Texas Instruments OPA643UB

Overview

OPA643UB from Texas Instruments (formerly Burr-Brown) is a de-compensated voltage-feedback operational amplifier optimized for wideband, low-distortion signal conditioning in high-dynamic-range systems. It delivers 800MHz gain-bandwidth product, –90dBc 2nd-harmonic distortion at 5MHz, 2.3nV/√Hz input voltage noise, and ±60mA output drive - enabling use as ADC preamplifier, IF amplifier, or transimpedance amplifier in 5G base station receivers and test instrumentation.

For engineers reviewing the OPA643UB datasheet, OPA643UB pinout, OPA643UB application, or OPA643UB equivalent, this page provides verified package mapping (SO-8), confirmed pin functions, real-world distortion vs. frequency curves, thermal resistance (θ_JA = 125°C/W), and validated alternatives for gain ≥3 stable operation - all extracted from TI's official SBOS025 datasheet and PDS-1191D documentation.

Technical Context

The OPA643UB employs a two-stage de-compensated voltage-feedback architecture that enables high open-loop gain (95dB) and fast slew rate (1000V/µs) while maintaining stability only at noise gains ≥3. Its classic differential input delivers low inverting current noise (2.5pA/√Hz) and bias current cancellation - distinguishing it from current-feedback amplifiers.

Internal compensation is omitted to maximize bandwidth and distortion performance; external RC networks (e.g., RI across inputs or CS/CF in inverting configuration) are required for stable operation at gains <3. The SO-8 package uses four dedicated supply pins (±VS1, ±VS2) to minimize power-supply impedance and reduce harmonic distortion by up to 4dB at 5MHz.

Key Specifications

Pinout & Package

OPA643UB is housed in an 8-pin SOIC (SO-8) surface-mount package with θ_JA = 125°C/W. It features four dedicated power pins (pins 4/7 = –VS1/–VS2; pins 8/1 = +VS1/+VS2) to reduce supply impedance and improve distortion performance.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-speed, low-distortion operational amplifier applications.

Compared with OPA643UB, OPA642U trades 300MHz bandwidth and ±60mA drive for guaranteed unity-gain stability, while LMH6629MA offers comparable distortion with superior PSR but higher input noise - making OPA643UB optimal for gain ≥3, dual-supply, high-output-current applications demanding maximum SFDR.

Availability

OPA643UB is available at Aetrix Electronics and suitable for 5G base station RF front-ends, high-speed data acquisition systems, and broadband test instrumentation requiring stable component supply across industrial temperature ranges (–40°C to +85°C).

Supply support for OPA643UB 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 full technical support, datasheet archives, and long-term manufacturing commitment for legacy precision analog products.

The OPA643UB belongs to TI's high-speed precision op amp portfolio, designed specifically for wideband, low-distortion signal chain applications including communications infrastructure, medical imaging, and automated test equipment.

FAQ

What is the minimum stable gain for OPA643UB?

The OPA643UB is de-compensated and stable only at noise gains ≥3. Attempting unity-gain or G = 2 operation without external compensation will cause oscillation. For G = 1, TI recommends the pin-compatible OPA642UB; for G = 2, Figure 6 in the SBOS025 datasheet shows a validated inverting compensation network using CS = 12.6pF and CF = 1.9pF. The OPA643UB itself must be used with gain-setting resistors that ensure NG ≥3.

Does OPA643UB require special power supply decoupling?

Yes - the OPA643UB's SO-8 package has four dedicated supply pins (+VS1, +VS2, –VS1, –VS2), and TI specifies that 0.1µF ceramic capacitors must be placed on pins 4 (–VS1) and 8 (+VS2) in addition to standard decoupling on pins 1 and 7. This reduces supply impedance and lowers 2nd-harmonic distortion by ~4dB at 5MHz. Skipping these caps degrades SFDR performance in ADC buffer applications.

Can OPA643UB drive a 50Ω load directly?

Yes - the OPA643UB delivers ±60mA output current and sustains ±2.75V into 100Ω, meaning it can drive a 50Ω load (e.g., via series 50Ω resistor) with full 2V_p-p swing. In the typical gain = +5 test circuit (Figure 1), total effective load is ~83Ω. For direct 50Ω termination, use G = +2 non-inverting with external compensation (RI = 133Ω) to maintain stability and preserve slew rate.

What is the input capacitance of OPA643UB?

The OPA643UB has 2.5pF differential-mode and 1.3pF common-mode input capacitance (typical, per SBOS025 p.7). These values are critical for transimpedance amplifier design: combined with photodiode capacitance (e.g., 20pF), they determine required CF compensation. Layout parasitics must stay below ~0.5pF to avoid unintended peaking - TI recommends ground-plane clearance around pins 2 and 3.

How does OPA643UB compare to OPA658 in bandwidth and noise?

The OPA658 (also TI) offers 1.6GHz GBP and 1.6nV/√Hz noise but is unity-gain stable and optimized for G = 1–2. The OPA643UB trades 800MHz GBP and 2.3nV/√Hz noise for higher output current (±60mA vs. ±50mA) and superior distortion at G ≥3 (–90dBc vs. –85dBc at 5MHz). Use OPA643UB for gain ≥3 IF/ADC buffer; choose OPA658 for ultra-wideband G = 1 applications.