Texas Instruments OPA228U

Overview

OPA228U 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 3 nV/√Hz input voltage noise density. It operates from ±2.5 V to ±18 V supplies and targets professional audio amplifiers, spectrum analyzers, and precision data acquisition systems requiring simultaneous AC fidelity and DC accuracy.

For engineers reviewing the OPA228U datasheet, OPA228U pinout, OPA228U application, or OPA228U equivalent, key selection criteria include its minimum stable gain of 5 V/V, 138 dB CMRR, 160 dB open-loop gain, –40°C to +85°C operating range, and SOIC-8 package compatibility with industry-standard OP37 footprints.

Technical Context

The OPA228U uses a compensated bipolar input stage enabling high-speed operation while maintaining precision DC performance. Its internal compensation is tailored for closed-loop gains ≥5 - unlike the unity-gain-stable OPA227 - resulting in higher bandwidth (33 MHz) and faster settling (1.5 µs to 0.1%).

It features laser-trimmed input offset voltage (±75 µV max), ultra-low drift (±0.6 µV/°C max), and high common-mode rejection (138 dB) over frequency, making it suitable for high-dynamic-range signal conditioning where both wideband response and dc stability are required.

Key Specifications

Pinout & Package

OPA228U is housed in an 8-pin SOIC (SO-8) package with standard dual op-amp pinout and two unused offset trim pins. Thermal resistance is R_θJA = 110.1°C/W, supporting operation up to +85°C ambient with moderate PCB copper area.

Key Features

Applications

Equivalent & Alternatives

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

Compared with OPA227U and AD827ARZ, the OPA228U uniquely balances 33 MHz bandwidth, 3 nV/√Hz noise, and ±75 µV offset - making it optimal for applications demanding both high-speed settling and sub-100 µV dc accuracy without external trimming.

Availability

OPA228U is available at Aetrix Electronics and suitable for professional audio equipment, spectrum analyzer front-ends, and precision data acquisition systems requiring stable component supply and long-term manufacturability.

Supply support for OPA228U 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 specifically for high-fidelity, wideband precision applications - bridging the gap between traditional low-noise op-amps and high-speed amplifiers while maintaining dc accuracy.

FAQ

What is the minimum closed-loop gain required for stable operation of the OPA228U?

The OPA228U requires a minimum closed-loop gain of 5 V/V for stable operation. Unlike unity-gain-stable amplifiers such as the OPA227U, it is internally compensated for higher gains to achieve its 33 MHz bandwidth and 10 V/µs slew rate. Using it at G < 5 may cause peaking or oscillation.

Does the OPA228U support single-supply operation?

Yes, the OPA228U supports single-supply operation from 4.5 V to 36 V. Its input common-mode range extends to within 2 V of each rail, and output swings to within 2 V of each supply under light load - enabling use in 5-V or 12-V single-rail systems with appropriate level-shifting.

What is the thermal resistance (R_θJA) of the OPA228U in SOIC-8 package?

The OPA228U in SOIC-8 (D) package has a junction-to-ambient thermal resistance (R_θJA) of 110.1°C/W, as specified in TI's SBOS110C datasheet. This value assumes standard JEDEC 2S2P test board conditions; actual performance improves with added PCB copper pour or thermal vias.

Can the OPA228U replace the OP37 in existing designs?

Yes, the OPA228U is a pin-for-pin replacement for the OP37 in SOIC-8 and PDIP-8 packages, offering substantial improvements: 33 MHz vs 63 MHz GBW (OP37 is 63 MHz, but OPA228U is 33 MHz - correction: OP37 GBW is ~63 MHz, OPA228U is 33 MHz; however, OPA228U provides lower noise, better CMRR, and improved dc specs). Always verify stability at target gain and load conditions per layout.

What is the maximum capacitive load the OPA228U can drive without compensation?

The OPA228U can safely drive up to 100 pF without external compensation, as confirmed by typical overshoot and step-response data in the datasheet. For loads >100 pF, a small series resistor (10–50 Ω) at the output or feedback network adjustment is recommended to maintain phase margin.