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Texas Instruments SN74ALS646ADW
- Part No.:
- SN74ALS646ADW
- Manufacturer:
- Texas Instruments
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS646ADW.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 24SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:140
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Product details
Overview
SN74ALS646ADW from Texas Instruments is an octal bus transceiver and register IC with 3-state outputs, designed for bidirectional data flow between A and B buses in TTL-compatible systems. It features independent A/B registers, true (non-inverting) data path, real-time or stored data multiplexing via SAB/SBA controls, and operates at up to 40 MHz clock frequency over 0°C to 70°C. It is used in legacy industrial control backplanes requiring registered bus isolation and glitch-free data switching.
For engineers reviewing the SN74ALS646ADW datasheet, SN74ALS646ADW pinout, SN74ALS646ADW application, or SN74ALS646ADW equivalent, this device supports critical timing-critical bus management functions including simultaneous storage and transparent transfer, direction-controlled transceivers, and isolated register hold - all within a 24-pin SOIC (DW) package compliant with JEDEC MS-013.
Technical Context
The SN74ALS646ADW integrates eight D-type flip-flops per bus (A and B), dual clock inputs (CLKAB, CLKBA), and select-control logic (SAB, SBA) that eliminates decoding glitches during transitions between real-time and stored data modes. Its DIR input determines data direction during transceiver operation, while OE enables/disables 3-state outputs without disabling input functionality.
It implements independent register storage for both buses, allowing asynchronous capture of A or B bus data on low-to-high clock edges, and supports four fundamental bus-management functions: real-time A→B or B→A transfer, storage from either bus, and output of stored data to either or both buses - all configurable via OE, DIR, SAB, and SBA.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | Advanced Low-Power Schottky (ALS) TTL - ensures compatibility with legacy 5 V TTL systems and reduced power vs standard LS. |
| Bus Width | Octal (8-bit) bidirectional - supports full parallel data paths for A and B buses without external multiplexing. |
| Max Clock Frequency | 40 MHz - enables high-speed synchronous register loading in real-time bus arbitration applications. |
| Output Type | 3-state non-inverting - allows wired-OR bus sharing and clean signal isolation when disabled. |
| Supply Voltage Range | 4.5 V to 5.5 V - tight regulation tolerance supports stable operation across industrial 5 V rails. |
| Operating Temperature | 0°C to 70°C - commercial-grade rating suitable for embedded controllers and instrumentation. |
| IOL (Low-Level Output) | 24 mA (standard version) - sufficient drive strength for TTL fanout of 20+ loads without buffering. |
Pinout & Package
SN74ALS646ADW uses a 24-pin SOIC (DW) package per JEDEC MS-013, 300-mil body width, with gull-wing leads and RoHS-compliant NiPdAu plating. Pin 1 is marked by a beveled corner or notch orientation.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | CLKAB | Clock input for latching data from A bus into B-register - rising edge triggers storage. |
| 2 | SAB | Select A→B: L = real-time A→B transfer; H = stored A→B transfer - glitch-free transition logic. |
| 3 | DIR | Direction control: L = B→A; H = A→B - active during OE = L, defines transceiver data flow path. |
| 4–11 | A1–A8 | Bus A I/O terminals - bidirectional ports supporting both input capture and output driving. |
| 12 | GND | Ground reference - single ground pin shared across logic and I/O sections. |
| 13–20 | B1–B8 | Bus B I/O terminals - functionally symmetric to A-bus with independent register storage. |
| 21 | OE | Output enable: H = 3-state (high-Z); L = active output - does not disable input capture capability. |
| 22 | SBA | Select B→A: L = real-time B→A; H = stored B→A - paired with SAB for full multiplex control. |
| 23 | CLKBA | Clock input for latching data from B bus into A-register - rising edge triggers storage. |
| 24 | VCC | Positive supply - must be decoupled locally; supports 4.5–5.5 V operation with 5 V nominal. |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B Registers | Enables concurrent capture and retention of data from both buses - critical for handshake-free bus arbitration. |
| Glitch-Free Multiplexing | SAB/SBA control logic prevents metastability or transient shorts during stored↔real-time mode switching. |
| Input-Enabled During Output Disable | Data capture continues on CLKAB/CLKBA edges even when OE = H - supports background monitoring. |
| True (Non-Inverting) Data Path | Preserves signal polarity end-to-end - required for direct replacement in legacy ALS/LS designs. |
| SOIC (DW) Package | 24-pin surface-mount footprint with 1.27 mm pitch - compatible with automated assembly and space-constrained PCBs. |
Applications
| Industrial Backplane Interface | Legacy System Bus Isolation |
|---|---|
Use Scenario: Interfacing microprocessor local bus to modular I/O chassis via passive backplane. IC Role / Device Role / Timing Role: Bidirectional registered transceiver managing address/data strobes between CPU and peripheral slots. Use Value: Eliminates timing skew between slots using synchronized register hold, enabling deterministic multi-drop communication. |
Use Scenario: Replacing obsolete 74LS646 in repair of 1980s-era CNC controller mainboards. IC Role / Device Role / Timing Role: Drop-in functional replacement with identical pinout, voltage thresholds, and propagation delays. Use Value: Maintains original system timing margins while improving reliability and availability over discontinued parts. |
| Programmable Logic Glue Logic | Dual-Bus Data Arbitration |
Use Scenario: Connecting FPGA configuration bus to external PROM and diagnostic port simultaneously. IC Role / Device Role / Timing Role: Registered bus switch enabling time-multiplexed access to shared memory resources. Use Value: Allows FPGA to read PROM during boot and later route debug data through same pins without contention. |
