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Home > Products > Integrated Circuits (ICs) > Logic > Buffers, Drivers, Receivers, Transceivers

Texas Instruments SN74HCT646DW

Name: SN74HCT646DW
Brand: Texas Instruments
SKU: SN74HCT646DW
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: SN74HCT646DW

Manufacturer:: Texas Instruments

Category:: Buffers, Drivers, Receivers, Transceivers

Package:: 24-SOIC (0.295", 7.50mm Width)

Datasheet:: SN74HCT646DW.pdf

Description:: IC TXRX NON-INVERT 5.5V 24SOIC

Quantity:: RFQ Add To RFQ list

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Product details

Overview

SN74HCT646DW from Texas Instruments is an octal bus transceiver and register IC with 3-state outputs, operating at 4.5 V to 5.5 V, delivering 12 ns typical propagation delay, ±6-mA output drive at 5 V, and low 80-µA max ICC. It supports bidirectional real-time or registered data transfer between A and B 8-bit buses in industrial control backplanes and legacy system upgrades.

For engineers reviewing the SN74HCT646DW datasheet, SN74HCT646DW pinout, SN74HCT646DW application, or SN74HCT646DW equivalent, key selection criteria include clock-controlled register storage (CLKAB/CLKBA), independent SAB/SBA multiplexing of live/stored data, DIR/OE-controlled direction and 3-state enable, and TTL-compatible inputs for mixed-logic interfacing.

Technical Context

The SN74HCT646DW integrates eight identical bidirectional channels, each with D-type flip-flops clocked on low-to-high transitions of CLKAB (A→B) or CLKBA (B→A), enabling synchronized capture of data from either bus. Its dual-register architecture allows concurrent storage of A-bus and B-bus data under isolation mode (OE high).

Transceiver operation is governed by DIR (data flow direction) and OE (output enable), while SAB and SBA select between real-time (transparent) or stored data paths per bus. All control inputs-DIR, OE, SAB, SBA, CLKAB, CLKBA-are TTL-voltage compatible and support full 5-V CMOS logic levels.

Key Specifications

Parameter	Value and Actual Design Meaning
Supply Voltage	4.5 V to 5.5 V - Ensures compatibility with standard 5-V TTL and CMOS systems without level-shifting.
Propagation Delay (tpd)	12 ns typical at 5.5 V - Enables reliable operation in high-speed 24–29 MHz clock domains with CL = 50 pF.
Output Drive	±6 mA at 5 V - Directly drives up to 15 LSTTL loads, eliminating need for external buffers in legacy bus interfaces.
Input Current (II)	1 µA max - Minimizes loading on upstream drivers and supports high-fanout bus topologies.
3-State Leakage (IOZ)	±5 µA max - Guarantees robust high-impedance isolation during bus contention or power sequencing.
Power Consumption (ICC)	80 µA max - Supports low-static-power designs in always-on industrial control modules.
Operating Temperature	–40°C to +85°C - Qualified for extended industrial environments including factory automation and test equipment.

Pinout & Package

SN74HCT646DW is housed in a 24-pin SOIC (DW) package with 300-mil body width, JEDEC MS-013 compliant, RoHS-compliant NiPdAu lead finish, and MSL Level-1 rating for unlimited reflow.

Pin/Terminal	Circuit Role	Design Meaning
1, 2, 3, 4, 5, 6, 7, 8 A1–A8	A-bus data I/O	8-bit bidirectional port connected to local subsystem; latched on CLKAB↑ when DIR = H or CLKBA↑ when DIR = L.
13, 14, 15, 16, 17, 18, 19, 20 B1–B8	B-bus data I/O	8-bit bidirectional port linked to main system bus; functions as source or sink depending on DIR and OE state.
2, 22 SAB, SBA	Data path select	SAB controls A→B path (L = real-time, H = stored); SBA controls B→A path (L = real-time, H = stored).
1, 23 CLKAB, CLKBA	Register clock inputs	CLKAB↑ captures A-bus data into B-register; CLKBA↑ captures B-bus data into A-register - edge-triggered, asynchronous enable.
3 DIR	Direction control	H enables A→B transfer; L enables B→A transfer - active regardless of OE state, but output only enabled when OE = L.
21 OE	Output enable	Active-low; disables all 3-state outputs (A/B ports) while preserving input functionality for register capture during isolation.
12 GND	Ground reference	Primary signal return; must be low-impedance connection to minimize noise coupling in shared-bus applications.
24 VCC	Power supply	+5 V supply rail; requires local 0.1-µF ceramic decoupling adjacent to pin to suppress switching noise.

Key Features

Feature	Design Value
Dual independent registers	Enables simultaneous storage of A-bus and B-bus data, supporting time-critical arbitration and glitch-free bus handoff.
Multiplexed real-time/stored data paths	SAB/SBA inputs allow dynamic selection between live bus signals and previously latched values without clock intervention.
TTL-compatible inputs	Accepts standard 0.8 V / 2.0 V logic thresholds - eliminates external level shifters when interfacing with legacy 74LS or 74ALS devices.
High-current 3-state outputs	±6 mA drive strength ensures clean signal integrity across long PCB traces or multi-drop bus stubs up to 15 LSTTL loads.
Isolation-mode register retention	When OE = H, A/B data remain latched and stable - critical for safe hot-swap or partial-system reset scenarios.

