Texas Instruments OPA643P

Overview

OPA643P from Burr-Brown (now Texas Instruments) is a decompensated voltage-feedback operational amplifier optimized for high-speed, low-distortion signal conditioning in gain ≥ 3 configurations. It delivers 800MHz gain-bandwidth product, 1000V/µs slew rate, –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 base station and test instrumentation systems.

For engineers reviewing the OPA643P datasheet, OPA643P pinout, OPA643P application, or OPA643P equivalent, this page provides verified package mapping (8-pin PDIP), 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 OPA643P uses a two-stage decompensated voltage-feedback architecture that achieves high open-loop gain (95dB) and wide bandwidth while maintaining classic differential input benefits - including low inverting current noise and bias current cancellation. Its stability is guaranteed only for non-inverting gains ≥ 3, requiring external compensation for unity- or low-gain operation.

Performance is highly dependent on power supply decoupling: pins 4 (–VS) and 7 (+VS) are primary supply connections, but optimal distortion requires additional 0.1µF capacitors on pins 5 and 8 (internally tied to pins 4 and 7) to suppress lead inductance effects - a layout requirement explicitly validated for the P/PB DIP package.

Key Specifications

Pinout & Package

OPA643P is housed in an 8-pin plastic dual in-line package (PDIP) with θ_JA = 100°C/W. Pin 1 is bottom-left corner (notch-down orientation); pin numbering follows standard DIP convention (counterclockwise from notch).

Key Features

Applications

Equivalent & Alternatives

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

Compared with OPA643P, OPA642U sacrifices bandwidth and noise performance for inherent stability, while LMH6629MA offers higher slew rate but demands board revision and lacks the four-supply-pin architecture critical for low-distortion DIP implementations.

Availability

OPA643P is available at Aetrix Electronics and suitable for base station RF front-ends, high-fidelity video signal distribution, and automated test equipment requiring stable component supply across extended temperature ranges (–40°C to +85°C).

Supply support for OPA643P 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 with emphasis on high-speed, low-noise, and high-dynamic-range signal conditioning.

The OPA643P belongs to Burr-Brown's OPA6xx high-speed op amp family, designed specifically for demanding communications and instrumentation applications where distortion, noise, and bandwidth must be simultaneously optimized.

FAQ

What is the minimum stable gain for the OPA643P, and why is it specified?

The OPA643P is decompensated and guaranteed stable only for non-inverting gains ≥ +3. This design choice maximizes gain-bandwidth product (800MHz) and slew rate (1000V/µs) by reducing internal compensation capacitance. Operating below G = +3 risks oscillation unless external compensation (e.g., RI resistor or CF/CS network) is applied - as detailed in Figures 5 and 6 of the OPA643P datasheet. Stability verification is mandatory for any G < +3 implementation.

Does the OPA643P require special power supply decoupling beyond standard practices?

Yes. The OPA643P's 8-pin DIP package (P/PB variants) requires decoupling on all four supply pins: pins 4 (–VS), 5 (+VS2), 7 (+VS), and 8 (–VS2). Although pins 5 and 8 are internally tied to 7 and 4 respectively, adding 0.1µF capacitors to pins 5 and 8 reduces supply lead inductance and improves second-harmonic distortion by ~4dB at 5MHz - a requirement explicitly validated in the OPA643P datasheet's Applications Information section.

Can the OPA643P drive a 50Ω load directly, and what are the implications?

The OPA643P can drive a 50Ω load, but output voltage swing is reduced: ±2.5V maximum at temperature extremes, ±2.75V at +25°C. Driving 50Ω continuously draws up to ±60mA, increasing junction temperature and potentially triggering thermal shutdown if ambient exceeds +75°C. For sustained 50Ω operation, derate power dissipation using θ_JA = 100°C/W and ensure adequate airflow - the OPA643P datasheet specifies ±40mA typical output into 100Ω, not 50Ω.

How does the OPA643P's distortion performance compare at different output voltage swings?

OPA643P distortion degrades with increasing output swing: at 5MHz, 2nd-harmonic distortion is –90dBc at 1V_p-p, –85dBc at 2V_p-p, and –75dBc at 4V_p-p. This trend is confirmed in Figure 4 of the OPA643P datasheet. For SFDR-critical applications (e.g., ADC preamps), operating at ≤2V_p-p preserves >90dBc performance - essential for maintaining 12-bit+ ENOB in high-dynamic-range digitizers.

Is the OPA643P suitable for transimpedance amplifier applications, and what compensation is needed?

Yes - the OPA643P is well-suited for wideband transimpedance amplifiers due to its 800MHz GBP, low input voltage noise (2.3nV/√Hz), and low input current noise (2.5pA/√Hz). Compensation requires calculating feedback capacitance CF based on photodiode capacitance CD, OPA643P's input capacitance (3.8pF total), and target bandwidth. For example, with CD = 20pF and RF = 10kΩ, CF = 0.8pF yields ~23MHz Butterworth response - values validated in Figure 3 of the OPA643P datasheet.