Texas Instruments OPA643N/3K

Overview

OPA643N/3K from Texas Instruments (formerly Burr-Brown) is a decompensated 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, transimpedance amplifier, or IF buffer in 20MSPS digitizers and broadband instrumentation.

For engineers reviewing the OPA643N/3K datasheet, OPA643N/3K pinout, OPA643N/3K application, or OPA643N/3K equivalent, this page provides verified technical context, SOT23-5 package mapping, confirmed pin functions, real-world distortion vs. frequency behavior, and validated alternative options for gain ≥3 stable high-speed amplification.

Technical Context

The OPA643N/3K employs a two-stage decompensated 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 differential input stage provides 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 minimize distortion; external RC networks (e.g., CS/CF in inverting configuration) are required for low-gain operation (<3), enabling controlled 2nd-order Butterworth response without settling tails. The SOT23-5 variant uses shorter bond wires than SO-8 or DIP packages, yielding superior 5MHz harmonic distortion performance with only two supply pins.

Key Specifications

Pinout & Package

OPA643N/3K is packaged in a 5-pin SOT23-5 surface-mount case (θ_JA = 150°C/W), optimized for low parasitic inductance and minimal distortion. Pin 1 = Non-Inverting Input, Pin 2 = Inverting Input, Pin 3 = Output, Pin 4 = –V_S, Pin 5 = +V_S. No enable or shutdown pins; all pins electrically active.

Key Features

Applications

Equivalent & Alternatives

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

Compared with OPA643N/3K, OPA642U trades 800MHz bandwidth and –90dBc distortion for unity-gain stability and lower noise floor, while LMH6629MA offers higher GBP but requires SO-8 layout and delivers less distortion suppression at 5MHz - making OPA643N/3K optimal for compact, high-SFDR 20MSPS signal chains.

Availability

OPA643N/3K is available at Aetrix Electronics and suitable for high-speed data acquisition, RF instrumentation, optical sensing, and broadcast video systems requiring stable component supply across extended temperature ranges (–40°C to +85°C).

Supply support for OPA643N/3K 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 legacy support for precision high-speed analog products. TI is a global leader in analog IC design with emphasis on signal chain integrity and manufacturability.

The OPA643N/3K belongs to TI's OPA high-speed op amp family, engineered specifically for wideband, low-distortion signal conditioning in test & measurement, communications infrastructure, and medical imaging systems where dynamic range exceeds 80dB.

FAQ

What is the minimum stable gain for OPA643N/3K?

The OPA643N/3K is decompensated and requires a noise gain of ≥3 for unconditional stability. It is not unity-gain stable. Attempting G = 1 or G = 2 without external compensation will cause oscillation or severe peaking. Verified stability data confirms stable operation at G = +3, +5, +10, and +20 with appropriate layout and decoupling. Always refer to Figure 5 and Figure 6 in the official OPA643 datasheet for low-gain compensation networks when using OPA643N/3K.

Does OPA643N/3K support single-supply operation?

No - the OPA643N/3K is specified and characterized for dual-supply operation only (±4.5V to ±5.5V). Its input common-mode range is centered at ground (±2.75V), and output swing is symmetrical about 0V. While rail-to-rail input/output is not supported, the device can be biased for pseudo-single-supply use with external level-shifting networks, but such configurations are not tested or guaranteed by TI. For true single-supply designs, consider alternatives like OPA837 or THS3491.

What is the thermal resistance (θ_JA) of the OPA643N/3K package?

The OPA643N/3K in SOT23-5 package has a junction-to-ambient thermal resistance (θ_JA) of 150°C/W under standard JEDEC test conditions (1s² copper pad, no airflow). This value assumes minimal PCB copper; adding thermal vias and 1-in² copper pour reduces effective θ_JA to ~65°C/W. At 25mA quiescent current and ±5V supplies, power dissipation is ~250mW - resulting in ~37.5°C junction rise above ambient in standard layout, well within the +175°C max rating.

Can OPA643N/3K drive a 50Ω load directly?

Yes - the OPA643N/3K delivers ±60mA output current and is fully specified into 100Ω loads. Driving a 50Ω load is feasible: at ±2.75V output swing (typical into 100Ω), it delivers ±27.5mA - well within its ±60mA capability. However, power dissipation increases (to ~300mW at full swing), requiring attention to thermal layout. The datasheet confirms stable operation with 50Ω series termination (Figure 1), confirming OPA643N/3K suitability for 50Ω IF/video line driving.

How does OPA643N/3K differ from OPA643U or OPA643P?

The OPA643N/3K shares identical electrical specifications with OPA643U (SO-8) and OPA643P (DIP), but differs in package: SOT23-5 vs. SO-8 vs. 8-pin DIP. Key distinctions include θ_JA (150°C/W vs. 125°C/W vs. 100°C/W), pin count (5 vs. 8), and distortion performance - the SOT23-5's shorter bond wires yield ~4dB better 5MHz 2nd-harmonic distortion than SO-8. All variants require same external compensation for low-gain use and share identical gain-stability requirements.