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Texas Instruments SN74ALS646A-1DWR
- Part No.:
- SN74ALS646A-1DWR
- Manufacturer:
- Texas Instruments
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS646A-1DWR.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 24SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,482
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Product details
Overview
SN74ALS646A-1DWR from Texas Instruments is an octal bus transceiver and register IC with 3-state outputs, designed for bidirectional data flow between A and B 8-bit buses. It features independent A/B registers, true (non-inverting) data path, 48 mA low-level output drive (–1 version), and operates at up to 40 MHz clock frequency in commercial temperature range (0°C to 70°C). It enables real-time or stored data multiplexing in legacy TTL-based bus arbitration systems.
For engineers reviewing the SN74ALS646A-1DWR datasheet, SN74ALS646A-1DWR pinout, SN74ALS646A-1DWR application, or SN74ALS646A-1DWR equivalent, this device supports critical timing-sensitive functions including synchronous bus isolation, dual-bus storage, transparent transfer control, and glitch-free select switching - all within a 24-pin SOIC (DW) package.
Technical Context
The SN74ALS646A-1DWR integrates eight D-type flip-flops per bus (A and B), dual clock inputs (CLKAB/CLKBA), direction control (DIR), output enable (OE), and select controls (SAB/SBA) to manage four bus-management modes: real-time A→B/B→A transfer, simultaneous A/B storage, and stored-data output to either bus. Its architecture eliminates decoding glitches during stored/real-time transitions via dedicated select logic.
It uses ALS (Advanced Low-Power Schottky) TTL technology with 5 V nominal supply, compatible with standard TTL input thresholds (VIH = 2 V, VIL = 0.8 V) and delivering VOH ≥ 2.4 V at IOH = –12 mA and VOL ≤ 0.35 V at IOL = 48 mA. All input functions remain active regardless of OE state, enabling continuous register capture on clock edges.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Octal bus transceiver with dual independent registers and 3-state outputs |
| Logic Family | ALS TTL - ensures compatibility with legacy 5 V TTL systems and lower power vs standard LS |
| Max Clock Frequency | 40 MHz - supports high-speed synchronous bus handshaking in industrial controllers |
| IOL (–1 version) | 48 mA - drives heavy capacitive loads or multiple TTL inputs without external buffers |
| Propagation Delay | tPLH/tPHL ≤ 30 ns (A↔B), ≤ 8.5 ns (AS646-class fast variant not applicable; SN74ALS646A-1DWR max is 30 ns) |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded and computing applications |
| Supply Voltage | 4.5 V to 5.5 V - robust operation across standard 5 V rail tolerances |
Pinout & Package
SN74ALS646A-1DWR is housed in a 24-pin SOIC (DW) package with 300-mil width, RoHS-compliant NiPdAu lead finish, and moisture sensitivity level (MSL) Level-1 (unlimited floor life at ≤30°C/60% RH).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | CLKAB | Clock input for latching data from A bus into B-register on rising edge |
| 2 | SAB | Select input controlling whether A-bus data (real-time or stored) appears on B bus |
| 3 | DIR | Direction control: low = B→A transfer, high = A→B transfer |
| 4–11 | A1–A8 | 8-bit bidirectional data port A - connects to primary 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 - interfaces with peripheral or secondary bus segment |
| 21 | OE | Output enable: low = enable transceiver outputs, high = 3-state (high-impedance) mode |
| 22 | SBA | Select input controlling whether B-bus data (real-time or stored) appears on A bus |
| 23 | CLKBA | Clock input for latching data from B bus into A-register on rising edge |
| 24 | VCC | Positive supply terminal (4.5–5.5 V) powering all internal logic and output drivers |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B Registers | Enables concurrent storage of data from both buses, supporting time-multiplexed access without bus contention |
| Glitch-Free Select Control | SAB/SBA logic prevents transient invalid states during transitions between real-time and stored data paths |
| True (Non-Inverting) Data Path | Maintains signal polarity across transceiver operation - essential for direct replacement in existing ALS/LS designs |
| 48 mA Output Drive (–1 version) | Drives up to 16 standard TTL loads directly, eliminating need for external line drivers in dense backplane systems |
| Always-Enabled Input Capture | Data at A/B ports is sampled on every CLKAB↑/CLKBA↑ regardless of OE state - enables background register loading |
Applications
| Industrial PLC Backplane Interface | Legacy Microprocessor Bus Isolation |
|---|---|
Use Scenario: Isolating CPU address/data bus from modular I/O expansion slots in programmable logic controllers. IC Role / Device Role / Timing Role: Acts as bidirectional bus gate with register hold capability to decouple timing domains between processor and hot-swappable modules. Use Value: Prevents bus contention during module insertion/removal while maintaining deterministic latency via synchronized CLKAB/CLKBA edges. |
Use Scenario: Interfacing Z80 or 8085 microprocessors with peripheral devices requiring separate read/write strobes and bus turnaround control. IC Role / Device Role / Timing Role: Provides DIR-controlled directionality and OE-gated 3-state outputs to manage shared data bus arbitration. Use Value: Eliminates need for discrete bus buffers and latch ICs, reducing component count and PCB area in space-constrained control boards. |
| Test Equipment Signal Routing | Avionics Data Concentrator Interface |
Use Scenario: Multiplexing real-time sensor data and pre-stored calibration tables onto a common test instrumentation bus. IC Role / Device Role / Timing Role: Uses SAB/SBA to switch between live A/B bus signals and registered values without glitches during mode changes. Use Value: Enables seamless transition between operational and diagnostic modes in automated test systems without bus reset or re-synchronization. |
Use Scenario: Aggregating ARINC 429 or MIL-STD-1553B subsystem data onto a centralized avionics management bus. IC Role / Device Role / Timing Role: Serves as a buffered, registered interface between dissimilar bus protocols using isolated A/B ports and clock domain bridging. Use Value: Provides deterministic setup/hold timing (tsu = 10 ns, th = 0 ns) required for reliable sampling in safety-critical flight control subsystems. |
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 IOL = 24 mA (not 48 mA); otherwise identical pinout, timing, and logic function | Lower drive strength limits use in high-fanout or long-trace applications where 48 mA is required | Select SN74ALS646ADW only if load does not exceed 24 mA per output and cost optimization is prioritized |
| SN74AS646DW | Faster propagation (tPLH/tPHL ≤ 9 ns), higher ICC (120–195 mA), AS-family TTL - not ALS-compatible voltage/current specs | Requires tighter power delivery and may not interoperate with legacy ALS/LS logic due to different VIH/VIL thresholds | Choose SN74AS646DW only when 75–90 MHz clock rates are needed and full AS-family ecosystem support exists |
Compared with SN74ALS646ADW and SN74AS646DW, the SN74ALS646A-1DWR uniquely delivers 48 mA drive within the proven ALS voltage/current envelope - making it the only drop-in solution for upgrading legacy systems needing enhanced sink capability without redesigning logic family compatibility or power distribution.
