Texas Instruments SN74LVT646DW

Overview

SN74LVT646DW from Texas Instruments is a 3.3-V ABT octal bus transceiver and register with 3-state outputs, designed for mixed-mode signal operation between 3.3-V and 5-V systems. It features dual 8-bit buses (A and B), clocked D-type flip-flops, direction control (DIR), output enable (OE), and select controls (SAB/SBA) for real-time or registered data transfer. It supports live insertion and bus-hold inputs, and operates from –40°C to 85°C in a 24-pin SOIC (DW) package.

For engineers reviewing the SN74LVT646DW datasheet, SN74LVT646DW pinout, SN74LVT646DW application, or SN74LVT646DW equivalent, key selection criteria include 3.3-V VCC compatibility with 5-V tolerant I/O, octal bidirectional data flow with register storage, 150-MHz clock frequency support, 3-state output control timing (tPZH/tPLZ < 7.5 ns), and SOIC-24 thermal performance (1.7 W max at 55°C).

Technical Context

The SN74LVT646DW implements an Advanced BiCMOS Technology (ABT) architecture enabling low static power dissipation while supporting TTL-level interfacing at 3.3-V supply. Its dual-clock system (CLKAB/CLKBA) allows independent latching of A- or B-bus data on rising edges, with DIR selecting transmission direction and OE enabling/disabling outputs.

Bus-hold circuitry maintains valid logic levels on unused inputs without external pullups. The device supports isolation mode (OE high) for concurrent storage of A and B data, and transparent or registered transfer modes controlled by SAB/SBA-enabling flexible bus management in backplane, memory interface, and protocol bridge applications.

Key Specifications

Pinout & Package

The SN74LVT646DW is housed in a 24-pin plastic small-outline integrated circuit (SOIC) package (DW), 7.50 mm × 15.40 mm body size, with 1.27 mm lead pitch and gull-wing leads. Pin numbering follows standard JEDEC SOIC top-view convention.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal bus transceiver and register applications.

Compared with SN74LVT646DW, SN74LVTH16646DLR offers double the data width but sacrifices 5-V I/O compatibility and registered transfer flexibility, while 74ALVC164245DGGR provides scalable voltage translation but lacks internal registers and dual-clock control-making SN74LVT646DW uniquely suited for synchronous, mixed-voltage bus management with storage.

Availability

SN74LVT646DW is available at Aetrix Electronics and suitable for industrial control backplanes, memory interface bridging, protocol translation modules, and modular computing chassis requiring stable component supply across extended temperature ranges.

Supply support for SN74LVT646DW 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 company headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, and communications markets.

The SN74LVT646DW belongs to TI's ABT logic family, engineered for high-speed, low-power 3.3-V bus interfacing with backward compatibility to 5-V systems-targeting applications where signal integrity, voltage translation, and synchronous data registration are critical.

FAQ

What is the maximum clock frequency supported by the SN74LVT646DW?

The SN74LVT646DW supports a maximum clock frequency of 150 MHz across its recommended operating range (VCC = 2.7 V to 3.6 V, TA = –40°C to 85°C). This specification is validated under CL = 50 pF load conditions and applies to both CLKAB and CLKBA inputs. Timing parameters such as t_su, t_h, and propagation delays remain within datasheet limits up to this rate, making SN74LVT646DW suitable for high-throughput data routing in telecom and computing infrastructure.

Does the SN74LVT646DW require external pullup resistors on its data inputs?

No, the SN74LVT646DW does not require external pullup resistors on its A1–A8 or B1–B8 data inputs due to integrated bus-hold circuitry. This feature actively maintains a valid logic level (VIH ≥ 2 V or VIL ≤ 0.8 V) on floating inputs with ±75 µA hold current. External pullups are unnecessary unless specific system-level noise immunity requirements exceed the built-in bus-hold strength, in which case 10-kΩ resistors may be added-but SN74LVT646DW functionality remains fully operational without them.

Can the SN74LVT646DW operate with a 2.5-V supply voltage?

No, the SN74LVT646DW is not rated for reliable operation at 2.5 V. Its recommended operating VCC range is strictly 2.7 V to 3.6 V, with absolute maximum ratings extending only to –0.5 V and 4.6 V. At 2.5 V, parameters including VOL, VOH, t_PLH/t_PHL, and bus-hold functionality fall outside guaranteed specifications. For 2.5-V systems, consider TI's ALVC or LVC families instead-SN74LVT646DW must be used within its defined 2.7–3.6 V window to ensure compliance with timing, drive strength, and noise margin specs.

How does the SN74LVT646DW handle power-up sequencing when OE is not externally controlled?

To ensure high-impedance outputs during power-up, OE on the SN74LVT646DW should be tied to VCC through a pullup resistor; TI recommends a minimum value determined by the driver's current-sinking capability (typically ≤10 kΩ). Without this, OE may float, causing undefined output states and potential bus contention. The SN74LVT646DW itself has no internal power-on reset-external OE control or pullup is mandatory for robust startup behavior in systems with asynchronous power rails.

Is the SN74LVT646DW pin-compatible with the SN74LVT640 or SN74LVT645?

No, the SN74LVT646DW is not pin-compatible with SN74LVT640 or SN74LVT645. While all three are octal transceivers in DW packages, SN74LVT640 lacks registers and clock inputs (CLKAB/CLKBA), and SN74LVT645 omits SAB/SBA select controls and uses different pin assignments for DIR and OE. The SN74LVT646DW's 24-pin SOIC layout-including dedicated CLKAB (pin 1), CLKBA (pin 23), SAB (pin 2), and SBA (pin 22)-is unique to its registered transceiver function and cannot be substituted without PCB redesign.