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Texas Instruments SN74AS646DW
- Part No.:
- SN74AS646DW
- Manufacturer:
- Texas Instruments
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74AS646DW.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 24SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,148
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Product details
Overview
SN74AS646DW 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). It integrates independent D-type flip-flop registers per bus, real-time and stored-data multiplexing via SAB/SBA controls, and supports true (non-inverting) logic path operation. It operates at up to 90 MHz clock frequency with 48 mA low-level output drive, suited for high-speed bus isolation and registered data routing in industrial backplane and legacy computing systems.
For engineers reviewing the SN74AS646DW datasheet, SN74AS646DW pinout, SN74AS646DW application, or SN74AS646DW equivalent, this device is critical for synchronous bus arbitration, dual-mode (transparent/register) data transfer, and noise-immune 3-state bus driving where timing precision, register hold capability, and robust DC drive are required.
Technical Context
The SN74AS646DW implements dual 8-bit bidirectional transceivers with integrated edge-triggered D-flip-flop registers on both A and B buses. Data is latched on the low-to-high transition of CLKAB (A→B) or CLKBA (B→A), enabling synchronized storage independent of direction control.
Its select-control architecture (SAB/SBA) eliminates decoding glitches during transitions between real-time and stored data modes. DIR determines bus direction when OE is active low; OE high places all outputs in high-impedance while preserving input functionality for concurrent register loading.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Function | Octal bus transceiver with independent A/B registers and 3-state outputs - enables simultaneous bus isolation and registered data retention. |
| Max Clock Frequency | 90 MHz - supports high-speed synchronous bus handshaking in legacy microprocessor and memory subsystems. |
| IOL (Low-Level Output) | 48 mA - drives heavy capacitive loads or multiple TTL inputs without external buffers. |
| tPLH / tPHL (CLK→Data) | 2–9 ns - ensures tight setup/hold margins for 90 MHz operation with minimal skew across all eight channels. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded and industrial control applications. |
| VCC Range | 4.5 V to 5.5 V - compatible with standard 5 V logic rails and tolerant of supply ripple. |
| Propagation Delay (A↔B) | 1–11.5 ns - guarantees sub-12 ns bidirectional latency for real-time bus bridging. |
Pinout & Package
SN74AS646DW is housed in a 24-pin SOIC (DW) package with 300-mil width, surface-mount compatible, RoHS-compliant with NiPdAu lead finish and Level-1 moisture sensitivity rating.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 2, 4–11, 13–20 | A1–A8, B1–B8 I/O | Octal bidirectional data terminals - each pair connects to corresponding A/B bus lines; internal 3-state drivers enable bus sharing. |
| 3 | DIR | Direction control - when OE is low, sets data flow direction: DIR = L → B→A; DIR = H → A→B. |
| 21 | OE | Output enable - active-low; disables all outputs to high-impedance while preserving input capture capability. |
| 1, 23 | CLKAB, CLKBA | Edge-triggered clocks - CLKAB↑ latches A-bus data into B-register; CLKBA↑ latches B-bus data into A-register. |
| 2, 22 | SAB, SBA | Select controls - determine whether transceiver outputs reflect real-time (transparent) or stored register data, glitch-free. |
| 12, 24 | GND, VCC | Power supply pins - decoupling required near pin 24 (VCC) and pin 12 (GND) for stable high-speed operation. |
| 14, 15, 16, 17 | NC | No internal connection - must be left unconnected; not tied to ground or voltage. |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B Registers | Enables concurrent storage of data from both buses - supports ping-pong buffering and asynchronous bus synchronization. |
| Glitch-Free Multiplexing | SAB/SBA control logic prevents metastability or transient shorts during mode switching between real-time and stored data paths. |
| True (Non-Inverting) Logic Path | Preserves signal polarity end-to-end - essential for systems requiring deterministic data integrity without inversion compensation. |
| 48 mA IOL Drive Strength | Drives ≥10 standard TTL loads or long PCB traces without fanout buffers - reduces component count in dense backplanes. |
| 90 MHz Max Clock Rate | Meets timing requirements of high-performance 8-bit processors (e.g., Z80, 8085 derivatives) and memory-mapped peripherals. |
Applications
| Industrial Backplane Interfacing | Legacy Microprocessor Bus Expansion |
|---|---|
|
Use Scenario: Isolating and synchronizing data between CPU and peripheral modules across a shared 8-bit backplane with varying propagation delays. IC Role / Device Role / Timing Role: Acts as registered bus transceiver - stores incoming commands/data on CLKAB/CLKBA edges, then forwards them synchronously to reduce timing uncertainty. Use Value: Eliminates race conditions caused by trace-length mismatches; 90 MHz capability supports burst transfers at full system clock rate. |
Use Scenario: Extending address/data bus of an 8085-based controller to support additional RAM, ROM, and I/O devices without degrading timing margins. IC Role / Device Role / Timing Role: Provides direction-controlled, 3-state buffered interface with register hold - allows CPU to read/write peripherals while maintaining bus state during interrupt service. Use Value: 48 mA drive ensures reliable signal integrity across 15+ inch bus runs; NC pins simplify layout by eliminating unused connections. |
| Dual-Mode Data Acquisition Interface | Real-Time + Stored Data Mux System |
|
Use Scenario: Capturing sensor data streams in real time while simultaneously outputting previously acquired calibration values to DACs or displays. IC Role / Device Role / Timing Role: Uses SAB/SBA to switch between live A-bus sensor inputs and pre-loaded B-register calibration constants - no software intervention needed. Use Value: Hardware-selectable data source avoids CPU overhead; glitch-free muxing prevents DAC output spikes during transitions. |
Use Scenario: Implementing a diagnostic bus monitor that captures live bus traffic while replaying known-good test patterns for comparison. IC Role / Device Role / Timing Role: Stores real-time bus activity in A/B registers via CLKAB/CLKBA, then routes stored snapshots to analysis logic using DIR/OE control. Use Value: Independent register control allows capture and playback to occur concurrently - enables real-time fault injection and response validation. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver and register applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS646ADW | ALS family: lower power (ICC ≈ 120 mA vs. 195 mA), slower max clock (40 MHz), 24 mA IOL - uses same DW package and pinout. | Best for low-power, lower-speed systems where 90 MHz is unnecessary and thermal budget is constrained. | Select SN74ALS646ADW when power efficiency > speed; verify timing margins for 40 MHz operation. |
| SN74AS648DW | Inverting logic path (vs. true path of SN74AS646DW); identical speed (90 MHz), drive (48 mA), and package - pin-compatible. | Required where downstream logic expects inverted data or where polarity inversion simplifies board-level signal routing. | Choose SN74AS648DW only if system design explicitly requires inverted data path; otherwise, SN74AS646DW preserves signal polarity. |
Compared with SN74ALS646ADW, SN74AS646DW delivers 2.25× higher clock rate and double the output drive at the cost of ~60% higher ICC; versus SN74AS648DW, it provides true-path operation essential for polarity-critical interfaces without external inverters.
