Texas Instruments SN74LVC646ADWG4

Overview

SN74LVC646ADWG4 from Texas Instruments is an octal bus transceiver and register with 3-state outputs, designed for 1.65 V to 3.6 V operation. It integrates dual 8-bit registers, clocked A↔B bidirectional data transfer, direction control (DIR), output enable (OE), and select controls (SAB/SBA) - enabling real-time or stored-data routing in mixed-voltage systems. It supports 5.5 V-tolerant inputs and delivers 7.4 ns max propagation delay at 3.3 V in high-speed bus isolation applications.

For engineers reviewing the SN74LVC646ADWG4 datasheet, SN74LVC646ADWG4 pinout, SN74LVC646ADWG4 application, or SN74LVC646ADWG4 equivalent, key selection criteria include its dual-register architecture, Ioff partial-power-down support, 3.3 V/5 V mixed-mode signal compatibility, and TSSOP-24 package constraints - all critical for legacy-to-modern voltage interface design and synchronous bus buffering.

Technical Context

The SN74LVC646ADWG4 implements two independent 8-bit D-type flip-flop registers clocked on rising edges of CLKAB (A→B) and CLKBA (B→A), allowing concurrent storage of data from either bus. Its transceiver logic uses DIR to determine data flow direction and OE to place outputs in high-impedance state - supporting both transparent and registered modes via SAB/SBA select inputs.

It features Ioff circuitry that disables outputs during power-down to prevent backflow current, and accepts input voltages up to 5.5 V regardless of VCC (1.65–3.6 V), enabling safe interfacing between 3.3 V logic and 5 V peripherals. The device meets JESD 17 latch-up >250 mA and exceeds JESD 22 ESD ratings (2000-V HBM, 200-V MM, 1000-V CDM).

Key Specifications

Pinout & Package

TSSOP-24 package (PW), 7.8 mm × 4.4 mm × 1.2 mm max height, 0.65 mm lead pitch, gull-wing leads, RoHS-compliant NiPdAu finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal registered transceiver applications.

Compared with SN74LVC646ADBR (SSOP) and SN74LVC646APWR (TSSOP), SN74LVC646ADWG4 provides identical logic functionality and timing but with TI's G4-enhanced surface finish - offering superior wetting performance in lead-free reflow profiles without altering thermal or electrical behavior.

Availability

SN74LVC646ADWG4 is available at Aetrix Electronics and suitable for industrial automation interfaces, automotive body electronics, embedded test equipment, and FPGA-to-MCU bridging applications requiring stable component supply across extended product lifecycles.

Supply support for SN74LVC646ADWG4 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 connectivity technologies, with over 50 years of innovation in logic, power management, and signal chain solutions.

The SN74LVC646ADWG4 belongs to TI's LVC (Low-Voltage CMOS) logic family, engineered for high-speed, low-power, mixed-voltage bus interfacing in industrial, automotive, and communications systems.

FAQ

What is the maximum clock frequency supported by SN74LVC646ADWG4?

The SN74LVC646ADWG4 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). At lower VCC (e.g., 1.8 V), maximum frequency is not characterized per the datasheet, so 150 MHz is guaranteed only at 2.7–3.6 V operation.

Does SN74LVC646ADWG4 support true 5 V to 3.3 V level translation?

Yes, SN74LVC646ADWG4 supports true bidirectional level translation: its inputs tolerate up to 5.5 V regardless of VCC (1.65–3.6 V), and outputs swing rail-to-rail within the VCC range. When VCC = 3.3 V, it safely accepts 5 V inputs and drives 3.3 V-compatible loads - no external resistors or translators needed for A/B bus interfacing.

What is the purpose of the SAB and SBA pins on SN74LVC646ADWG4?

SAB (Select A to B) and SBA (Select B to A) control whether real-time or registered data appears on the output bus. When DIR = H and OE = L, SAB = H selects stored A data for output to B; when DIR = L and OE = L, SBA = H selects stored B data for output to A. These pins enable flexible multiplexing between live and latched data paths without additional logic.

Can SN74LVC646ADWG4 operate with VCC = 1.8 V, and what are the implications?

Yes, SN74LVC646ADWG4 is fully specified from 1.65 V to 3.6 V. At VCC = 1.8 V, output drive strength reduces (IOL = 4 mA, IOH = –4 mA), propagation delay increases (tpd not characterized below 2.7 V), and VIH/VIL thresholds scale proportionally (VIH = 0.65 × VCC ≈ 1.17 V). System timing margins must be re-verified per actual load and trace conditions.

How does the Ioff feature function in SN74LVC646ADWG4 during power-down?

The Ioff circuitry in SN74LVC646ADWG4 automatically disables all outputs when VCC = 0 V, preventing current backflow from live buses (e.g., 5 V A or B lines) into the unpowered device. This eliminates risk of latch-up or damage in partial-power-down systems - no external isolation components are required, simplifying power sequencing in multi-rail designs.