Texas Instruments OPA228PAG4

Overview

OPA228PAG4 from Texas Instruments is a dual-channel, high-precision, low-noise 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. It operates from ±2.5 V to ±18 V supplies and targets precision analog signal conditioning in professional audio and spectrum analysis systems.

For engineers reviewing the OPA228PAG4 datasheet, OPA228PAG4 pinout, OPA228PAG4 application, or OPA228PAG4 equivalent, key selection criteria include its gain-stability requirement (G ≥ 5), low 3 nV/√Hz input voltage noise at 1 kHz, 138 dB CMRR, and DIP-8 package compatibility with legacy OP37 footprints.

Technical Context

The OPA228PAG4 uses a compensated bipolar input stage enabling stable operation only at closed-loop gains of 5 V/V or higher - unlike the unity-gain-stable OPA227. Its internal compensation trades off low-frequency precision for high-speed transient response, yielding 1.5 µs settling time to 0.1% for a 10-V step.

This device features laser-trimmed input offset voltage, matched input bias current (≤10 nA), and rail-to-rail output swing capability within 2 V of supply rails under 10-kΩ load - critical for wide-dynamic-range data acquisition front-ends operating across –40°C to +85°C.

Key Specifications

Pinout & Package

OPA228PAG4 is housed in an 8-pin PDIP (Plastic Dual In-line Package) with 0.3-inch body width and through-hole mounting. Pin 1 is offset trim (not connected by default), pins 2 and 3 are inverting/non-inverting inputs, pin 4 is V–, pin 5 is NC (no internal connection), pin 6 is output, pin 7 is V+, and pin 8 is second offset trim terminal.

Key Features

Applications

Equivalent & Alternatives

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

Compared with OPA228PA and AD827JRZ, the OPA228PAG4 uniquely combines DIP-8 mechanical compatibility with industry-leading 33 MHz bandwidth and 3 nV/√Hz noise - making it optimal for high-fidelity test equipment upgrades where layout change is constrained.

Availability

OPA228PAG4 is available at Aetrix Electronics and suitable for professional audio equipment, spectrum analyzer front-ends, and industrial AC-DC monitoring systems requiring stable component supply with long-term obsolescence management.

Supply support for OPA228PAG4 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 U.S.-based semiconductor company specializing in analog and embedded processing technologies, with leadership in precision amplifiers, data converters, and power management ICs.

The OPAx228 product line was designed specifically for high-fidelity signal chains demanding simultaneous ac performance and dc precision - targeting test & measurement, professional audio, and industrial DAQ applications.

FAQ

What is the minimum closed-loop gain required for stable operation of the OPA228PAG4?

The OPA228PAG4 requires a minimum closed-loop gain of 5 V/V for stable operation. Unlike unity-gain-stable amplifiers such as the OPA227, this device's internal compensation is optimized for higher gains to achieve its 33 MHz bandwidth and 10 V/µs slew rate. Operating below G = 5 risks peaking or oscillation, especially with capacitive loads.

Does the OPA228PAG4 support single-supply operation?

Yes, the OPA228PAG4 supports single-supply operation with a total supply voltage range of 4.5 V to 36 V. When used in single-supply mode (e.g., V– = 0 V, V+ = 15 V), its input common-mode range extends from 2 V above V– to 2 V below V+, and output swings within 2 V of each rail under 10-kΩ load - enabling direct interfacing with microcontroller ADCs.

What is the purpose of pins 1 and 8 on the OPA228PAG4?

Pins 1 and 8 on the OPA228PAG4 are offset voltage trim terminals. Connecting a 10-kΩ potentiometer between them - with the wiper tied to V– - allows manual nulling of input offset voltage to <5 µV. This is optional; leaving both pins unconnected maintains the factory-trimmed ±75 µV max offset specification.

How does the OPA228PAG4 compare to the industry-standard OP37 in terms of pin compatibility and performance?

The OPA228PAG4 is a pin-for-pin replacement for the OP37 in PDIP-8 packages, sharing identical pinout and footprint. It improves upon the OP37 with 33 MHz bandwidth (vs 63 MHz GBW but lower noise), 10 V/µs slew rate (vs 17 V/µs), and significantly lower 3 nV/√Hz input voltage noise (vs 4.5 nV/√Hz), while maintaining compatible input bias current and supply range.

Can the OPA228PAG4 drive capacitive loads, and what is the recommended approach?

The OPA228PAG4 can drive capacitive loads up to 100 pF stably in G ≥ 5 configurations. For larger loads (e.g., ADC input capacitance or cable termination), insert a 20–100 Ω isolation resistor between the output pin and the load. This preserves phase margin by separating the amplifier's output impedance from the capacitive reactance - verified in Figure 6-31 of the datasheet.