Applications

Industrial Backplane Interface	Legacy System Bus Extension
Use Scenario: Interfacing a modern microcontroller module to a legacy 8-bit ISA-style backplane carrying address/data/control lines. IC Role / Device Role / Timing Role: Bidirectional bus transceiver with register hold capability, synchronizing burst transfers between mismatched clock domains using CLKAB/CLKBA edges. Use Value: Eliminates timing skew between CPU and peripheral cards by latching A-bus addresses before asserting B-bus strobes, ensuring setup/hold compliance across variable propagation delays.	Use Scenario: Adding isolated diagnostic access to a running embedded controller's internal data bus without disrupting real-time operation. IC Role / Device Role / Timing Role: Registered bus buffer configured in isolation mode (OE = H) to capture and hold snapshot of A-bus activity while B-bus remains active. Use Value: Enables non-intrusive debug probing via B-bus readout of stored A-bus values - no bus contention or cycle stealing required.
Programmable Logic Controller (PLC) I/O Expansion	Test Equipment Data Capture Module
Use Scenario: Expanding digital I/O capacity in a modular PLC rack where field-side signals must be synchronized with master scan cycles. IC Role / Device Role / Timing Role: Octal register-transceiver acting as interface between slow-scanning CPU bus and fast-response field I/O modules. Use Value: Captures field input states on CLKBA↑, holds them until next scan cycle, then forwards via DIR/OE-controlled transfer - prevents metastability in deterministic scan loops.	Use Scenario: Capturing parallel data streams from DUTs (device under test) in automated test fixtures with precise timestamp alignment. IC Role / Device Role / Timing Role: Synchronized data latch and bus driver, triggered by test sequencer clocks (CLKAB/CLKBA) to sample DUT outputs on defined edges. Use Value: Provides deterministic, jitter-free sampling window (tsu = 23 ns min, th = 5 ns min) and clean 3-state isolation during result readout phases.

Industrial Backplane Interface

Legacy System Bus Extension

Use Scenario: Interfacing a modern microcontroller module to a legacy 8-bit ISA-style backplane carrying address/data/control lines.

IC Role / Device Role / Timing Role: Bidirectional bus transceiver with register hold capability, synchronizing burst transfers between mismatched clock domains using CLKAB/CLKBA edges.

Use Value: Eliminates timing skew between CPU and peripheral cards by latching A-bus addresses before asserting B-bus strobes, ensuring setup/hold compliance across variable propagation delays.

Use Scenario: Adding isolated diagnostic access to a running embedded controller's internal data bus without disrupting real-time operation.

IC Role / Device Role / Timing Role: Registered bus buffer configured in isolation mode (OE = H) to capture and hold snapshot of A-bus activity while B-bus remains active.

Use Value: Enables non-intrusive debug probing via B-bus readout of stored A-bus values - no bus contention or cycle stealing required.

Programmable Logic Controller (PLC) I/O Expansion

Test Equipment Data Capture Module

Use Scenario: Expanding digital I/O capacity in a modular PLC rack where field-side signals must be synchronized with master scan cycles.

IC Role / Device Role / Timing Role: Octal register-transceiver acting as interface between slow-scanning CPU bus and fast-response field I/O modules.

Use Value: Captures field input states on CLKBA↑, holds them until next scan cycle, then forwards via DIR/OE-controlled transfer - prevents metastability in deterministic scan loops.

Use Scenario: Capturing parallel data streams from DUTs (device under test) in automated test fixtures with precise timestamp alignment.

IC Role / Device Role / Timing Role: Synchronized data latch and bus driver, triggered by test sequencer clocks (CLKAB/CLKBA) to sample DUT outputs on defined edges.

Use Value: Provides deterministic, jitter-free sampling window (tsu = 23 ns min, th = 5 ns min) and clean 3-state isolation during result readout phases.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
SN74HCT245DW	No internal registers; purely transparent 3-state transceiver with DIR/OE only - lacks CLKAB/CLKBA, SAB/SBA, and storage capability.	Suitable only for real-time bus buffering without synchronization or data hold requirements.	Select SN74HCT245DW when clocked registration and multiplexed stored/real-time paths are unnecessary and lower gate count is prioritized.
SN74ACT646DW	ACT family: higher speed (fmax = 64 MHz vs 29 MHz), lower noise margin (VIH = 2.0 V min), and higher ICC (100 µA typ vs 80 µA max).	Better suited for high-frequency test equipment but less tolerant of marginal TTL input noise or voltage droop.	Choose SN74ACT646DW only if system clock exceeds 27 MHz and supply stability is guaranteed; otherwise SN74HCT646DW offers superior noise immunity and lower static power.

