Texas Instruments INA111APG4

Overview

INA111APG4 from Texas Instruments (formerly Burr-Brown) is a high-speed, FET-input instrumentation amplifier designed for precision signal conditioning in noisy, high-impedance sensor interfaces. It delivers 4 µs settling time to 0.01% at G = 100, 106 dB minimum CMRR at G = 100, and ±500 µV max input offset voltage over temperature - enabling accurate extraction of microvolt-level biopotential or bridge transducer signals in medical and industrial DAQ systems.

For engineers reviewing the INA111APG4 datasheet, INA111APG4 pinout, INA111APG4 application, or INA111APG4 equivalent, key selection criteria include its current-feedback topology (2 MHz bandwidth at G = 1), laser-trimmed DC accuracy, 20 pA max input bias current, and compatibility with single-resistor gain programming (G = 1 + 50 kΩ/R_G) across 1–1000 range.

Technical Context

The INA111APG4 employs a three-op-amp current-feedback architecture with internal 10 kΩ/25 kΩ resistor networks, enabling extended bandwidth and fast settling independent of gain configuration. Its FET-input stage achieves 10¹² Ω || 6 pF input impedance and sub-20 pA bias current, minimizing loading on high-Z sources like piezoelectric sensors or thermocouples.

Gain is set by a single external resistor (R_G) connected between pins 1 and 8; the 50 kΩ term derives from laser-trimmed on-chip metal-film resistors. Output is referenced to the Ref pin (pin 5), requiring low-impedance grounding to preserve CMRR - a 2 Ω series resistance degrades 90 dB CMRR to ~80 dB at G = 1.

Key Specifications

Pinout & Package

INA111APG4 is supplied in an 8-pin plastic DIP (PDIP) package with 0.3-inch width, RoHS-compliant NiPdAu lead finish, and through-hole mounting compatibility. Pin 1 is marked with a notch or dot; device orientation follows standard DIP top-view labeling.

Key Features

Applications

Equivalent & Alternatives

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

Compared with INA111APG4, INA128P trades speed for femtoampere bias current - critical for electrochemical sensors but excessive for most bridge/thermocouple use cases - while AD620ANZ sacrifices 6 dB CMRR and 450 µV offset headroom to achieve broader operating temperature and lower unit cost.

Availability

INA111APG4 is available at Aetrix Electronics and suitable for medical instrumentation, industrial data acquisition, and precision sensor interface applications requiring stable component supply, long-term lifecycle support, and traceable sourcing from authorized channels.

Supply support for INA111APG4 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-performance signal conditioning ICs for industrial, medical, and test equipment markets.

The INA111APG4 belongs to TI's legacy instrumentation amplifier product line, engineered specifically for high-speed, low-drift amplification of weak differential signals in electrically hostile environments - such as hospital-grade patient monitors and factory-floor vibration analyzers.

FAQ

What is the maximum gain achievable with the INA111APG4 using external resistor programming?

The INA111APG4 supports gains from 1 to 1000 using a single external resistor R_G, per the equation G = 1 + 50 kΩ/R_G. At R_G = 49.9 Ω, gain reaches 1000; the datasheet confirms this is the maximum specified gain. While theoretical calculation permits higher values (e.g., R_G = 5 Ω → G ≈ 10,001), the INA111APG4's performance - including bandwidth, settling time, and CMRR - is only guaranteed up to G = 1000. For gains beyond that, the INA111APG4 is not characterized or recommended.

Can the INA111APG4 operate from a single +5V supply?

No, the INA111APG4 requires dual supplies (±6 V to ±18 V) and is not specified for single-supply operation. Its input common-mode range extends only to ±10 V at T_A = +25°C, and output swing is limited to ±11 V minimum into 2 kΩ - both dependent on symmetric rails. Attempting single +5 V operation would violate absolute maximum ratings (e.g., input voltage exceeding V– – 0.7 V), risk latch-up, and yield no functional output. For single-supply designs, consider TI's INA333 or ADI's AD8421 as alternatives.

How does the Ref pin (Pin 5) affect common-mode rejection in the INA111APG4?

The Ref pin (Pin 5) establishes the output reference potential and directly impacts CMRR in the INA111APG4. A series impedance >2 Ω on this pin degrades CMRR by up to 10 dB - for example, a typical 90 dB CMRR drops to ~80 dB at G = 1. This occurs because the Ref path forms part of the common-mode feedback loop. To preserve rated CMRR, the Ref pin must connect to a low-impedance ground (e.g., dedicated ground plane trace, not daisy-chained via other components) and avoid routing near noisy digital lines. The INA111APG4's datasheet explicitly warns against using resistive dividers or RC filters on Ref.

Is the INA111APG4 pin-compatible with the INA111BP or INA111AU variants?

The INA111APG4 shares identical pinout and electrical specifications with the INA111BP (same DIP-8 package and –40°C to +85°C rating), making them functionally interchangeable. However, it is not pin-compatible with the INA111AU (16-pin SOIC), which has different pin assignments - notably separate output sense (Pin 12) and relocated R_G terminals. Substituting INA111APG4 for INA111AU requires PCB redesign due to package size, pin count, and terminal mapping differences; no adapter or drop-in replacement is possible.

What is the recommended layout practice for maintaining high CMRR with the INA111APG4?

To maintain the INA111APG4's rated CMRR, route the V_IN+ (Pin 3) and V_IN– (Pin 2) traces as a tightly coupled, equal-length differential pair - ideally side-by-side over a solid ground plane. Avoid vias, stubs, or connectors between source and pins. Place 0.1 µF decoupling capacitors within 2 mm of Pins 4 (V–) and 6 (V+), and tie the Ref pin (Pin 5) directly to the ground plane with a short, wide trace (<5 mm). Any asymmetry >0.5 mm in trace length or >10% in capacitance mismatch degrades high-frequency CMRR, as confirmed by the "Common-Mode Rejection vs Frequency" curve in the INA111APG4 datasheet.