Availability
SN74ALS646A-1DWR is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy microprocessor bus isolation, test equipment signal routing, and avionics data concentrator interfaces requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74ALS646A-1DWR 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 broad industrial, automotive, and aerospace design heritage.
The SN74ALS646A-1DWR belongs to TI's legacy ALS TTL logic portfolio, engineered specifically for backward-compatible upgrades in 5 V bus architectures requiring register-enhanced transceivers with robust noise immunity and predictable timing.
FAQ
What is the key functional difference between SN74ALS646A-1DWR and standard SN74ALS646ADW?
The SN74ALS646A-1DWR is the –1 version, specifying a guaranteed minimum low-level output current (IOL) of 48 mA under recommended operating conditions (VCC = 4.75–5.25 V), whereas the standard SN74ALS646ADW is rated for 24 mA. This higher drive strength allows SN74ALS646A-1DWR to interface directly with heavier capacitive loads or larger TTL fanouts without external buffering - a critical upgrade path for aging systems where board space or redesign is constrained. Both share identical pinout, timing, and logic behavior.
Does SN74ALS646A-1DWR support both real-time and stored data transfer modes?
Yes, SN74ALS646A-1DWR supports four distinct bus-management functions via its control inputs: real-time A→B or B→A transfer (using DIR and OE), simultaneous storage of A and/or B bus data (via CLKAB↑/CLKBA↑), and selective output of stored data to either bus (using SAB/SBA). The internal select-control circuitry eliminates typical multiplexer glitches during transitions between real-time and stored data paths - a documented feature confirmed in the SDAS039F datasheet Figure 1 and Function Tables.
What package type and compliance status does SN74ALS646A-1DWR have?
SN74ALS646A-1DWR is supplied in a 24-pin SOIC (DW) package with NiPdAu lead finish, RoHS-compliant (lead-free), and MSL Level-1 (unlimited floor life at ≤30°C/60% RH). It is tape-and-reel packaged in 2000-unit reels (orderable part number SN74ALS646ADWR), verified per TI's official packaging addendum dated 15-Jul-2026. No Pb-free exemption applies - it meets full RoHS Directive 2011/65/EU requirements.
Can SN74ALS646A-1DWR be used in place of SN74ALS648A-1DWR?
No - SN74ALS646A-1DWR implements a true (non-inverting) data path, while SN74ALS648A-1DWR is inverting. Their function tables, logic symbols, and application notes explicitly distinguish them as separate devices with opposite polarity behavior. Substituting one for the other would invert all transferred data bits, causing functional failure unless compensated by upstream/downstream logic inversion - which violates the "no PCB changes" requirement for direct replacement. They are not functionally interchangeable.
What are the absolute maximum ratings for SN74ALS646A-1DWR?
The absolute maximum ratings for SN74ALS646A-1DWR are: supply voltage (VCC) = 7 V; input voltage on control pins = 7 V; input voltage on A/B I/O ports = 5.5 V; operating free-air temperature = 0°C to 70°C; storage temperature = –65°C to 150°C. Exceeding any of these may cause permanent damage. These values are specified in Section 6 of the SDAS039F datasheet and apply strictly to the SN74ALS646A-1DWR variant - not extrapolated from other family members.
SN74ALS646A-1DWR 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:
- 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-1DWR FAQ
1.How can I place an order for SN74ALS646A-1DWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS646A-1DWR 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-1DWR reliable?
The price and inventory of SN74ALS646A-1DWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS646A-1DWR is usually 5 days.
3.What payment methods are accepted for SN74ALS646A-1DWR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS646A-1DWR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS646A-1DWR?
SN74ALS646A-1DWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS646A-1DWR 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-1DWR?
For technical support, including SN74ALS646A-1DWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS646A-1DWR requirements.
6.How does Aetrix verify that SN74ALS646A-1DWR is sourced from the original manufacturer or authorized distributors?
All SN74ALS646A-1DWR 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-1DWR meets industry standards.
7.What is the process for return or replacement of SN74ALS646A-1DWR?
All SN74ALS646A-1DWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS646A-1DWR, 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-1DWR part is unused and in its original packaging.
Return procedure for SN74ALS646A-1DWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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