Texas Instruments SN74LVC646APWT

Overview

SN74LVC646APWT from Texas Instruments is an octal bus transceiver and register with 3-state outputs, designed for 1.65-V to 3.6-V VCC operation. It features dual-clock control (CLKAB/CLKBA), direction (DIR) and select (SAB/SBA) inputs, 8-bit A/B bidirectional data paths, and Ioff partial-power-down support. It enables real-time or registered data transfer between buses in mixed-voltage systems (3.3-V/5-V).

For engineers reviewing the SN74LVC646APWT datasheet, SN74LVC646APWT pinout, SN74LVC646APWT application, or SN74LVC646APWT equivalent, key selection criteria include its 24-pin TSSOP package, 7.4 ns max propagation delay at 3.3 V, 150 MHz clock frequency capability, and support for isolated storage of A- and B-bus data during OE high.

Technical Context

The SN74LVC646APWT integrates eight D-type flip-flops with dual-clock edge-triggered capture (CLKAB for A→register, CLKBA for B→register), enabling synchronized latching from either bus. Its transceiver mode supports real-time bidirectional flow controlled by DIR and OE, while SAB/SBA allow multiplexing between transparent and registered data paths.

It implements Ioff circuitry to disable outputs and prevent backflow current during partial power-down, and accepts 5.5-V-tolerant inputs across all ports - a critical feature for voltage translation between 3.3-V logic and legacy 5-V subsystems without external level shifters.

Key Specifications

Pinout & Package

TSSOP-24 package (PW), 7.8 mm × 4.4 mm body, 0.65 mm lead pitch, 1.2 mm max height, exposed pad not present.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVC646APWR and SN74LVC646ADBR, the SN74LVC646APWT provides identical logic behavior and timing in a tube-packaged TSSOP variant ideal for engineering evaluation and low-volume integration - avoiding reel-handling overhead while retaining full electrical equivalence.

Availability

SN74LVC646APWT is available at Aetrix Electronics and suitable for industrial PLC backplane interfaces, FPGA-to-MCU bridges, automotive BCM subsystems, test equipment pattern generators, and mixed-voltage embedded control applications requiring stable component supply and long-term sourcing continuity.

Supply support for SN74LVC646APWT 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 company headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, personal electronics, and communications markets.

The SN74LVC646A product line delivers advanced bus management ICs with integrated registers and 3-state outputs, engineered specifically for voltage translation, synchronous data routing, and isolation in resource-constrained embedded systems.

FAQ

What is the maximum clock frequency supported by SN74LVC646APWT?

The SN74LVC646APWT supports a maximum clock frequency of 150 MHz across its recommended operating range (1.65 V to 3.6 V). This value is specified under load conditions with CL = 50 pF and applies to both CLKAB and CLKBA inputs, enabling high-speed synchronous data capture in demanding digital interfaces such as memory-mapped peripherals or FPGA interconnects. The SN74LVC646APWT achieves this while maintaining guaranteed setup and hold times of 1.6 ns and 1.7 ns respectively at 3.3 V.

Does SN74LVC646APWT support partial power-down operation?

Yes, the SN74LVC646APWT includes Ioff circuitry that actively disables outputs when VCC is near 0 V, preventing damaging current backflow from live I/O lines into the unpowered device. This feature is fully characterized per JESD 78 and allows safe integration into systems with staggered power sequencing - for example, when the SN74LVC646APWT's VCC is off but connected to a 5-V bus. The Ioff leakage is limited to ±10 µA at 5.5 V, ensuring minimal impact on upstream drivers.

Can SN74LVC646APWT translate between 5-V and 3.3-V logic levels?

Yes, the SN74LVC646APWT accepts input voltages up to 5.5 V regardless of VCC level (1.65–3.6 V), making it suitable for translating 5-V signals to 3.3-V domains. Its outputs swing rail-to-rail (VOL ≈ 0.4 V, VOH ≈ VCC – 0.2 V at 3.3 V), so downstream 3.3-V receivers see valid logic levels. However, it does not translate 3.3-V outputs to 5-V - for bidirectional translation, two SN74LVC646APWT devices or a dedicated level shifter is required.

What is the purpose of the SAB and SBA pins on SN74LVC646APWT?

The SAB and SBA pins on the SN74LVC646APWT control multiplexing between real-time (transparent) and registered (latched) data paths. When SAB is low, stored A-bus data is routed to the B-bus; when high, real-time A-bus data passes through. Similarly, SBA low selects stored B-bus data for A-bus output. These pins enable flexible bus arbitration - for instance, holding diagnostic data in register while continuing real-time sensor reads - without requiring external logic or additional clock cycles.

How does the DIR pin affect data flow direction in SN74LVC646APWT?

The DIR pin on the SN74LVC646APWT determines the primary direction of active transceiver flow when OE is low: DIR = low enables B→A transfer (B-bus data appears on A-bus), and DIR = high enables A→B transfer (A-bus data appears on B-bus). DIR has no effect when OE is high (isolation mode) or during register capture (CLKAB/CLKBA edges). Its logic level is sampled synchronously with OE, ensuring glitch-free direction switching aligned to bus enable timing.