Use Scenario: Arbitrating between two independent 8-bit microcontrollers sharing a common display driver bus. IC Role / Device Role / Timing Role: Direction-controlled transceiver with storage registers preventing bus collisions during handshaking. Use Value: Enables one MCU to pre-load display data into registers while the other drives the bus - zero-cycle conflict resolution. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal registered transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS648ADW | Inverting data path (A→B and B→A outputs inverted); otherwise identical pinout, timing, and register architecture. | Required where system-level logic polarity mandates inversion (e.g., complemented control bus signaling). | Select only if inverting behavior matches downstream interface requirements - not a drop-in replacement for true-path designs. |
| SN74AS646DW | Faster propagation (≤9 ns vs ≤30 ns), higher drive (48 mA IOL), but wider supply range (4.5–5.5 V) and same 0°C–70°C temp grade. | Suitable for new designs needing higher speed or drive strength; requires validation of timing closure due to faster edges. | Prefer for performance-critical upgrades; verify layout integrity for AS-family edge rates and ensure adequate decoupling. |
Compared with SN74ALS646ADW, SN74ALS648ADW provides identical functionality with inverted outputs - useful for polarity-matched interfaces - while SN74AS646DW delivers significantly improved speed and drive at the cost of stricter layout and noise control requirements.
Availability
SN74ALS646ADW is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system repairs, programmable logic glue logic, and dual-bus arbitration applications requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74ALS646ADW 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 with deep heritage in TTL and advanced logic families.
The SN74ALS646ADW belongs to TI's legacy Advanced LS (ALS) logic product line, engineered specifically for high-reliability, pin-compatible replacements in industrial and military-grade systems requiring robust 5 V TTL interoperability.
FAQ
What is the maximum clock frequency supported by the SN74ALS646ADW?
The SN74ALS646ADW supports a maximum clock frequency of 40 MHz under recommended operating conditions (VCC = 4.5 V to 5.5 V, CL = 50 pF). This rating applies to both CLKAB and CLKBA inputs and is validated across the full 0°C to 70°C operating temperature range. The device achieves this speed while maintaining guaranteed setup/hold times and propagation delays consistent with ALS family specifications.
Does the SN74ALS646ADW support true or inverting data paths?
The SN74ALS646ADW implements a true (non-inverting) data path - data appearing on A1–A8 appears unmodified on B1–B8 during real-time transfer, and vice versa. This distinguishes it from the SN74ALS648ADW, which provides an inverting path. The truth table and logic diagrams in the official datasheet SDAS039F confirm non-inverting behavior for SN74ALS646ADW across all operational modes.
Can the SN74ALS646ADW retain stored data while outputs are disabled?
Yes. When OE is high (3-state mode), the SN74ALS646ADW disables its A and B bus outputs but maintains full register functionality: CLKAB and CLKBA continue to capture data from their respective buses into internal storage registers, and SAB/SBA controls remain active for selecting stored vs. real-time data. Input capture is always enabled regardless of OE state.
What package type is used for the SN74ALS646ADW?
The SN74ALS646ADW uses a 24-pin SOIC (DW) package per JEDEC MS-013, with 300-mil body width, gull-wing leads, and RoHS-compliant NiPdAu terminal finish. It is rated for moisture sensitivity level (MSL) 1 at 260°C peak reflow, and carries the top-marking "ALS646A". This package is distinct from the ceramic DIP (JT) and plastic DIP (NT) variants used in military-grade versions.
How does the SN74ALS646ADW handle bus contention during direction switching?
The SN74ALS646ADW prevents bus contention through strict directional control: only one bus (A or B) may drive the other at any time, enforced by the DIR input in conjunction with OE. When DIR = L and OE = L, only B→A transfer is enabled; when DIR = H and OE = L, only A→B is enabled. Simultaneous drive is physically impossible due to internal gating - no external bus-keeper resistors are required.
SN74ALS646ADW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- 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:
- 15mA, 24mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 24-SOIC
SN74ALS646ADW FAQ
1.How can I place an order for SN74ALS646ADW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS646ADW 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 SN74ALS646ADW reliable?
The price and inventory of SN74ALS646ADW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS646ADW is usually 5 days.
3.What payment methods are accepted for SN74ALS646ADW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS646ADW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS646ADW?
SN74ALS646ADW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS646ADW 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 SN74ALS646ADW?
For technical support, including SN74ALS646ADW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS646ADW requirements.
6.How does Aetrix verify that SN74ALS646ADW is sourced from the original manufacturer or authorized distributors?
All SN74ALS646ADW 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 SN74ALS646ADW meets industry standards.
7.What is the process for return or replacement of SN74ALS646ADW?
All SN74ALS646ADW units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS646ADW, 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 SN74ALS646ADW part is unused and in its original packaging.
Return procedure for SN74ALS646ADW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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