Texas Instruments OPA137U

Overview

OPA137U from Texas Instruments (formerly Burr-Brown) is a single-channel, FET-input operational amplifier in an SO-8 surface-mount package. It delivers 5pA input bias current, 1.5mV max input offset voltage, 1MHz gain-bandwidth product, ±2.25V to ±18V dual-supply operation, and rail-to-rail input common-mode range extending to V+. It is used in precision photodetector amplifiers and battery-powered instrumentation where low power and high input impedance are critical.

For engineers reviewing the OPA137U datasheet, OPA137U pinout, OPA137U application, or OPA137U equivalent, key selection criteria include its FET-input architecture for ultra-low IB, guaranteed −40°C to +85°C operation, 220µA quiescent current per channel, and compatibility with single-supply systems up to +36V.

Technical Context

The OPA137U employs a JFET-input stage enabling 5pA typical input bias current and 10¹²Ω common-mode input impedance. Its input common-mode voltage range extends from (V−)+3V to V+, supporting high-side sensing without phase reversal - a known failure mode in older TL06x-family amplifiers.

It features unity-gain stability, 3.5V/µs slew rate, and 94dB open-loop gain, enabling fast settling (8µs to 0.1%) into 100pF loads. The device operates across ±2.25V to ±18V supplies (or +4.5V to +36V single supply), with PSRR and CMRR exceeding 76dB over frequency.

Key Specifications

Pinout & Package

OPA137U is housed in an 8-pin SOIC (SO-8) package per JEDEC MS-012, with thermal resistance θ_JA = 150°C/W. Pin numbering follows standard SOIC convention: Pin 1 (top-left corner, marked by notch or dot) is non-inverting input (+In); Pin 8 is V−.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar FET-input op amp applications.

Compared with TL071CP and OPA313IDBVR, the OPA137U uniquely balances ultra-low input bias (5pA), wide supply flexibility (±2.25V to ±18V), and guaranteed industrial temperature operation - making it irreplaceable in legacy industrial instrumentation and high-voltage sensor interfaces.

Availability

OPA137U is available at Aetrix Electronics and suitable for strain gage amplifiers, photodetector amplifiers, and precision integrators requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for OPA137U 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, low-power, and industrial-grade signal conditioning ICs.

The OPA137U belongs to TI's MicroAmplifier™ series - designed specifically for miniature, low-cost, high-input-impedance applications including portable instrumentation, sensor interfaces, and battery-operated precision analog front-ends.

FAQ

What is the maximum capacitive load the OPA137U can drive without instability?

The OPA137U is characterized to drive up to 1000pF capacitive loads while maintaining stability, as confirmed in the datasheet's "Capacitive Load Drive" specification. For loads >100pF, TI recommends adding a small series resistor (e.g., 10–50Ω) between the output and the load to isolate the amplifier from reactive feedback. This preserves phase margin and avoids peaking or oscillation in active filter or cable-driving applications using the OPA137U.

Does the OPA137U support single-supply operation, and what is the minimum usable supply voltage?

Yes, the OPA137U supports true single-supply operation from +4.5V to +36V. At the minimum +4.5V supply, the input common-mode range remains (V−)+3V to V+, meaning inputs must stay ≥3V above ground - requiring appropriate biasing (e.g., mid-rail reference) for AC-coupled signals. The OPA137U's ability to operate down to +4.5V makes it viable in 5V microcontroller-based sensor nodes where the OPA137U serves as a low-power analog front-end.

How does the OPA137U prevent phase inversion when inputs exceed the common-mode range?

The OPA137U uses an input stage architecture that avoids the PNP input transistor structure found in older TL06x op amps - eliminating the phase-reversal failure mode. Even when inputs go beyond (V−)+3V to V+, the OPA137U maintains correct output polarity and linear behavior. This is critical in voltage-follower configurations used in control loops, where phase inversion could cause system instability. The OPA137U's guaranteed behavior under overdrive is explicitly validated and documented in its Applications Information section.

Is the OPA137U pin-compatible with other members of the OPA137 family, such as the OPA137NA in SOT-23-5?

No - the OPA137U (SO-8) is not pin-compatible with the OPA137NA (SOT-23-5). The SO-8 package has eight pins with NC terminals at pins 5, 6, and 8, while the SOT-23-5 uses a 5-pin layout (V+, −In, Out, V−, +In) with no NC pins. Board redesign is required to substitute between packages. However, electrical specifications (offset, IB, GBW, etc.) are identical across OPA137 variants, so schematic-level functional replacement is valid when layout permits.

What is the thermal resistance (θ_JA) of the OPA137U in its SO-8 package, and how does it affect power dissipation?

The OPA137U in SO-8 package has a junction-to-ambient thermal resistance (θ_JA) of 150°C/W, as specified in the Thermal Resistance table. With a maximum quiescent current of 270µA per channel at +85°C and ±15V supplies, total power dissipation is ~8.1mW - resulting in a junction temperature rise of just 1.2°C above ambient. This low self-heating ensures stable DC performance in precision applications and confirms the OPA137U's suitability for thermally constrained PCB layouts without heatsinking.