Texas Instruments OPA228UA

Overview

OPA228UA from Texas Instruments is a high-precision, low-noise dual operational amplifier optimized for closed-loop gains ≥5, delivering 33 MHz unity-gain bandwidth, 10 V/µs slew rate, and 75 µV maximum input offset voltage across –40°C to +85°C. It operates from ±2.5 V to ±18 V supplies and targets professional audio amplifiers, spectrum analyzers, and precision data acquisition systems where wide bandwidth and low distortion are critical.

For engineers reviewing the OPA228UA datasheet, OPA228UA pinout, OPA228UA application, or OPA228UA equivalent, key selection criteria include minimum closed-loop gain requirement (≥5), thermal performance in SOIC-8 (R_θJA = 110.1°C/W), input voltage noise density (3 nV/√Hz at 1 kHz), and compatibility with industry-standard OP37 footprints.

Technical Context

The OPA228UA uses a compensated bipolar input stage enabling stable operation only at closed-loop gains of 5 V/V or higher-unlike its unity-gain-stable OPA227 counterpart. Its architecture delivers high open-loop gain (160 dB) and exceptional common-mode rejection (138 dB), supporting precision DC-coupled signal chains requiring minimal drift over temperature.

It features dual independent amplifiers in an 8-pin SOIC package with dedicated offset trim pins (1 and 8), non-inverting/inverting inputs per channel, and rail-to-rail output swing limited to (V–)+2 V to (V+)+2 V under 10 kΩ load-optimized for high-fidelity AC signal processing with low THD+N (0.00005% at 1 kHz).

Key Specifications

Pinout & Package

OPA228UA is housed in an 8-pin SOIC (SO-8) package with exposed pad not present; thermal resistance R_θJA = 110.1°C/W enables standard PCB layout without forced air in ambient ≤ 50°C environments.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-speed precision op amp applications.

Compared with OPA228U and OPA211AIDR, the OPA228UA uniquely balances SOIC-8 manufacturability, ±18 V dual-supply flexibility, and 33 MHz bandwidth at G ≥ 5-making it optimal for cost-sensitive, thermally constrained industrial instruments requiring proven OP37 pin compatibility.

Availability

OPA228UA is available at Aetrix Electronics and suitable for professional audio amplifier (rack mount), spectrum analyzer, and industrial AC-DC power monitor applications requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for OPA228UA 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 specializing in analog and embedded processing technologies, with decades of expertise in precision op amps and signal-chain solutions.

The OPAx228 product line was designed for high-fidelity AC-coupled instrumentation demanding simultaneous wide bandwidth, low noise, and dc precision-targeting test & measurement, professional audio, and industrial sensing.

FAQ

What is the minimum closed-loop gain required for stable operation of the OPA228UA?

The OPA228UA requires a minimum closed-loop gain of 5 V/V for stable operation. Unlike unity-gain-stable amplifiers such as the OPA227, the OPA228UA's internal compensation is optimized for higher gains to achieve its 33 MHz bandwidth and 10 V/µs slew rate. Using it at G < 5 may cause peaking, ringing, or oscillation. Always verify phase margin in simulation or bench testing when operating near the gain boundary.

Can the OPA228UA operate from a single 30-V supply instead of dual ±15-V rails?

Yes, the OPA228UA supports single-supply operation up to 36 V (V+ to V−), including 30-V configurations. However, input common-mode range is limited to (V−)+2 V to (V+)-2 V, and output swing is similarly rail-restricted. For true 0–30 V signal handling, level-shifting or external biasing is required. The device's specified performance (e.g., noise, THD+N) is validated under dual-supply conditions per the datasheet.

How does the OPA228UA's offset trim functionality work across both channels?

The OPA228UA provides independent offset trim pins for each channel: Pin 1 adjusts Channel A offset, and Pin 8 adjusts Channel B offset. Each connects to an internal resistive divider network; a 10-kΩ potentiometer between Pins 1 and 8 with wiper to V− calibrates both channels simultaneously, while separate pots enable individual trimming. Leaving either pin unconnected results in nominal offset performance (±75 µV max).

Is the OPA228UA pin-compatible with the OP37, and what improvements does it offer?

Yes, the OPA228UA is a pin-for-pin replacement for the OP37 in SOIC-8 (U) and PDIP-8 (P) packages. It improves upon the OP37 with 33 MHz bandwidth (vs 63 MHz GBW but lower usable AC performance), 10 V/µs slew rate (vs 17 V/µs but with lower distortion), 75 µV max offset (vs 125 µV), and 138 dB CMRR (vs 110 dB). Its enhanced noise (3 nV/√Hz vs 10 nV/√Hz) and thermal drift (±0.6 µV/°C vs ±2 µV/°C) make it superior for precision AC applications.

What decoupling capacitance is recommended for the OPA228UA power pins?

Texas Instruments recommends a 0.1-µF ceramic capacitor placed as close as possible to each power pin (Pins 4 and 7) of the OPA228UA, with short traces to minimize inductance. For systems with noisy supplies or high-frequency switching regulators, adding a parallel 4.7-µF tantalum or aluminum electrolytic capacitor at the board-level power entry improves low-frequency PSRR. Avoid oversized ceramics (>1 µF) directly at the pin due to potential resonance with trace inductance.