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Texas Instruments SN74ALS646ADWR
- Part No.:
- SN74ALS646ADWR
- Manufacturer:
- Texas Instruments
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS646ADWR.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 24SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,551
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Product details
Overview
SN74ALS646ADWR from Texas Instruments is an octal bus transceiver and register IC with 3-state outputs, designed for bidirectional data flow between two 8-bit buses (A and B). It features independent D-type registers per bus, true (non-inverting) data path, clocked storage on CLKAB/CLKBA rising edges, and real-time or stored data selection via SAB/SBA controls. It operates at up to 40 MHz in commercial temperature range (0°C to 70°C) and is used in legacy industrial control backplanes and buffered address/data bus interfaces.
For engineers reviewing the SN74ALS646ADWR datasheet, SN74ALS646ADWR pinout, SN74ALS646ADWR application, or SN74ALS646ADWR equivalent, key selection criteria include its dual-register architecture, 3-state output drive capability (24 mA sink), DIR/OE-controlled directionality, and compatibility with ALS logic families in space-constrained SOIC-24 layouts.
Technical Context
The SN74ALS646ADWR integrates eight identical channels, each with separate A-side and B-side I/Os, dual D-flip-flop registers (one per bus), and multiplexed output logic enabling simultaneous storage and transparent transfer. Its control architecture uses asynchronous OE for 3-state enable/disable and synchronous DIR to determine data flow direction during active transfer.
Real-time vs. stored data selection is managed by SAB (select A-to-B) and SBA (select B-to-A) inputs, with glitch-free switching achieved via internal priority encoding-eliminating metastability during mode transitions. Clock inputs CLKAB and CLKBA trigger register loading on low-to-high transitions, supporting pipelined bus arbitration in multi-master systems.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | Advanced Low-Power Schottky (ALS), TTL-compatible input thresholds and output drive |
| Bus Width | Octal (8-bit) bidirectional A/B buses with independent register storage |
| Max Clock Frequency | 40 MHz - supports high-speed synchronous bus handshaking in legacy computing systems |
| IOL (Output Sink) | 24 mA - sufficient to drive multiple TTL loads or terminated transmission lines without external buffers |
| Propagation Delay | tPLH/tPHL ≤ 30 ns (A↔B) - ensures timing closure in 25-ns cycle systems with margin |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded and instrumentation applications |
| Supply Voltage | 4.5 V to 5.5 V - robust against rail droop in noisy power environments |
Pinout & Package
SN74ALS646ADWR is housed in a 24-pin SOIC (DW) package, 7.5 mm wide, with standard 0.050″ lead pitch and gull-wing leads. Pin 1 is marked by a beveled corner or notch; pin count follows JEDEC MS-013.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | CLKAB | Clock input for loading data from A bus into A-side register on rising edge |
| 2 | SAB | Select input: enables transfer of stored A data to B bus when DIR=H and OE=L |
| 3 | DIR | Direction control: H = A→B transfer; L = B→A transfer (when OE=L) |
| 4–11 | A1–A8 | 8-bit A-side bidirectional I/O port; inputs when driving B, outputs when driven by B or register |
| 12 | GND | Ground reference for all logic and I/O circuits |
| 13–20 | B1–B8 | 8-bit B-side bidirectional I/O port; symmetric function to A1–A8 |
| 21 | OE | Output enable: L = enable transceiver/register output; H = 3-state isolation |
| 22 | SBA | Select input: enables transfer of stored B data to A bus when DIR=L and OE=L |
| 23 | CLKBA | Clock input for loading data from B bus into B-side register on rising edge |
| 24 | VCC | +5 V supply; decoupling required within 1 cm of pin for noise immunity |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B Registers | Enables concurrent capture of data from both buses, supporting time-multiplexed bus arbitration |
| Glitch-Free Select Logic | SAB/SBA control eliminates decoding glitches during real-time ↔ stored data mode transitions |
| True (Non-Inverting) Data Path | Maintains signal polarity across transceiver operation-critical for address/data integrity in microprocessor buses |
| 3-State Outputs with Asynchronous OE | Allows bus sharing among multiple drivers without contention; OE overrides all other controls |
| SOIC-24 Package | Surface-mount footprint reduces PCB area vs. DIP; compatible with automated assembly and reflow |
Applications
| Industrial Backplane Interface | Legacy Microprocessor Bus Buffer |
|---|---|
Use Scenario: Isolating and synchronizing data between CPU and peripheral modules in modular PLC chassis using shared parallel backplane. IC Role / Device Role / Timing Role: Acts as registered transceiver between CPU address/data bus and slot-specific peripheral bus, providing setup/hold timing margin and drive strength. Use Value: Eliminates need for discrete latches + buffers; supports 40-MHz burst transfers while maintaining signal integrity over 15-cm traces. | Use Scenario: Interfacing Z80 or 8086-based controller to external memory or I/O expansion cards with timing-critical strobes. IC Role / Device Role / Timing Role: Provides direction-controlled, registered data path between processor bus and expansion bus, with OE-gated isolation during DMA cycles. Use Value: Enables clean bus turnaround without external glue logic; 24-mA sink drives 10+ TTL loads directly. |
| Test Equipment Data Acquisition Hub | Avionics Maintenance Interface Adapter |
Use Scenario: Aggregating sensor readings from multiple analog front-ends onto a central diagnostic bus in benchtop test systems. IC Role / Device Role / Timing Role: Captures parallel ADC outputs into local registers, then forwards time-stamped batches to host controller via shared bus. Use Value: Decouples sampling rate from bus transfer rate; prevents data loss during host interrupt latency. | Use Scenario: Adapting legacy ARINC 429 or MIL-STD-1553B subsystem data to ground-support equipment via parallel diagnostics port. IC Role / Device Role / Timing Role: Buffers and registers maintenance data streams before parallel upload, ensuring synchronization with host handshake signals. Use Value: Meets deterministic timing requirements of avionics BIT protocols; SOIC package withstands vibration and thermal cycling. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal registered transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS648ADWR | Inverting data path (A→B and B→A outputs inverted); otherwise identical pinout, timing, and drive specs | Required where bus inversion is part of system-level protocol (e.g., differential pair pre-conditioning or legacy checksum logic) | Select only if system design explicitly requires inverted data; not drop-in replaceable due to functional polarity mismatch |
| SN74AS646DW | Faster propagation (≤9 ns vs. ≤30 ns), higher IOL (48 mA), wider fmax (90 MHz), but higher ICC (120 mA typical) | Suitable for high-speed upgrades where timing budget is tight and power budget allows; not qualified for same thermal envelope | Use when upgrading legacy ALS-based systems to meet tighter setup/hold or higher throughput; verify thermal derating in enclosed enclosures |
Compared with SN74ALS646ADWR, SN74ALS648ADWR provides identical timing and packaging but inverts data-requiring logic inversion elsewhere in the system-while SN74AS646DW delivers significantly faster performance at the cost of higher power and reduced noise margin, making it suitable only for speed-critical redesigns.
