Texas Instruments OPA3S2859IRTWR

Overview

OPA3S2859 from Texas Instruments is a dual-channel, 900-MHz gain-bandwidth programmable transimpedance amplifier (TIA) with FET inputs, 2.2-nV/√Hz input voltage noise, and internal switched feedback paths for gain selection across three ranges (<1 kΩ, 10 kΩ, 100 kΩ). It operates from 3.3 V to 5.25 V and supports laser distance measurement and SiPM buffering.

For engineers reviewing the OPA3S2859 datasheet, OPA3S2859 pinout, OPA3S2859 application, or OPA3S2859 equivalent, this page delivers verified technical context, real-world design meaning of key specs, validated pin functions, confirmed application use cases, and two rigorously cross-checked alternative parts - all grounded in TI's SBOSA13A production data sheet.

Technical Context

The OPA3S2859 integrates two independent high-speed TIA channels, each with three internal CMOS switches on both COM and FB paths to select gain configurations. Its 900-MHz GBWP enables >130 MHz closed-loop bandwidth at 1-kΩ gain with 4-pF photodiode capacitance.

Gain selection uses a 2-wire parallel interface (SEL0/SEL1) with latch control (LTCH_A/LTCH_B) per channel to hold gain state. Power-down mode reduces quiescent current to 75 µA per channel while maintaining switch state integrity.

Key Specifications

Pinout & Package

OPA3S2859 is housed in a 24-pin WQFN package (4.00 mm × 4.00 mm) with exposed thermal pad connected to VS−. The layout supports dual independent TIAs with dedicated COM, FB, and latch pins per channel.

Key Features

Applications

Equivalent & Alternatives

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

Compared with OPA657IDBVR and LMH6629MA/NOPB, the OPA3S2859 uniquely delivers dual-channel programmable-gain TIA functionality in one package - eliminating board-level muxes, reducing layout sensitivity, and enabling synchronized gain switching across channels without added latency or skew.

Availability

OPA3S2859 is available at Aetrix Electronics and suitable for laser rangefinding, optical time-domain reflectometry, and silicon photomultiplier buffering requiring stable component supply across industrial, defense, and test equipment programs.

Supply support for OPA3S2859 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 specializing in analog and embedded processing technologies, with decades of expertise in high-speed amplifiers and precision signal chain solutions.

The OPA3S2859 belongs to TI's high-performance transimpedance amplifier product line, designed specifically for optical sensing applications demanding wide bandwidth, low noise, and flexible gain configuration in compact form factors.

FAQ

What is the primary function of the OPA3S2859?

The OPA3S2859 is a dual-channel programmable-gain transimpedance amplifier optimized for converting photodiode current into voltage with high bandwidth and low noise. Its internal switched feedback paths enable rapid gain reconfiguration without external components - making it ideal for laser distance measurement, OTDR, and SiPM readout where signal dynamics vary across measurement conditions. Each channel of the OPA3S2859 operates independently with dedicated latch and selection controls.

How does the OPA3S2859 achieve different gain settings?

The OPA3S2859 uses three internal CMOS switches per channel - two per gain path (COM-side and FB-side) - to connect discrete external feedback resistors to the inverting input. SEL0 and SEL1 pins decode into four gain states: three internal (low/mid/high) and one external (all switches open). The OPA3S2859's switch R_ON (35–375 Ω) and C_OFF (<1.4 pF) are characterized to minimize parasitic impact on bandwidth and stability - unlike discrete mux solutions that introduce unpredictable capacitance and resistance.

What is the significance of the LTCH_A and LTCH_B pins on the OPA3S2859?

LTCH_A and LTCH_B are per-channel latch enable inputs that freeze the currently selected gain configuration. When pulled low, they decouple the amplifier from SEL0/SEL1 control - preventing gain changes during noisy digital transitions or critical acquisition windows. This feature is essential in synchronized dual-channel systems like differential OTDR or time-of-flight sensors where gain mismatch between channels would corrupt measurement accuracy. The OPA3S2859 maintains latched state even during brief supply fluctuations.

Can the OPA3S2859 operate from a single 3.3-V supply?

Yes, the OPA3S2859 supports single-supply operation from 3.3 V to 5.25 V. Its input common-mode range extends from 0 V to 1.9 V (at 3.3-V supply) with CMRR >64 dB, and output swing reaches 1.05–2.4 V depending on load. Internal biasing allows midsupply referencing for photodiode connections, and the device maintains full AC performance - including 130 MHz bandwidth at 1-kΩ gain - under 3.3-V operation. Quiescent current remains within spec (39–51 mA total) across the full temperature range.

What thermal considerations apply to the OPA3S2859 package?

The OPA3S2859 uses a 24-pin WQFN (RTW) package with an exposed thermal pad that must be soldered to a VS− copper plane. Its junction-to-board thermal resistance is 28.2 °C/W, and junction-to-ambient is 52 °C/W - meaning proper PCB thermal design is essential for sustained operation at 125°C ambient. At 44 mA total quiescent current and 5-V supply, power dissipation is ~220 mW; without adequate copper area, junction temperature can exceed 150°C. TI recommends minimum 250 mm² thermal pad area with ≥4 thermal vias to inner ground planes.