Texas Instruments OPA689U/2K5

Overview

OPA689U/2K5 from Texas Instruments (formerly Burr-Brown) is a wideband voltage-feedback operational amplifier with integrated bipolar output voltage limiting, stable for gains ≥ +4, –3dB bandwidth of 280MHz at G = +6, slew rate of 1600V/µs, and ±15mV limiter offset accuracy - used as a fast-recovery ADC input driver or IF limiting amplifier in high-speed data acquisition systems.

For engineers reviewing the OPA689U/2K5 datasheet, OPA689U/2K5 pinout, OPA689U/2K5 application, or OPA689U/2K5 equivalent, key selection criteria include limiting voltage accuracy (±15mV), recovery time from overdrive (2.4ns max), small-signal bandwidth (280MHz @ G=+6), supply flexibility (±5V or +5V), and SO-8 package compatibility with high-density PCB layouts.

Technical Context

The OPA689U/2K5 implements output-stage voltage limiting via dedicated VH and VL pins, enabling precise clamping independent of closed-loop gain configuration. Its decompensated architecture ensures stability only at gains ≥ +4, delivering higher bandwidth and slew rate than unity-gain-stable alternatives like the OPA688.

Limiter operation is decoupled from the op amp's core signal path: limiting engages only when the output approaches preset thresholds, preserving linear-region fidelity and enabling sharp transition (<30mV guardband) between linear and saturated behavior - critical for transimpedance amplifiers and comparator-like signal conditioning.

Key Specifications

Pinout & Package

OPA689U/2K5 is housed in an 8-pin SOIC (SO-8) surface-mount package with industry-standard pinout and thermal resistance of 125°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with OPA688U/2K5 and LMH6723MA/NOPB, the OPA689U/2K5 uniquely combines gain ≥ +4 stability, 280MHz bandwidth, and ±15mV limiter accuracy in a single SO-8 device - making it irreplaceable in high-speed limiting amplifier roles where both speed and precision clamping are simultaneously required.

Availability

OPA689U/2K5 is available at Aetrix Electronics and suitable for high-speed data acquisition, RF receiver front-ends, and precision signal conditioning applications requiring stable component supply, tape-and-reel delivery, and long-term industrial lifecycle support.

Supply support for OPA689U/2K5 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 high-performance analog portfolio, including precision op amps, data converters, and interface ICs.

The OPA689U/2K5 belongs to TI's high-speed voltage-feedback op amp product line, designed specifically for applications demanding fast overdrive recovery, programmable output limiting, and wide bandwidth in compact SO-8 packaging.

FAQ

What is the minimum stable gain for the OPA689U/2K5?

The OPA689U/2K5 is decompensated and stable only for closed-loop gains ≥ +4. Attempting to use it at unity gain or G = +2 will cause oscillation due to insufficient phase margin. For lower-gain applications, the pin-compatible OPA688U/2K5 is specified for stability down to G = +1.

Can the OPA689U/2K5 operate from a single +5V supply?

Yes, the OPA689U/2K5 supports single-supply operation at +5V with VCM = 2.5V. In this mode, VH and VL are referenced to common-mode voltage (e.g., VH = VCM + 1.2V = 3.7V, VL = VCM – 1.2V = 1.3V), and output swing is limited to VCM ± 1.6V (min) under 500Ω load.

What is the maximum capacitive load the OPA689U/2K5 can drive directly?

The OPA689U/2K5 should not drive >2pF capacitive load directly. For loads >2pF, a series isolation resistor (RS) is required - e.g., 125Ω for 100pF, 150Ω for 1000pF - as shown in the RS vs Capacitive Load curve (Figure 8). This prevents peaking and ensures stable step response.

How does limiter feedthrough affect system performance in the OPA689U/2K5?

Limiter feedthrough is –60dB typical at 5MHz, meaning a 1V AC signal on VH or VL couples to the output at ~1mV level. This is negligible in most limiting applications but must be considered in ultra-low-noise systems where limiter control lines run near sensitive nodes.

Is the OPA689U/2K5 pin-compatible with other SO-8 op amps?

The OPA689U/2K5 uses standard SO-8 pinout (pin 1 NC, pins 2/3 inputs, pin 4 –VS, pin 5 VH, pin 6 output, pin 7 +VS, pin 8 VL), matching industry convention. However, functional compatibility requires verification of limiter pin usage, gain stability requirements, and supply configuration - it is not a generic SO-8 op amp replacement.