Texas Instruments SN74LVTH646PW

Overview

SN74LVTH646PW from Texas Instruments is a 3.3-V octal bus transceiver with registers, dual-clock control (CLKAB/CLKBA), direction control (DIR), and output enable (OE), supporting mixed-mode 5-V/3.3-V interfacing in backplane or motherboard data routing applications.

For engineers reviewing the SN74LVTH646PW datasheet, SN74LVTH646PW pinout, SN74LVTH646PW application, or SN74LVTH646PW equivalent, key selection criteria include its 24-pin TSSOP package, bus-hold inputs eliminating external resistors, Ioff hot-insertion support, 150-MHz clock frequency capability, and dual-register storage for A/B bus isolation and multiplexed transfer.

Technical Context

The SN74LVTH646PW integrates eight bidirectional data channels with independent D-type flip-flop registers on both A and B buses, controlled by two asynchronous clocks (CLKAB and CLKBA) and select lines (SAB/SBA). It supports real-time transparent transfer and stored-data forwarding under DIR and OE logic control.

Its architecture enables four core bus-management functions: real-time A→B or B→A transfer, simultaneous A+B storage, and isolated register hold mode - all while maintaining 3.3-V VCC operation with 5-V tolerant inputs and outputs. Bus-hold circuitry actively maintains valid logic states on floating A/B inputs without external components.

Key Specifications

Pinout & Package

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

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVCZ16245A and SN74ALVCH162245, the SN74LVTH646PW uniquely combines 5-V-tolerant I/O, dual-clock register staging, bus-hold, and SAB/SBA multiplexing - making it irreplaceable for mixed-voltage bus arbitration requiring temporal decoupling and flexible data path control.

Availability

SN74LVTH646PW is available at Aetrix Electronics and suitable for industrial PLC I/O modules, test equipment signal switching, and memory-mapped peripheral bridge designs requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant TSSOP packaging.

Supply support for SN74LVTH646PW 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 over 50 years of innovation in industrial, automotive, and communications infrastructure markets.

The SN74LVTH646PW belongs to TI's LVTH logic family, engineered for mixed-voltage system interfacing where 3.3-V core logic must reliably communicate with legacy 5-V buses without external level-shifting circuitry.

FAQ

What voltage levels does the SN74LVTH646PW support on its I/O pins?

The SN74LVTH646PW supports 5-V-tolerant inputs and outputs while operating from a 3.3-V VCC supply. Its input voltage range extends to 5.5 V, allowing direct connection to 5-V TTL systems without level shifters. Output high-level voltage (VOH) is VCC − 0.2 V minimum at 3 V, and output low-level voltage (VOL) is 0.55 V maximum at 3 V with 64-mA sink current. This mixed-mode capability is intrinsic to the SN74LVTH646PW's design and verified across its full operating temperature range.

Does the SN74LVTH646PW require external pullup or pulldown resistors on its A/B data lines?

No, the SN74LVTH646PW does not require external pullup or pulldown resistors on its A1–A8 or B1–B8 data lines due to integrated bus-hold circuitry. This feature actively maintains valid logic states on unused or floating inputs, with ±500 µA dynamic hold current at VCC = 3.6 V. TI explicitly advises against using external resistors with the bus-hold function, as they may interfere with its operation and degrade noise immunity. The SN74LVTH646PW's bus-hold behavior is fully characterized and guaranteed across temperature and voltage conditions.

How does the SN74LVTH646PW support hot-insertion in backplane systems?

The SN74LVTH646PW supports hot-insertion via two dedicated features: Ioff circuitry and power-up 3-state logic. When VCC = 0 V, Ioff limits leakage current to ±100 µA, preventing damaging backflow from live backplane traces into the unpowered device. During power-up or power-down, the output drivers are forced into high-impedance state regardless of OE or DIR state, eliminating bus contention. These functions are inherent to the SN74LVTH646PW silicon design and require no external components or configuration - confirmed in TI's SCBS705H datasheet under "Hot-Insertion Applications".

What are the timing requirements for reliable register capture on the SN74LVTH646PW?

For reliable register capture, the SN74LVTH646PW requires a minimum CLKAB or CLKBA pulse width (tw) of 3.3 ns and setup/hold times relative to the rising clock edge: tsu = 1.2 ns (min) for A/B data before CLK↑, and th = 0.8 ns (min) after CLK↑ at VCC = 2.7 V. At VCC = 3.3 V, tsu increases to 1.5 ns and th remains 0.8 ns. These values are measured with CL = 50 pF and define the minimum timing window for deterministic data latching into the internal D-type flip-flops - a core function of the SN74LVTH646PW's dual-register architecture.

Can the SN74LVTH646PW operate with a supply voltage below 3.3 V?

Yes, the SN74LVTH646PW is fully specified to operate from 2.7 V to 3.6 V VCC, enabling use with unregulated battery sources down to 2.7 V. At 2.7 V, it maintains 150-MHz clock frequency capability, 64-mA output drive, and full 5-V input tolerance. Electrical characteristics including VOL (0.5 V max), VOH (2.4 V min), and propagation delay (≤5.9 ns) remain guaranteed across this range. This wide VCC window is a defined specification of the SN74LVTH646PW, not a derated condition, and is validated per TI's recommended operating conditions in SCBS705H.