Texas Instruments INA821ID

Overview

INA821ID from Texas Instruments is a precision instrumentation amplifier with 35-µV maximum input offset voltage, 7-nV/√Hz input voltage noise, and 4.7-MHz bandwidth at G = 1. It features ±40-V input overvoltage protection, 112-dB minimum CMRR at G = 10, and operates from ±2.25 V to ±18 V dual supplies - ideal for ECG front-ends and industrial analog input modules.

For engineers reviewing the INA821ID datasheet, INA821ID pinout, INA821ID application, or INA821ID equivalent, key selection criteria include gain-setting resistor configuration (RG pins 2 & 3), thermal performance in SOIC package (RθJA = 119.6°C/W), input stage super-beta transistor architecture enabling low drift (0.4 µV/°C max), and compatibility with 1-nF capacitive loads without instability.

Technical Context

The INA821ID uses a three-op-amp topology with super-beta input transistors to achieve ultra-low input bias current (0.15–0.5 nA) and minimal offset drift. Its gain is set externally via a single resistor between pins 2 and 3 using G = 1 + 49.4 kΩ/RG, supporting gains from 1 to 10,000.

Input overvoltage protection circuitry clamps signals up to ±40 V relative to supply rails, while the REF pin provides direct reference injection with 10-kΩ input impedance and unity gain to output. The device maintains 112 dB CMRR at G = 10 across DC–60 Hz with full common-mode range compliance.

Key Specifications

Pinout & Package

INA821ID is housed in an 8-pin SOIC package (4.90 mm × 3.91 mm body size) with exposed thermal pad internally connected to –VS. Pin 1 is –IN, pin 4 is +IN, pin 7 is OUT, pins 2 & 3 are RG (gain-setting resistor terminals), pin 6 is REF, pin 5 is –VS, and pin 8 is +VS.

Key Features

Applications

Equivalent & Alternatives

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

Compared with INA828IDR and INA819IDGKR, the INA821ID delivers the lowest input offset voltage and best low-frequency noise performance among TI's 8-pin instrumentation amplifiers, making it preferred for high-precision medical and test equipment where signal integrity is non-negotiable.

Availability

INA821ID is available at Aetrix Electronics and suitable for ECG front-ends, industrial analog input modules, and flow transmitter designs requiring stable component supply, long-term manufacturability, and guaranteed TI production continuity through 2030.

Supply support for INA821ID 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 leader delivering analog and embedded processing solutions for industrial, automotive, and personal electronics markets.

The INA821ID belongs to TI's precision instrumentation amplifier product line, engineered for high-accuracy signal conditioning in medical diagnostics, process control, and automated test equipment where low drift, low noise, and robust input protection are mandatory.

FAQ

What is the maximum gain achievable with the INA821ID?

The INA821ID supports gains from 1 to 10,000 using a single external resistor between pins 2 and 3 per the equation G = 1 + 49.4 kΩ/RG. At G = 10,000, RG = 4.94 Ω - requiring careful layout and low-tolerance resistor selection. Bandwidth reduces to 30 kHz at this gain, limiting use to DC or low-frequency applications. The INA821ID maintains stability and specified performance across this full range.

Does the INA821ID require external compensation for capacitive loads?

No, the INA821ID is internally compensated and remains stable with capacitive loads up to 1000 pF, as confirmed in the datasheet's "Load capacitance stability" specification. This eliminates need for external series resistors or compensation networks when driving ADC input filters, coaxial cables, or multiplexed sensor arrays - a key advantage over older instrumentation amplifiers requiring external stabilization.

How does the REF pin function in the INA821ID?

The REF pin on the INA821ID provides a unity-gain, buffered reference input that directly offsets the output voltage. It has 10-kΩ input impedance and must be driven by a low-impedance source (≤100 Ω) to prevent gain error and noise coupling. Unlike some competitors, the INA821ID's REF path exhibits no gain-dependent attenuation - ensuring precise level-shifting across all gain settings without recalibration.

What thermal considerations apply to the INA821ID in SOIC package?

The INA821ID in SOIC (D package) has a junction-to-ambient thermal resistance (RθJA) of 119.6°C/W. At 650 µA quiescent current and ±15-V supplies, power dissipation is ~19.5 mW, resulting in ~2.3°C junction rise above ambient. For high-temperature operation (e.g., +125°C ambient), ensure adequate copper pour on –VS-connected thermal pad and avoid stacking heat-generating components nearby to maintain reliability within the 175°C max junction limit.

Can the INA821ID operate from a single 5-V supply?

Yes, the INA821ID supports single-supply operation from 4.5 V to 36 V. At 5-V supply, the input common-mode range extends from (V–) + 2 V to (V+) – 2 V, i.e., 2 V to 3 V, and output swing reaches within 150 mV of each rail. For rail-to-rail input/output, consider TI's INA333 - but the INA821ID remains optimal where its superior CMRR, lower noise, and overvoltage protection justify the limited common-mode range.