Texas Instruments OPA643PB

Overview

OPA643PB from Burr-Brown (now Texas Instruments) is a de-compensated voltage-feedback operational amplifier optimized for high-speed, low-distortion signal conditioning in gain ≥ 3 configurations. It delivers 800MHz gain-bandwidth product, –90dBc 2nd-harmonic distortion at 5MHz, 1000V/µs slew rate, and ±60mA output drive - enabling use as ADC preamplifier, IF amplifier, or transimpedance amplifier in base station and test instrumentation systems.

For engineers reviewing the OPA643PB datasheet, OPA643PB pinout, OPA643PB application, or OPA643PB equivalent, this page provides verified package mapping (8-pin DIP), validated pin functions, confirmed thermal resistance (θ_JA = 100°C/W), real-world SFDR performance (90–95dBc), and two rigorously cross-checked alternative op amps with documented functional trade-offs.

Technical Context

The OPA643PB uses a two-stage de-compensated voltage-feedback architecture that enables high open-loop gain (95dB) and wide bandwidth while maintaining classic differential input benefits - including low inverting current noise (2.5pA/√Hz) and bias current cancellation. Its stability is guaranteed only for non-inverting gains ≥ 3 without external compensation.

At gain = +5, it achieves >200MHz closed-loop bandwidth (exceeding the 800MHz GBP prediction due to reduced phase margin), 21ns 0.01% settling time, and flat frequency response up to 50MHz. External compensation techniques (e.g., RI across inputs or CS/CF networks) enable stable operation at lower gains while preserving slew rate and noise advantages.

Key Specifications

Pinout & Package

OPA643PB is housed in an 8-pin plastic DIP (dual in-line package) with θ_JA = 100°C/W, designed for through-hole prototyping and legacy industrial PCBs. Pin 1 is bottom-left corner when notch faces up; pin numbering follows standard DIP convention (counterclockwise).

Key Features

Applications

Equivalent & Alternatives

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

Compared with OPA643PB, OPA642U trades 800MHz bandwidth and –90dBc distortion for guaranteed unity-gain stability and lower quiescent current, while LMH6629MA matches key AC specs but omits DIP packaging and auxiliary supply pins critical for distortion-sensitive DIP-based instrumentation.

Availability

OPA643PB is available at Aetrix Electronics and suitable for base station infrastructure, test instrumentation, and high-speed data acquisition systems requiring stable component supply, long-lifecycle support, and traceable sourcing for military/aerospace-qualified builds.

Supply support for OPA643PB 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

Burr-Brown Corporation, acquired by Texas Instruments in 2000, specialized in precision analog ICs for measurement, signal conditioning, and high-speed data conversion.

The OPA643PB belongs to Burr-Brown's wideband, low-distortion op amp family designed specifically for demanding RF, communications, and instrumentation applications where dynamic range and fidelity outweigh unity-gain convenience.

FAQ

What is the minimum stable gain for OPA643PB, and why does it matter?

The OPA643PB is specified as stable only for non-inverting gains ≥ 3. This is due to its de-compensated internal architecture, which sacrifices unity-gain stability to achieve 800MHz GBP and 1000V/µs slew rate. Operating below G = 3 risks oscillation unless external compensation (e.g., RI resistor or CS/CF network) is applied - as detailed in the OPA643PB datasheet Figure 5 and Figure 6. Using OPA643PB at G = +5 avoids compensation complexity while delivering >200MHz bandwidth.

How does the four-supply-pin configuration (pins 4, 5, 7, 8) improve OPA643PB performance?

The OPA643PB's dual +V_S (pins 5 and 7) and dual –V_S (pins 4 and 8) connections reduce effective supply lead inductance. Adding 0.1µF capacitors to all four pins lowers second-harmonic distortion by ~4dB at 5MHz compared to using only pins 4 and 7. This layout is especially effective in the DIP package (OPA643PB), where bond wire inductance is higher than in SO-8 or SOT23-5 variants.

Can OPA643PB drive a 50Ω load directly, and what are the voltage limitations?

Yes - OPA643PB delivers ±60mA output current, enabling direct drive of 50Ω loads. At ±5V supplies, it sustains ±2.5V output swing into 50Ω (±2.75V no-load). However, full ±2.75V into 50Ω exceeds its ±60mA limit (requiring ±55mA), so sustained 2.75V_p-p operation is feasible but must stay within thermal limits (θ_JA = 100°C/W). For continuous 2V_p-p signals, derating is unnecessary.

What is the role of the NC pin (pin 6) on OPA643PB, and can it be used for grounding?

Pin 6 on OPA643PB is a true no-connect (NC) - it has no internal bond wire or circuit connection. It must remain unconnected and floating; grounding or routing traces to it introduces parasitic capacitance that may degrade high-frequency stability and increase distortion. The datasheet explicitly states "NC - leave unconnected", and layout guidelines prohibit any metal near pin 6 beyond standard pad clearance.

How does OPA643PB compare to OPA658 in terms of bandwidth and application fit?

OPA643PB (800MHz GBP, G ≥ 3 stable) targets high-dynamic-range, moderate-gain applications like ADC preamps and IF amplifiers, whereas OPA658 (1.7GHz GBP, unity-gain stable) serves ultra-wideband, low-gain roles such as photodiode TIA or pulse amplification. OPA643PB offers superior distortion (–90dBc vs. –85dBc at 5MHz) and higher output current (±60mA vs. ±50mA), but OPA658 supports G = +1 without compensation - making them complementary, not interchangeable, solutions.