Texas Instruments SN74LVTH646PWR

Overview

SN74LVTH646PWR from Texas Instruments is a 3.3-V octal bus transceiver with registers, supporting mixed-mode 5-V/3.3-V interfacing, hot insertion via Ioff and power-up 3-state, and bus-hold on all data inputs. It provides bidirectional data flow between A and B buses with clocked register storage (CLKAB/CLKBA), direction control (DIR), output enable (OE), and select logic (SAB/SBA) for real-time or stored data routing in high-density memory and address bus applications.

For engineers reviewing the SN74LVTH646PWR datasheet, SN74LVTH646PWR pinout, SN74LVTH646PWR application, or SN74LVTH646PWR equivalent, key selection considerations include its 24-pin TSSOP package, 3.3-V VCC operation with 5-V tolerant inputs, 150-MHz maximum clock frequency, bus-hold functionality eliminating external resistors, and support for hot-plug systems requiring Ioff and controlled power-up sequencing.

Technical Context

The SN74LVTH646PWR integrates eight independent bidirectional channels, each with D-type flip-flop registers clocked on the low-to-high transition of CLKAB (A→B) or CLKBA (B→A). Its dual-register architecture enables simultaneous storage of A- and B-bus data during isolation mode (OE high), while DIR selects active bus direction and SAB/SBA multiplexes between transparent and registered outputs.

It implements true hot-insertion support via Ioff circuitry that disables outputs when VCC = 0 V, preventing backflow current, and power-up 3-state logic that holds outputs high-impedance until VCC stabilizes. Bus-hold inputs maintain valid logic levels on floating A/B pins without external pullups, and VOLP (output ground bounce) remains below 0.8 V at 3.3 V and 25°C.

Key Specifications

Pinout & Package

TSSOP-24 (PW) package: 4.4 mm × 7.8 mm body, 0.65 mm lead 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 SN74LVC646APW, SN74LVTH646PWR adds essential bus-hold and Ioff for rugged industrial use; versus 74ALVCH16646DL, it trades channel count for compact 24-pin TSSOP fit in space-constrained 8-bit control interfaces.

Availability

SN74LVTH646PWR is available at Aetrix Electronics and suitable for memory expansion interfaces, FPGA I/O bridging, hot-swappable backplane modules, and industrial PLC I/O expansion requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SN74LVTH646PWR 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 90 years of innovation in industrial, automotive, and communications markets.

The SN74LVTH646PWR belongs to TI's LVTH logic family, designed specifically for mixed-voltage system interfacing where 3.3-V logic must reliably communicate with 5-V legacy components in high-noise, hot-plug, or battery-powered environments.

FAQ

What is the recommended power-up sequence for SN74LVTH646PWR to ensure reliable hot-insertion behavior?

TI specifies tying OE to VCC through a pullup resistor (minimum value determined by driver sink capability) to guarantee high-impedance state during power ramp. The SN74LVTH646PWR's built-in power-up 3-state circuitry automatically holds all outputs in high-Z until VCC reaches valid operating range (2.7–3.6 V), preventing bus conflicts. No external sequencing logic is needed for the SN74LVTH646PWR itself, though system-level coordination with host controller reset may be required.

Does SN74LVTH646PWR support true 5-V operation on VCC, or is it strictly limited to 3.3-V supply?

The SN74LVTH646PWR is strictly a 3.3-V device: its absolute maximum VCC rating is 4.6 V, and recommended operating range is 2.7 V to 3.6 V. It does not operate at 5 V on VCC. However, its inputs tolerate up to 5.5 V, enabling direct connection to 5-V signal sources while powered from 3.3 V - a key feature of the LVTH family's mixed-mode design.

Can SN74LVTH646PWR be used without external pullup or pulldown resistors on its A and B data lines?

Yes. The SN74LVTH646PWR includes active bus-hold circuitry on all 16 A/B data inputs, which maintains a valid logic state (high or low) on floating pins without external resistors. TI explicitly warns against using pullup/pulldown resistors with bus-hold enabled, as they can cause excessive current draw and logic instability. This feature directly reduces BOM cost and PCB area for the SN74LVTH646PWR.

What is the maximum clock frequency supported by SN74LVTH646PWR for reliable register operation?

The SN74LVTH646PWR supports a maximum clock frequency of 150 MHz across its full operating temperature range (−40°C to 85°C) and VCC range (2.7 V to 3.6 V), as verified in the timing requirements table of the official datasheet SCBS705H. This applies to both CLKAB and CLKBA inputs, enabling high-speed synchronous data capture in memory controllers and FPGA interconnects using the SN74LVTH646PWR.

How does the Ioff specification of SN74LVTH646PWR protect the device during hot insertion?

The Ioff specification (±100 µA maximum at VCC = 0 V) ensures that when the SN74LVTH646PWR is powered down or unpowered during live insertion, its outputs are effectively disabled - blocking damaging current backflow from live 5-V or 3.3-V buses into the device's I/O structures. This protects both the SN74LVTH646PWR and connected components, meeting JESD78 Class II latch-up immunity and enabling safe hot-swap operation in backplane and modular systems.