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Texas Instruments SN74ALS646A-1DW
- Part No.:
- SN74ALS646A-1DW
- Manufacturer:
- Texas Instruments
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS646A-1DW.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 24SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,268
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Product details
Overview
SN74ALS646A-1DW 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, real-time or stored data multiplexing via SAB/SBA controls, true (non-inverting) logic path, and a -1 version rated for 48 mA low-level output current at 5 V. It is used in legacy industrial control backplanes requiring synchronized bus isolation and register hold.
For engineers reviewing the SN74ALS646A-1DW datasheet, SN74ALS646A-1DW pinout, SN74ALS646A-1DW application, or SN74ALS646A-1DW equivalent, key selection criteria include its 24-pin SOIC (DW) package, dual-clock (CLKAB/CLKBA) edge-triggered storage, DIR/OE-controlled transceiver mode, and guaranteed 40 MHz max clock frequency under commercial temperature range (0°C to 70°C).
Technical Context
This device integrates eight parallel D-type flip-flops per bus (A and B), enabling simultaneous latching of 8-bit data on rising edges of CLKAB or CLKBA. Its select-control circuitry (SAB/SBA) eliminates decoding glitches during transitions between real-time and stored data paths.
Direction (DIR) and output-enable (OE) inputs jointly govern bus directionality and 3-state output drive capability. In isolation mode (OE high), A and B data may be independently stored without bus contention; only one bus (A or B) may be actively driven at any time.
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. |
| Max Clock Frequency | 40 MHz - supports high-speed synchronous bus transfers in real-time or registered modes. |
| IOL (–1 version) | 48 mA - enables direct driving of multiple TTL loads or termination-resistor networks without external buffers. |
| Propagation Delay (tPLH/tPHL) | 7–30 ns - guarantees timing margins for 25 ns clock cycles in register-to-bus or bus-to-bus transfer paths. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded systems, not extended/military temperature operation. |
| Supply Voltage Range | 4.5 V to 5.5 V - tight regulation required; operation outside this range risks latch-up or parameter violation. |
| Package Type | 24-pin SOIC (DW) - surface-mount, 300-mil width, RoHS-compliant NiPdAu lead finish, MSL Level-1. |
Pinout & Package
SN74ALS646A-1DW uses a 24-pin SOIC (DW) package with 300-mil body width, gull-wing leads, and standard pin 1 marking notch. Pinout follows TI's DW package layout for octal transceivers.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | CLKAB | Rising-edge clock for latching data from A bus into B-side register. |
| 2 | SAB | Select input controlling whether real-time or stored B data appears on A bus. |
| 3 | DIR | Direction control: low = B→A transfer; high = A→B transfer (when OE active). |
| 4–11 | A1–A8 | 8-bit bidirectional data port A - connects to source system bus or microprocessor data lines. |
| 12 | GND | Ground reference for all internal logic and I/O circuits. |
| 13–20 | B1–B8 | 8-bit bidirectional data port B - connects to destination bus, peripheral interface, or memory subsystem. |
| 21 | OE | Output enable: low = transceiver active; high = all outputs in high-impedance state. |
| 22 | SBA | Select input controlling whether real-time or stored A data appears on B bus. |
| 23 | CLKBA | Rising-edge clock for latching data from B bus into A-side register. |
| 24 | VCC | +5 V supply - must be decoupled locally; tolerance ±5% per recommended operating conditions. |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B registers | Enables concurrent capture and retention of data from both buses - critical for handshake-free dual-bus arbitration. |
| Glitch-free select control (SAB/SBA) | Eliminates metastability during real-time ↔ stored data switching - avoids spurious bus transients in synchronous designs. |
| True (non-inverting) data path | Maintains signal polarity across transceiver mode - simplifies timing analysis and avoids inversion logic in PCB routing. |
| 48 mA IOL (–1 version) | Drives up to 12 standard TTL loads directly - reduces need for external line drivers in dense backplane applications. |
| Isolation mode with OE high | Allows A and/or B data to be held in registers while both buses float - essential for safe hot-swap or diagnostic states. |
Applications
| Industrial Backplane Interface | Legacy Microprocessor Bus Extension |
|---|---|
|
Use Scenario: Interfacing a 16-bit CPU bus to an 8-bit peripheral expansion slot with synchronized handshaking. IC Role / Device Role / Timing Role: Acts as a registered bus transceiver that isolates CPU address/data from peripheral timing domains while preserving data integrity across clock domain boundaries. Use Value: Enables deterministic read/write cycles using stored data mode during wait-state insertion, eliminating bus contention during peripheral latency. |
Use Scenario: Extending a Z80 or 8085-based control system with additional I/O modules via shared data bus. IC Role / Device Role / Timing Role: Provides bidirectional, direction-controlled data transfer between CPU and peripheral cards, with register hold for multi-cycle instruction execution. Use Value: Allows CPU to pre-load command data into B-side register while executing other instructions, then burst-transfer to peripheral on next CLKBA edge. |
| Programmable Logic Controller (PLC) I/O Module | Test Equipment Data Capture Buffer |
|
Use Scenario: Isolating field I/O signals from controller logic in modular PLC racks with hot-swap capability. IC Role / Device Role / Timing Role: Functions as a buffered, register-hold interface between isolated I/O backplane and main controller bus. Use Value: Maintains last valid I/O state in registers during module insertion/removal, preventing transient glitches on controller bus. |
Use Scenario: Capturing parallel digital waveform data from DUTs in automated test equipment before serial upload. IC Role / Device Role / Timing Role: Latches 8-bit parallel samples on CLKAB/CLKBA edges and holds them for controlled readout via DIR/OE sequencing. Use Value: Supports real-time sampling at up to 40 MHz while decoupling acquisition timing from slower host processor read cycles. |
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 | No -1 suffix: rated for 24 mA IOL (not 48 mA); otherwise identical pinout, timing, and logic function. | Lower drive strength limits use in high-fanout or unterminated transmission line scenarios. | Select when load count ≤ 6 TTL units or when lower power consumption is prioritized over drive margin. |
| SN74AS646DW | Faster propagation (2–9 ns vs 7–30 ns), higher ICC (120–211 mA), 90 MHz fmax, but same 24-pin DW package and pin compatibility. | Supports higher-speed systems but requires tighter power delivery and thermal management. | Choose for new designs targeting >40 MHz operation where ALS speed/power trade-off is insufficient. |
Compared with SN74ALS646A-1DW, SN74ALS646ADW offers lower drive and power, while SN74AS646DW delivers significantly faster timing at higher supply current - both retain full pin and functional compatibility for drop-in replacement where electrical margins permit.