Compared with SN74HCT245DW, SN74HCT646DW adds essential register synchronization and multiplexed data path control - critical for deterministic timing in industrial controllers. Against SN74ACT646DW, it trades peak speed for wider noise margins and lower quiescent current, making it more robust in electrically noisy factory-floor environments.

Availability

SN74HCT646DW is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus extensions, programmable logic controller (PLC) I/O expansion, and automated test equipment requiring stable component supply across long production lifecycles.

Supply support for SN74HCT646DW 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 founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74HCT646DW belongs to TI's 74HCT logic family - designed specifically for TTL-compatible 5-V systems requiring low power, high noise immunity, and seamless integration with legacy bipolar logic without level translation.

FAQ

What is the primary function of the SN74HCT646DW in a bus interface design?

The SN74HCT646DW serves as an octal registered transceiver that enables bidirectional, clock-synchronized data transfer between two 8-bit buses (A and B). Unlike basic transceivers, it incorporates dual D-type registers and multiplexed data-path control (via SAB/SBA), allowing designers to route either real-time or previously latched data - making SN74HCT646DW ideal for deterministic timing in industrial backplanes and legacy system upgrades where bus arbitration and glitch-free handoff are critical.

Can the SN74HCT646DW operate reliably with 3.3-V logic inputs?

No - the SN74HCT646DW is specified for 4.5 V to 5.5 V operation and features TTL-compatible input thresholds (VIH = 2.0 V min, VIL = 0.8 V max), not 3.3-V CMOS levels. Applying 3.3-V signals risks marginal or non-functional behavior due to insufficient noise margin. For mixed-voltage systems, use a dedicated level shifter or select a 3.3-V–tolerant logic family; SN74HCT646DW requires strict 5-V supply and interface voltages to meet its published timing and drive specifications.

How does the SN74HCT646DW handle power-up sequencing to avoid bus contention?

To ensure high-impedance outputs during power-up or power-down, the OE pin of the SN74HCT646DW must be tied to VCC through a pull-up resistor - TI specifies minimum resistance based on driver sink capability. This forces OE = high at power-on, placing all A/B outputs in 3-state mode before logic stabilization. The SN74HCT646DW's internal registers retain last-stored data during this period, but no bus driving occurs until OE is actively driven low - preventing contention on shared data lines during system initialization.

What is the significance of the SAB and SBA pins on the SN74HCT646DW?

SAB and SBA are independent select-control inputs that determine whether real-time (transparent) or stored data appears on the respective A→B or B→A data paths. When SAB = L, A-bus data passes directly to B-bus outputs; when SAB = H, the previously latched value from the A-register is forwarded instead. Similarly, SBA selects between live B-bus input or stored B-register content for A-bus output. This dual-mux capability makes SN74HCT646DW uniquely suited for applications requiring dynamic switching between live monitoring and captured snapshots - such as diagnostic modes in PLCs or test equipment.

Does the SN74HCT646DW support hot-swap or live insertion into an active bus?

The SN74HCT646DW supports controlled hot-swap operation when OE is held high (via pull-up) during insertion, ensuring all outputs remain in high-impedance state until fully powered and initialized. Its inputs remain functional even with OE high, allowing immediate capture of bus data upon power stabilization. However, mechanical insertion must avoid shorting pins, and VCC ramp rate should comply with TI's recommended 100 ms max rise time. Full hot-swap robustness also depends on system-level protection (e.g., series resistors, bus terminators); SN74HCT646DW itself provides no built-in ESD or overvoltage hardening beyond standard HCT ratings.

SN74HCT646DW Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: 74HCT

Package/Case:: 24-SOIC (0.295", 7.50mm Width)

Packaging:: Bulk

Product Status:: Active

Logic Type:: Transceiver, Non-Inverting

Number of Elements:: 1

Number of Bits per Element:: 8

Input Type:: -

Output Type:: 3-State

Current - Output High, Low:: 6mA, 6mA

Voltage - Supply:: 4.5V ~ 5.5V

Operating Temperature:: -40°C ~ 85°C (TA)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 24-SOIC

SN74HCT646DW FAQ

1.How can I place an order for SN74HCT646DW through Aetrix?

Please submit a Request for Quotation (RFQ) for SN74HCT646DW on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for SN74HCT646DW reliable?

The price and inventory of SN74HCT646DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74HCT646DW is usually 5 days.

3.What payment methods are accepted for SN74HCT646DW?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74HCT646DW transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for SN74HCT646DW?

SN74HCT646DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your SN74HCT646DW order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for SN74HCT646DW?

For technical support, including SN74HCT646DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74HCT646DW requirements.

6.How does Aetrix verify that SN74HCT646DW is sourced from the original manufacturer or authorized distributors?

All SN74HCT646DW products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SN74HCT646DW meets industry standards.

7.What is the process for return or replacement of SN74HCT646DW?

All SN74HCT646DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74HCT646DW, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The SN74HCT646DW part is unused and in its original packaging.

Return procedure for SN74HCT646DW:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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