Texas Instruments SN74LVC646DW

Overview

SN74LVC646DW from Texas Instruments is an octal bus transceiver and register with 3-state outputs, designed for bidirectional data flow control between two 8-bit buses (A and B) in mixed-voltage systems. It operates from 1.65 V to 3.6 V, supports 5.5-V-tolerant inputs, features Ioff partial-power-down protection, and delivers 7.4 ns max propagation delay at 3.3 V - enabling use in high-speed logic interfacing, memory expansion, and FPGA-to-ASIC data bridging.

For engineers reviewing the SN74LVC646DW datasheet, SN74LVC646DW pinout, SN74LVC646DW application, or SN74LVC646DW equivalent, key selection criteria include its dual-clock register architecture (CLKAB/CLKBA), direction-controlled real-time or stored-data transfer modes, 24-pin SOIC-DW package compatibility, and support for 3.3-V/5-V mixed-signal translation without level shifters.

Technical Context

The SN74LVC646DW integrates eight independent bidirectional channels, each with D-type flip-flop storage, clocked on low-to-high transitions of CLKAB (A→B) or CLKBA (B→A). Its control logic combines OE (output enable), DIR (direction), and SAB/SBA (select) inputs to configure four distinct bus-management functions: real-time transfer, stored-data transfer, isolation with concurrent A/B storage, and register-only capture.

It implements Ioff circuitry to disable outputs during power-down, preventing backflow current when VCC = 0 V while inputs remain at up to 5.5 V. Input thresholds scale with VCC (VIH = 0.65×VCC min at 1.65 V), and output drive strength scales with supply voltage (IOL = 24 mA at VCC = 3.0 V), ensuring robust operation across its full 1.65–3.6 V range.

Key Specifications

Pinout & Package

SN74LVC646DW uses a 24-pin SOIC (DW) package with 0.300-inch body width and standard JEDEC MO-058 compliance. Pin numbering follows top-view orientation with Pin 1 at bottom-left corner.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVC646ADBR and SN74LVC646APWR, the SN74LVC646DW offers superior manufacturability in standard through-hole-compatible SOIC assembly lines, better thermal dissipation (θJA = 46°C/W), and wider availability in tube packaging for prototyping - making it the preferred choice for industrial control and test equipment development.

Availability

SN74LVC646DW is available at Aetrix Electronics and suitable for industrial PLC backplanes, FPGA-to-MCU bridging, and memory expansion interfaces requiring stable component supply, long-term lifecycle support, and RoHS-compliant green packaging.

Supply support for SN74LVC646DW 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, embedded processing, and logic solutions, with decades of expertise in high-reliability interface ICs.

The SN74LVC646DW belongs to TI's LVC logic family, engineered for low-voltage, high-speed bidirectional bus management in mixed-signal systems - targeting industrial automation, test instrumentation, and programmable logic interconnect applications.

FAQ

What is the maximum clock frequency supported by SN74LVC646DW?

The SN74LVC646DW supports a maximum clock frequency of 150 MHz at VCC = 3.3 V, as specified in the timing requirements table. This applies to both CLKAB and CLKBA inputs under recommended operating conditions (TA = –40°C to +85°C, VCC = 2.7 V to 3.6 V). At lower VCC values (e.g., 1.8 V), published timing data is not available, so design margins must be verified empirically.

Does SN74LVC646DW support true 5-V to 3.3-V level translation?

Yes, SN74LVC646DW supports 5-V-tolerant inputs (up to 5.5 V) while operating from a 1.65–3.6-V VCC supply, enabling direct connection to 5-V logic without external level shifters. However, its outputs swing only to VCC levels (e.g., 3.3 V max), so downstream 5-V receivers require input threshold compatibility - confirmed by VIH(min) = 2.0 V at VCC = 3.3 V.

How does the Ioff feature protect SN74LVC646DW during partial power-down?

The Ioff circuitry in SN74LVC646DW disables all outputs when VCC = 0 V, regardless of input voltage (up to 5.5 V), preventing reverse current flow from powered buses into the unpowered device. This protects against latch-up and ensures safe hot-swap operation in modular systems - a requirement explicitly tested per JESD 78.

Can SN74LVC646DW operate with only one bus active while the other is held static?

Yes. In isolation mode (OE = high), SN74LVC646DW stores data independently on both A and B buses. When OE is low, DIR selects direction and SAB/SBA selects source (real-time or stored), allowing one bus to remain static while the other transfers data - ideal for handshake protocols and buffered peripheral interfacing.

What is the thermal resistance (θJA) of the SN74LVC646DW package?

The SN74LVC646DW in SOIC-DW package has a junction-to-ambient thermal resistance (θJA) of 46°C/W, measured per JESD 51-7 on a standard 4-layer JEDEC test board. This value assumes no copper pour or thermal vias; actual board-level θJA will improve with proper thermal land design and airflow.