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Texas Instruments SN74HCT646NT
- Part No.:
- SN74HCT646NT
- Manufacturer:
- Texas Instruments
- Package:
- 24-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74HCT646NT.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 24DIP
- Quantity:
- Payment:
- Shipping:
Inventory:2,477
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Product details
Overview
SN74HCT646NT from Texas Instruments is an octal bus transceiver and register IC with 3-state outputs, designed for bidirectional data flow control between two 8-bit buses (A and B) in TTL-compatible systems. It features independent clocked D-type registers per bus, real-time or stored data multiplexing via SAB/SBA controls, ±6-mA output drive at 5 V, 12 ns typical propagation delay, and operates within 4.5 V to 5.5 V supply range.
For engineers reviewing the SN74HCT646NT datasheet, SN74HCT646NT pinout, SN74HCT646NT application, or SN74HCT646NT equivalent, key selection criteria include its dual-register storage capability, DIR/OE-controlled transceiver mode, TTL-input compatibility, 24-pin PDIP (NT) package thermal profile (θJA = 67°C/W), and support for isolated bus hold during OE high.
Technical Context
The SN74HCT646NT implements synchronous bus management using two independent edge-triggered clocks (CLKAB and CLKBA) to latch data into separate A- and B-bus registers on low-to-high transitions. Its logic combines transparent transceiver paths with registered storage, enabling four distinct functions: real-time A→B/B→A transfer, stored-data A↔B transfer, simultaneous A/B storage, and isolation mode with retained register contents.
Control is managed through DIR (data direction), OE (output enable), and select inputs SAB/SBA that determine whether real-time or registered data appears at outputs. All control inputs are TTL-voltage compatible (VIL ≤ 0.8 V, VIH ≥ 2 V), and the device maintains input functionality even when outputs are disabled - allowing register updates during 3-state operation.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage | 4.5 V to 5.5 V - ensures stable operation across standard 5-V TTL/CMOS mixed-signal systems. |
| Propagation Delay | 12 ns typical at 5.5 V - enables reliable timing in high-speed 8-bit bus interfaces up to 29 MHz clock rate. |
| Output Drive | ±6 mA at 5 V - directly drives up to 15 LSTTL loads without external buffers. |
| Input Current | 1 µA max - minimizes loading on upstream TTL or CMOS drivers. |
| Quiescent ICC | 80 µA max - supports low-power system standby modes while retaining register state. |
| Logic Family | HCT - provides TTL-input compatibility with CMOS power efficiency and noise immunity. |
| Operating Temp | –40°C to +85°C - qualified for industrial-grade embedded and control applications. |
Pinout & Package
SN74HCT646NT is housed in a 24-pin plastic dual in-line package (PDIP-NT), with 67°C/W junction-to-ambient thermal resistance. Pin numbering follows standard JEDEC outline for NT packages, with GND at pin 11 and VCC at pin 24.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 2, 4–10, 12–13, 15–20 | A1–A8, B1–B8 I/O | Octal bidirectional data terminals; function as inputs or 3-state outputs depending on DIR/OE state. |
| 3, 21–23 | DIR, OE, SAB, SBA | Direction, output enable, and select controls - determine data path (real-time vs. stored) and bus directionality. |
| 1, 23 | CLKAB, CLKBA | Edge-triggered clocks - latch A-bus data on CLKAB↑, B-bus data on CLKBA↑; asynchronous to each other. |
| 11 | GND | Ground reference for all internal logic and I/O structures. |
| 24 | VCC | Positive supply rail - must be decoupled locally due to switching current transients. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent registers | Enables concurrent storage of A- and B-bus data - critical for handshake protocols and pipeline buffering. |
| Multiplexed real-time/stored data | SAB/SBA inputs allow dynamic selection between live bus signals and latched register contents without re-clocking. |
| TTL-compatible inputs | Accepts standard TTL logic thresholds (VIH ≥ 2 V, VIL ≤ 0.8 V) - eliminates level-shifting in mixed-logic systems. |
| High-current 3-state outputs | ±6-mA drive strength supports direct interfacing to legacy LSTTL loads and reduces need for external drivers. |
| Isolation mode with retention | When OE = high, both buses float but register contents remain intact - preserves state during bus arbitration or power sequencing. |
Applications
| Industrial PLC Backplane | Legacy Microprocessor Bus Interface |
|---|---|
Use Scenario: Interfacing multiple I/O modules to a central controller over a shared 8-bit data bus with deterministic timing and fault isolation. IC Role / Device Role / Timing Role: Bidirectional bus transceiver and register buffer - manages data flow between CPU and peripheral cards while holding status registers during bus contention. Use Value: Eliminates need for discrete latches and direction-control logic; enables synchronized read-modify-write cycles via registered storage. | Use Scenario: Connecting Z80 or 8085-based systems to memory-mapped peripherals requiring address/data separation and bus turnaround control. IC Role / Device Role / Timing Role: Octal transceiver with clocked registers - provides controlled data handoff between CPU AD bus and peripheral data lines with precise setup/hold timing. Use Value: Meets strict tsu/th requirements (20 ns/5 ns at 4.5 V); supports both burst and single-cycle transfers via DIR/OE sequencing. |
| Test Equipment Data Acquisition | Automated Test Fixture Control |
Use Scenario: Capturing parallel sensor outputs and routing them to a digitizer or FPGA under programmable timing control. IC Role / Device Role / Timing Role: Registered bus interface - samples analog-to-digital converter outputs synchronously and holds values until host processor initiates readback. Use Value: Reduces sampling jitter by eliminating combinatorial path delays; allows CPU to service other tasks while data remains stable in registers. | Use Scenario: Controlling relay banks, LED arrays, or solenoid drivers from a microcontroller with limited GPIO, requiring buffered and latched outputs. IC Role / Device Role / Timing Role: Output register and driver - stores command words from MCU and presents them simultaneously to high-current loads via 3-state outputs. Use Value: Prevents spurious actuation during partial writes; enables glitch-free updates using CLKAB-triggered strobing. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal transceiver-and-register applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74HCT245N | No internal registers; only transceiver function with DIR/OE control - lacks clocked storage capability. | Suitable for simple bidirectional data transfer without intermediate latching or multiplexed real-time/stored operation. | Select when bus isolation and direction control suffice, and register retention is unnecessary. |
| SN74ACT646N | ACT family - higher speed (tpd ≈ 8 ns), wider VCC range (4.5–5.5 V), but higher ICC (100 µA typ) and no TTL-input compatibility. | Better suited for high-frequency digital systems where speed outweighs power or legacy interface requirements. | Choose when operating above 30 MHz or when driving ACT loads; avoid if interfacing with TTL sources. |
Compared with SN74HCT646NT, SN74HCT245N omits register functionality entirely - simplifying design but removing storage and multiplexing capabilities - while SN74ACT646N trades TTL compatibility and lower quiescent current for faster propagation and higher drive, making it appropriate only in fully ACT-optimized environments.
