Texas Instruments SN74LVTH646NSR

Overview

SN74LVTH646NSR 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 features dual-clock (CLKAB/CLKBA), direction control (DIR), output enable (OE), and select controls (SAB/SBA) for multiplexed A↔B data routing in industrial backplanes and legacy system upgrades.

For engineers reviewing the SN74LVTH646NSR datasheet, SN74LVTH646NSR pinout, SN74LVTH646NSR application, or SN74LVTH646NSR equivalent, key selection considerations include 3.3-V VCC operation with 5-V tolerant I/O, 150-MHz clock frequency support, bus-hold elimination of external resistors, and NS package thermal performance (θJA = 65°C/W).

Technical Context

The SN74LVTH646NSR integrates eight bidirectional data channels with independent D-type flip-flop registers per bus (A and B), enabling simultaneous storage and real-time transfer. Its dual-clock architecture allows asynchronous latching: CLKAB captures A-bus data to internal register, CLKBA captures B-bus data - both triggered on low-to-high transitions.

Control logic implements four distinct operational modes: real-time transceiver (OE low + DIR set), stored-data transceiver (OE low + SAB/SBA asserted), isolation (OE high), and register-only storage (CLKAB/CLKBA active, OE high). Bus-hold circuitry maintains valid logic levels on floating A/B inputs without external pull resistors.

Key Specifications

Pinout & Package

SN74LVTH646NSR uses a 24-pin SOP (Small Outline Package) with 0.65-mm lead pitch, body dimensions 7.9 mm × 4.5 mm × 1.75 mm max height, and JEDEC MO-153 compliant footprint. Thermal resistance θJA = 65°C/W enables reliable operation in compact industrial PCB layouts without forced airflow.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVC646PWR, SN74LVTH646NSR delivers stronger drive, integrated bus-hold, and superior 5-V tolerance - critical for mixed-voltage reliability. Versus SN74LVCH16646DLR, it offers pin-compatible 8-bit functionality in smaller NS package, simplifying layout in space-constrained modules.

Availability

SN74LVTH646NSR is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system upgrade bridges, and hot-swappable module carriers requiring stable component supply across extended temperature ranges (−40°C to 85°C).

Supply support for SN74LVTH646NSR 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 decades of experience in industrial-grade logic and interface solutions.

The SN74LVTH646NSR belongs to TI's LVTH (Low-Voltage BiCMOS Transistor-Transistor Logic) family, engineered for robust mixed-signal interfacing in harsh environments where voltage translation, hot insertion, and latch-up immunity are mission-critical.

FAQ

What is the maximum clock frequency supported by the SN74LVTH646NSR?

The SN74LVTH646NSR supports a maximum clock frequency of 150 MHz under recommended operating conditions (VCC = 3.3 V ± 0.3 V, TA = −40°C to 85°C). This rating applies to both CLKAB and CLKBA inputs and is verified with CL = 50 pF load. At lower VCC (2.7 V), the device still achieves 150 MHz, ensuring timing margin in battery-powered or brownout scenarios. The SN74LVTH646NSR datasheet specifies this in the "Timing Requirements" table on page 7.

Does the SN74LVTH646NSR require external pullup or pulldown resistors on its A/B data lines?

No, the SN74LVTH646NSR does not require external pullup or pulldown resistors on its A1–A8 or B1–B8 data inputs because it integrates active bus-hold circuitry. This feature maintains unused or floating inputs at a valid logic level using ±500 µA dynamic hold current (at VCC = 3.6 V). Using external resistors with the SN74LVTH646NSR bus-hold is explicitly discouraged in the datasheet (page 2) as it may interfere with proper operation.

Can the SN74LVTH646NSR be used in hot-swap applications?

Yes, the SN74LVTH646NSR is specifically designed for hot-insertion applications. It incorporates two key protections: Ioff circuitry that disables outputs and limits current to ±100 µA when VCC = 0 V, preventing damaging backflow; and power-up 3-state logic that forces outputs into high-impedance during power ramp-up/down. These features are validated per JESD 78 and documented in the "Features" section (page 1) and "Electrical Characteristics" table (page 6) of the SN74LVTH646NSR datasheet.

What is the thermal resistance (θJA) of the SN74LVTH646NSR in its NS package?

The SN74LVTH646NSR in the SOP (NS) package has a junction-to-ambient thermal resistance (θJA) of 65°C/W, as specified in the "Absolute Maximum Ratings" table (page 5) of the datasheet. This value assumes standard JEDEC 2-layer board conditions and enables reliable operation up to 85°C ambient when dissipating ≤150 mW. For higher-power use cases, thermal vias under the exposed pad (if present) or copper pour should be added per TI's PCB guidelines.

How does the SN74LVTH646NSR handle 5-V input signals while operating from a 3.3-V supply?

The SN74LVTH646NSR accepts input voltages up to 5.5 V on all A/B data, control, and clock pins while powered from a 2.7–3.6-V VCC rail. Its input structure includes clamping diodes and robust oxide design, allowing safe interfacing with 5-V TTL systems without external level shifters. This mixed-mode capability is confirmed in the "Recommended Operating Conditions" table (page 5) and "Absolute Maximum Ratings" (VI = −0.5 V to 7 V), making the SN74LVTH646NSR ideal for upgrading legacy 5-V infrastructure.