Availability
SN74AS646DW is available at Aetrix Electronics and suitable for industrial backplane interfacing, legacy microprocessor bus expansion, dual-mode data acquisition, and real-time/stored data multiplexing requiring stable component supply and long-term obsolescence management.
Supply support for SN74AS646DW 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 industrial and military-grade components.
The SN74AS646DW belongs to TI's advanced Schottky (AS) logic family, engineered for high-speed, high-drive 5 V digital systems where timing predictability and bus-loading resilience are critical.
FAQ
What is the maximum clock frequency supported by the SN74AS646DW?
The SN74AS646DW supports a maximum clock frequency of 90 MHz under recommended operating conditions (VCC = 4.5 V to 5.5 V, TA = 0°C to 70°C). This specification applies to both CLKAB and CLKBA inputs and is validated per TI's SDAS039F datasheet revision January 1995. The 90 MHz rating enables use in high-speed 8-bit processor bus extensions and real-time data capture systems where minimal propagation delay is essential. SN74AS646DW achieves this performance through advanced Schottky transistor design and optimized internal timing paths.
Does the SN74AS646DW support both real-time and stored data modes?
Yes, the SN74AS646DW supports both real-time (transparent) and stored data modes via its SAB and SBA select-control inputs. When SAB/SBA are asserted, the device routes data directly from the opposing bus (real-time); when deasserted, it outputs data held in the internal A or B registers (stored). The control logic is specifically designed to eliminate decoding glitches during transitions - a key differentiator confirmed in the functional tables and timing diagrams of the SN74AS646DW datasheet. This dual-mode capability is central to its role in diagnostic monitoring and ping-pong buffering applications.
What is the output drive capability of the SN74AS646DW?
The SN74AS646DW provides 48 mA low-level output current (IOL) and –15 mA high-level output current (IOH), measured at VCC = 4.5 V. This drive strength allows the SN74AS646DW to interface directly with up to 10 standard TTL loads or drive long PCB traces without external buffers. The 48 mA rating is particularly valuable in industrial backplane designs where signal integrity over extended distances is critical. Electrical characteristics are specified across the full commercial temperature range (0°C to 70°C) and validated in TI's SDAS039F datasheet.
Is the SN74AS646DW pin-compatible with other devices in the SN74AS64x family?
Yes, the SN74AS646DW is pin-compatible with SN74AS648DW and shares the same 24-pin SOIC (DW) footprint, including identical pin assignments for power (VCC, GND), clocks (CLKAB, CLKBA), controls (OE, DIR, SAB, SBA), and I/O (A1–A8, B1–B8). However, SN74AS646DW implements a true (non-inverting) data path, whereas SN74AS648DW is inverting - this functional difference requires verification in system-level signal polarity analysis. Both devices maintain identical timing, drive, and package specifications, enabling drop-in replacement where logic polarity permits.
What package type and compliance does the SN74AS646DW use?
The SN74AS646DW is supplied in a 24-pin SOIC (DW) package with 300-mil body width, RoHS-compliant with NiPdAu lead finish and Moisture Sensitivity Level 1 (MSL-1, unlimited floor life at ≤30°C/60% RH). It is rated for commercial temperature operation (0°C to 70°C) and features a standard JEDEC MS-013 outline. The DW package supports automated SMT assembly and is documented in TI's packaging addendum (15-Jul-2026). No lead (Pb)-free exemptions apply - SN74AS646DW meets full RoHS Directive 2011/65/EU requirements.
SN74AS646DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AS
- 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, 48mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 24-SOIC
SN74AS646DW FAQ
1.How can I place an order for SN74AS646DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AS646DW 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 SN74AS646DW reliable?
The price and inventory of SN74AS646DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AS646DW is usually 5 days.
3.What payment methods are accepted for SN74AS646DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AS646DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74AS646DW?
SN74AS646DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AS646DW 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 SN74AS646DW?
For technical support, including SN74AS646DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AS646DW requirements.
6.How does Aetrix verify that SN74AS646DW is sourced from the original manufacturer or authorized distributors?
All SN74AS646DW 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 SN74AS646DW meets industry standards.
7.What is the process for return or replacement of SN74AS646DW?
All SN74AS646DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74AS646DW, 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 SN74AS646DW part is unused and in its original packaging.
Return procedure for SN74AS646DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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