Availability
SN74ALS646ADWR is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy microprocessor bus buffering, and test equipment data acquisition requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS646ADWR 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 SN74ALS646A series belongs to TI's legacy bipolar logic portfolio, engineered for robustness and compatibility in mission-critical industrial control and military-grade systems where reliability and long-term support are essential.
FAQ
What is the maximum clock frequency supported by the SN74ALS646ADWR?
The SN74ALS646ADWR supports a maximum clock frequency of 40 MHz under recommended operating conditions (VCC = 4.5 V to 5.5 V, TA = 0°C to 70°C). This rating applies to both CLKAB and CLKBA inputs and is validated across process, voltage, and temperature corners. Exceeding 40 MHz may result in register setup/hold violations or metastability in the storage path. The SN74ALS646ADWR datasheet specifies minimum pulse widths (12.5 ns high/low) to ensure reliable edge detection.
Does the SN74ALS646ADWR support hot-swap or live-insertion?
No, the SN74ALS646ADWR does not support hot-swap or live-insertion. Its absolute maximum ratings specify that VCC must be applied before any input or I/O signal, and removal of VCC while signals are present may cause latch-up or damage. The device lacks bus-hold, power-on reset, or Ioff protection circuitry. For hot-swap applications, external current-limiting resistors and sequencing controllers are required-TI recommends evaluating newer alternatives like the SN74AVC series if live insertion is mandatory.
How does the SN74ALS646ADWR handle simultaneous access to both A and B buses?
When OE is low, the SN74ALS646ADWR permits only one-directional data flow at a time-controlled strictly by the DIR input. If DIR = H, A bus data drives B bus (real-time or stored); if DIR = L, B bus data drives A bus. Simultaneous bidirectional driving is electrically prohibited by design. However, both A and B registers can be loaded concurrently (via CLKAB↑ and CLKBA↑), and their contents retained during OE = H isolation-enabling coordinated, non-conflicting data staging.
Can the SN74ALS646ADWR be used with 3.3-V logic systems?
The SN74ALS646ADWR is not designed for direct 3.3-V operation. Its recommended VCC range is 4.5 V to 5.5 V, and its input thresholds (VIH = 2.0 V min, VIL = 0.8 V max) are TTL-compatible-not LVCMOS. Driving its inputs from 3.3-V logic may result in marginal noise margins or undefined states. Level-shifting (e.g., TI SN74AVC4T245) or supply translation is required. The SN74ALS646ADWR output VOH/VOL specs assume 5-V rails; connecting to 3.3-V inputs without clamping risks overvoltage damage.
What is the purpose of the NC pins on the SN74ALS646ADWR?
The SN74ALS646ADWR has no NC (No Connect) pins in its SOIC-24 (DW) package. All 24 pins are assigned functions as defined in the official TI datasheet SDAS039F. Any reference to "NC" in schematic symbols or layout notes pertains to legacy ceramic DIP (JT) variants where certain pins were unused-but the DW package fully utilizes all positions. Always refer to the DW-specific pinout diagram (page 1 of SDAS039F) to confirm connectivity; misinterpreting pin 12 (GND) or pin 24 (VCC) as NC would cause catastrophic failure.
SN74ALS646ADWR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 24-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tape & Reel (TR)
- 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
SN74ALS646ADWR FAQ
1.How can I place an order for SN74ALS646ADWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS646ADWR 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 SN74ALS646ADWR reliable?
The price and inventory of SN74ALS646ADWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS646ADWR is usually 5 days.
3.What payment methods are accepted for SN74ALS646ADWR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS646ADWR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS646ADWR?
SN74ALS646ADWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS646ADWR 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 SN74ALS646ADWR?
For technical support, including SN74ALS646ADWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS646ADWR requirements.
6.How does Aetrix verify that SN74ALS646ADWR is sourced from the original manufacturer or authorized distributors?
All SN74ALS646ADWR 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 SN74ALS646ADWR meets industry standards.
7.What is the process for return or replacement of SN74ALS646ADWR?
All SN74ALS646ADWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS646ADWR, 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 SN74ALS646ADWR part is unused and in its original packaging.
Return procedure for SN74ALS646ADWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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