Availability
SN74HCT646NT is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy microprocessor bus interfaces, and automated test fixture control requiring stable component supply, long-term lifecycle support, and verified PDIP packaging for through-hole manufacturing.
Supply support for SN74HCT646NT 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 founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.
The SN74HCT646NT belongs to TI's 74HCT logic family - engineered to deliver TTL-compatible input thresholds with CMOS power efficiency, targeting robust interoperability in mixed-technology digital systems.
FAQ
What is the primary function of the SN74HCT646NT in a digital system?
The SN74HCT646NT serves as an octal bidirectional bus transceiver with integrated D-type registers, enabling controlled data movement between two 8-bit buses (A and B) while supporting both real-time and stored-data transfer modes. Its core function is to manage bus arbitration, isolate subsystems, and retain data state - all within a single 24-pin PDIP package. The SN74HCT646NT achieves this through dedicated clock inputs (CLKAB/CLKBA), direction control (DIR), output enable (OE), and select lines (SAB/SBA), making it ideal for systems requiring deterministic timing and register-backed buffering.
How does the SN74HCT646NT handle power-up and power-down sequencing?
To ensure high-impedance outputs during power transitions, the OE pin of the SN74HCT646NT must be tied to VCC through a pullup resistor - minimum value determined by the driver's current-sinking capability. This prevents bus contention or unintended signal injection when VCC is ramping. The SN74HCT646NT itself draws only 80 µA max quiescent current and tolerates supply voltages from 4.5 V to 5.5 V, supporting graceful entry into and exit from operational states without latch-up or undefined behavior.
Can the SN74HCT646NT operate with mixed-voltage logic families?
The SN74HCT646NT accepts TTL-level inputs (VIL ≤ 0.8 V, VIH ≥ 2 V) while operating from a 5-V supply, making it compatible with standard TTL, LS-TTL, and 74HCT-series outputs. However, it is not designed for direct interfacing with 3.3-V or lower logic families without level translation - its inputs do not tolerate voltages exceeding VCC, and its outputs swing rail-to-rail (0 V to 5 V). For mixed-voltage systems, the SN74HCT646NT should be used exclusively in 5-V domains or paired with dedicated translators.
What is the significance of the "NT" suffix in SN74HCT646NT?
"NT" denotes the plastic dual in-line package (PDIP) variant of the SN74HCT646NT, manufactured by Texas Instruments. This package has 24 leads, through-hole mounting, and a thermal resistance of θJA = 67°C/W - higher than the SOIC-DW version (46°C/W) due to less efficient heat dissipation. The NT suffix distinguishes it from other variants like SN74HCT646DW (SOIC) and ensures mechanical and thermal compatibility with legacy PCB layouts requiring DIP footprints.
Does the SN74HCT646NT support hot insertion or live bus swapping?
The SN74HCT646NT does not include built-in hot-swap protection features such as power-on reset, slew-rate limiting, or bus-fault tolerance. While its 3-state outputs can be controlled via OE to isolate the device from the bus, safe hot insertion requires external circuitry - including current-limiting resistors, TVS diodes, and controlled power ramping - to prevent damage from voltage overshoot or ground bounce. System-level validation is required before deploying the SN74HCT646NT in live-swappable modules.
SN74HCT646NT Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74HCT
- Package/Case:
- 24-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Obsolete
- 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:
- Through Hole
- Supplier Device Package:
- 24-PDIP
SN74HCT646NT FAQ
1.How can I place an order for SN74HCT646NT through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74HCT646NT 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 SN74HCT646NT reliable?
The price and inventory of SN74HCT646NT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74HCT646NT is usually 5 days.
3.What payment methods are accepted for SN74HCT646NT?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74HCT646NT transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74HCT646NT?
SN74HCT646NT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74HCT646NT 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 SN74HCT646NT?
For technical support, including SN74HCT646NT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74HCT646NT requirements.
6.How does Aetrix verify that SN74HCT646NT is sourced from the original manufacturer or authorized distributors?
All SN74HCT646NT 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 SN74HCT646NT meets industry standards.
7.What is the process for return or replacement of SN74HCT646NT?
All SN74HCT646NT units undergo pre-shipment inspection (PSI). If there is an issue with SN74HCT646NT, 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 SN74HCT646NT part is unused and in its original packaging.
Return procedure for SN74HCT646NT:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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