Texas Instruments OPA861ID

Overview

OPA861ID from Texas Instruments is a wideband bipolar operational transconductance amplifier (OTA) with 80MHz open-loop bandwidth (G = +5), 900V/µs slew rate, 95mA/V transconductance, ±5V supply operation, and SO-8 package. It serves as a voltage-controlled current source in high-speed video, RF, and active filter circuits where precise transconductance control and low quiescent current (5.4mA) are critical.

For engineers reviewing the OPA861ID datasheet, OPA861ID pinout, OPA861ID application, or OPA861ID equivalent, this page delivers verified specifications, SO-8 terminal mapping, real-world use cases in broadcast equipment and wideband LED drivers, and two validated alternative OTAs for bandwidth-sensitive analog signal paths.

Technical Context

The OPA861ID implements a three-terminal OTA architecture with high-impedance B-input (base), low-impedance E-input/output (emitter), and high-impedance C-output (collector), enabling transistor-like circuit topologies without external biasing. Its transconductance is externally adjustable via an IQ-adjust resistor (250Ω typical), directly tuning bandwidth, gain, and quiescent current trade-offs.

It operates over –45°C to +85°C with ±5V supply, supports rail-to-rail input common-mode range (±VS), delivers ±15mA E/C output current, and maintains stable transconductance across temperature due to self-biasing-unlike discrete transistors whose gm drifts significantly.

Key Specifications

Pinout & Package

OPA861ID is housed in an SO-8 surface-mount package (package code D), with thermal resistance θ_JA = 125°C/W. Pin functions are validated per TI SBOS338G Rev. May 2013.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LMH6552MA and OPA684ID, the OPA861ID uniquely balances 80MHz bandwidth, 5.4mA quiescent current, and external gm control-making it optimal for power-constrained, tunable active filters and video line drivers where transistor-like circuit intuition applies.

Availability

OPA861ID is available at Aetrix Electronics and suitable for video/broadcast equipment, high-speed data acquisition, and wideband LED drivers requiring stable component supply across extended temperature ranges (–45°C to +85°C).

Supply support for OPA861ID 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 is a global semiconductor leader delivering analog, embedded processing, and logic solutions with emphasis on high-reliability, high-performance signal chain products.

The OPA861ID belongs to TI's high-speed operational transconductance amplifier product line, designed specifically for wideband analog signal processing in video, RF, and precision instrumentation where gm tunability and low-noise operation are essential.

FAQ

What is the primary function of the OPA861ID in circuit design?

The OPA861ID functions as a voltage-controlled current source (operational transconductance amplifier) with three terminals-B (high-Z input), E (low-Z I/O), and C (high-Z current output). Its core role is to convert a differential voltage at the B–E junction into a proportional output current at the C terminal, enabling transistor-like analog computation, active filtering, and high-speed amplification without external biasing networks. This behavior is explicitly defined in TI SBOS338G Section 1.1 and Figure 29.

How does the IQ Adjust pin (Pin 1) affect OPA861ID performance?

The IQ Adjust pin on the OPA861ID sets total quiescent current by connecting an external resistor (250Ω typical) between Pin 1 and V−. This directly controls transconductance (gm), bandwidth, slew rate, and harmonic distortion: lowering RADJ increases IQ, raising gm from ~37mA/V to 160mA/V and bandwidth from 70MHz to 80MHz. TI SBOS338G Figure 12 and Section 8.2.2 confirm this linear relationship and its impact on AC performance.

Can the OPA861ID operate from a single +5V supply?

Yes, the OPA861ID supports single +5V operation per Electrical Characteristics table on page 4 of SBOS338G. In this mode, the specified operating voltage is 5V, maximum is 12.6V, and minimum is 4V. Input common-mode range extends from 0.8V to 4.2V, and E/C output compliance is 0.8V to 4.2V (sourcing) and 0.3V to 3.9V (sinking), enabling rail-aware designs such as LED drivers and DC-restored video circuits.

What is the significance of the NC pins (Pins 5 and 6) on the OPA861ID SO-8 package?

Pins 5 and 6 on the OPA861ID SO-8 package are designated No Connect (NC) with no internal electrical connection, as confirmed in TI SBOS338G Figure 1 (Pin Configuration) and Table 1 (Ordering Information). These pins must remain unconnected in PCB layout; routing traces or applying solder paste to them risks shorting adjacent pins or violating thermal/mechanical reliability requirements defined in TI's SO-8 packaging guidelines.

How does the OPA861ID compare to a discrete NPN transistor in common-emitter configuration?

Unlike a discrete NPN transistor, the OPA861ID provides self-biasing (no base resistors needed), constant transconductance over temperature, ±3mV input offset (vs. volts of V_BE drift), and symmetrical sourcing/sinking current at both E and C terminals. TI SBOS338G Figure 32 explicitly contrasts these behaviors, showing OPA861ID achieves 0V output offset and stable gm while eliminating thermal runaway and bias network complexity inherent in discrete implementations.