquisition in portable and battery-operated instrumentation systems.

FAQ

What is the maximum gain achievable with the INA126P, and how is it set?

The INA126P supports gains from 5 V/V to 10,000 V/V using a single external resistor RG connected between pins 1 and 8. The gain equation is G = 5 + 80 kΩ/R_G. For G = 10,000, RG = 8.0 Ω (7.87 Ω 1% standard value). At high gains, wiring resistance and socket contact resistance introduce measurable error - direct soldering of RG is recommended for G ≥ 100. The INA126P datasheet Table 7-1 lists standard RG values for common gains.

How does the REF pin affect common-mode rejection in the INA126P?

The REF pin directly offsets the INA126P output: VO = G·(V+IN – V–IN) + V_REF. Its source impedance critically impacts CMRR - a series resistance of just 8 Ω degrades typical CMRR from 94 dB to ~80 dB. To maintain specification, drive REF with a low-impedance buffer (e.g., OPA237) or connect directly to ground/mid-supply via short, wide traces. Never leave REF floating or drive it through high-value resistors.

Can the INA126P operate from a single 3.3V supply, and what are the key constraints?

Yes, the INA126P operates from single supplies as low as 2.7 V. Key constraints include: (1) REF must be biased at mid-supply (e.g., 1.65 V) to center the output swing; (2) input common-mode range shrinks - at 3.3 V, V_CM is limited to ~0.3 V to 3.0 V; (3) output swing is reduced to ~0.75 V from rails. Figure 5-7 in the INA126P datasheet shows exact V_CM vs. V_O boundaries for 3.3 V operation.

What is the impact of input bias current on sensor interfacing with the INA126P?

The INA126P has max input bias current of 25 nA, flowing *out* of both inputs. Without a return path, inputs float beyond common-mode range causing saturation. For low-impedance sources (e.g., Wheatstone bridges), tie one input to REF via a resistor. For high-Z sources (e.g., thermocouples), use matched 47 kΩ resistors from each input to REF to balance bias currents and minimize offset. Unbalanced paths degrade CMRR and increase offset drift.

How does the two-op-amp architecture of the INA126P differ from traditional three-op-amp instrumentation amplifiers?

Unlike three-op-amp IAs, the INA126P uses two op-amps: one differential pair (A1) and one output amplifier (A2). This cuts quiescent current nearly 5× (175 μA vs. ~1 mA) and simplifies gain setting (single RG). However, A2's output swing limits the input common-mode range - a trade-off documented in INA126P Figure 5-6. The two-op-amp design also eliminates the need for matched resistor networks external to the die, improving gain accuracy over temperature.