Availability
SN74ALS646A-1DW is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy microprocessor bus extensions, and programmable logic controller (PLC) I/O modules requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74ALS646A-1DW 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 product line delivers robust octal bus transceivers with integrated registers for legacy TTL system upgrades and industrial control infrastructure - emphasizing reliability, timing precision, and backward compatibility.
FAQ
What is the primary function of the SN74ALS646A-1DW in a digital system?
The SN74ALS646A-1DW functions as an octal bidirectional bus transceiver with dual independent registers, enabling synchronized, glitch-free data transfer between two 8-bit buses (A and B). It supports real-time pass-through or stored-data output via SAB/SBA controls, and its -1 version provides 48 mA low-level output drive for demanding TTL fanout requirements. This makes SN74ALS646A-1DW ideal for industrial backplane and legacy microprocessor interfacing where register hold and bus isolation are critical.
How does the SN74ALS646A-1DW differ from the standard SN74ALS646ADW?
The SN74ALS646A-1DW differs from SN74ALS646ADW solely in its guaranteed low-level output current rating: 48 mA versus 24 mA. All other parameters - pinout, timing, logic function, package, and temperature range - are identical. The -1 suffix indicates enhanced drive capability for applications requiring higher sink current, such as driving unterminated stubs or multiple TTL inputs. SN74ALS646A-1DW remains fully pin- and function-compatible with SN74ALS646ADW.
Can the SN74ALS646A-1DW operate with a 3.3 V supply?
No, the SN74ALS646A-1DW is an ALS TTL device specified only for 4.5 V to 5.5 V operation. It is not 3.3 V compatible: VIH minimum is 2.0 V, but VCC must be ≥4.5 V for correct internal biasing and output voltage levels (VOH ≥2.4 V, VOL ≤0.4 V). Using 3.3 V will result in undefined logic states, excessive ICC, and potential damage due to improper transistor biasing. Always power SN74ALS646A-1DW from a regulated 5 V rail.
What is the role of the DIR and OE pins on the SN74ALS646A-1DW?
On the SN74ALS646A-1DW, OE (output enable) controls 3-state output drivers: when high, all A and B port outputs enter high-impedance mode regardless of DIR state. DIR (direction) determines bus flow direction only when OE is low: DIR = low enables B→A transfer; DIR = high enables A→B transfer. Critically, input receivers remain active even when OE is high - allowing continued data capture into registers while outputs are disabled. This dual-control architecture enables flexible bus arbitration in SN74ALS646A-1DW designs.
Is the SN74ALS646A-1DW pin-compatible with the SN74AS646DW?
Yes, the SN74ALS646A-1DW is pin-compatible with SN74AS646DW: both use the 24-pin SOIC (DW) package with identical pin assignments for CLKAB, CLKBA, DIR, OE, SAB, SBA, A1–A8, B1–B8, VCC, and GND. However, they differ electrically: SN74AS646DW operates at higher speed (90 MHz fmax, 2–9 ns delays) and draws more supply current (up to 211 mA), while SN74ALS646A-1DW offers lower power and 48 mA IOL. System-level validation of timing and power is required before substitution.
SN74ALS646A-1DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 24-SOIC (0.295", 7.50mm Width)
- 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:
- 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
SN74ALS646A-1DW FAQ
1.How can I place an order for SN74ALS646A-1DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS646A-1DW 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 SN74ALS646A-1DW reliable?
The price and inventory of SN74ALS646A-1DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS646A-1DW is usually 5 days.
3.What payment methods are accepted for SN74ALS646A-1DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS646A-1DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS646A-1DW?
SN74ALS646A-1DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS646A-1DW 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 SN74ALS646A-1DW?
For technical support, including SN74ALS646A-1DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS646A-1DW requirements.
6.How does Aetrix verify that SN74ALS646A-1DW is sourced from the original manufacturer or authorized distributors?
All SN74ALS646A-1DW 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 SN74ALS646A-1DW meets industry standards.
7.What is the process for return or replacement of SN74ALS646A-1DW?
All SN74ALS646A-1DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS646A-1DW, 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 SN74ALS646A-1DW part is unused and in its original packaging.
Return procedure for SN74ALS646A-1DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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