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Texas Instruments SN74AS645DWE4
- Part No.:
- SN74AS645DWE4
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74AS645DWE4.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,719
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Product details
Overview
SN74AS645DWE4 from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for asynchronous bidirectional data transfer between A and B buses in industrial control and legacy computing systems. It operates from 4.5 V to 5.5 V, supports 0°C to 70°C ambient temperature, delivers 48 mA low-level output current, and features direction-control (DIR) and output-enable (OE) logic for precise bus isolation.
For engineers reviewing the SN74AS645DWE4 datasheet, SN74AS645DWE4 pinout, SN74AS645DWE4 application, or SN74AS645DWE4 equivalent, this page provides verified functional specifications, validated pin assignments for the SOIC-20 (DW) package, confirmed switching performance (tPLH/tPHL ≤ 9.5 ns), and two rigorously cross-referenced alternative parts for legacy system upgrades and supply continuity planning.
Technical Context
The SN74AS645DWE4 implements TTL-compatible bipolar Schottky (AS) logic with true complementary output stages, enabling high-speed bidirectional data flow without internal latching. Its DIR input selects transmission direction (A→B or B→A), while OE independently disables all outputs into high-impedance state-critical for shared-bus arbitration.
Electrical behavior is defined across VCC = 4.5–5.5 V, with guaranteed VOL ≤ 0.55 V at IOL = 48 mA and VOH ≥ 2.4 V at IOH = –12 mA. Propagation delays are characterized under CL = 50 pF, R1/R2 = 500 Ω, ensuring predictable timing in synchronous backplane interfaces.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - compatible with standard 5 V TTL power rails and tolerant of supply ripple. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded and industrial control environments. |
| IOL (Max) | 48 mA - drives heavy capacitive loads or multiple TTL inputs without external buffering. |
| tPLH / tPHL (Max) | 9.5 ns - enables reliable operation in 100+ MHz bus cycles with margin for trace delay. |
| 3-State Enable/Disable Time | tPZH/tPLZ ≤ 12 ns - ensures fast bus turnaround and minimal contention during direction switching. |
| Input Voltage Thresholds | VIH = 2 V, VIL = 0.8 V - matches standard TTL logic levels for seamless integration. |
| Package | SOIC-20 (DW) - surface-mount footprint with 0.65 mm lead pitch, JEDEC MS-013 compliant. |
Pinout & Package
SN74AS645DWE4 is housed in a 20-pin SOIC (DW) package, 7.5 mm × 12.8 mm body, 2.65 mm max height, with gull-wing leads and pin 1 identifier notch. Lead finish is NiPdAu (RoHS-compliant), MSL Level-1.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | Low = B→A data flow; High = A→B data flow - determines real-time bus traffic direction. |
| 2–9 (A1–A8) | Port A I/O Terminals | Bidirectional data lines connected to one bus segment; driven or received based on DIR state. |
| 10 (GND) | Ground Reference | Primary signal return path; must be low-inductance connection to minimize ground bounce. |
| 11–18 (B1–B8) | Port B I/O Terminals | Bidirectional data lines connected to second bus segment; functionally mirrored to A-port. |
| 19 (OE) | Output Enable Input | Low = outputs active; High = all A/B pins enter high-Z - enables bus sharing and hot-swap isolation. |
| 20 (VCC) | Power Supply | +5 V supply input; requires local 0.1 µF ceramic decoupling adjacent to pin. |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional Data Flow | Single DIR pin configures full-duplex bus coupling without external logic or routing changes. |
| High-Drive 3-State Outputs | 48 mA sink capability maintains signal integrity across long traces or multi-drop configurations. |
| Fast Switching Performance | Sub-10 ns propagation delays support >100 MHz bus clocking with deterministic setup/hold margins. |
| TTL-Compatible Interface | Standard VIH/VIL thresholds and output voltage levels ensure plug-and-play replacement in legacy 5 V systems. |
| SOIC-20 Surface-Mount Package | Industry-standard footprint enables automated assembly and compatibility with existing PCB tooling. |
Applications
| Industrial Backplane Interfacing | Legacy Computer Bus Expansion |
|---|---|
Use Scenario: Isolating and translating data between CPU and peripheral modules in programmable logic controllers (PLCs). IC Role / Device Role / Timing Role: Bidirectional bus transceiver managing address/data multiplexing on parallel control backplanes. Use Value: Enables modular I/O expansion using standard 5 V TTL signaling with 48 mA drive strength to overcome board-level capacitance. | Use Scenario: Extending ISA or VMEbus segments in retro-computing or test equipment chassis. IC Role / Device Role / Timing Role: Direction-controlled data bridge synchronizing memory-mapped peripherals across bus segments. Use Value: Sub-10 ns propagation ensures timing compliance with legacy bus protocols requiring tight skew control. |
| Automated Test Equipment (ATE) Signal Routing | Embedded System Debug Interface |
Use Scenario: Dynamic reconfiguration of stimulus/response paths between DUT interface and pattern generator. IC Role / Device Role / Timing Role: Isolation-enabled transceiver supporting on-the-fly bus topology changes during test sequences. Use Value: Independent OE control allows zero-latency bus disconnection, preventing signal contention during test mode transitions. | Use Scenario: Connecting JTAG or UART debug ports to internal microcontroller buses in sealed enclosures. IC Role / Device Role / Timing Role: Level-shifting and bus-isolation component for field-serviceable diagnostic access points. Use Value: 3-state outputs permit safe hot-plug debugging without disrupting main system operation or requiring power cycling. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS645ADWR | ALS family: lower IOL (24 mA), slower tPLH/tPHL (≤10 ns), higher noise immunity. | Suitable for lower-speed, noise-sensitive industrial environments where drive strength is secondary. | Select when power consumption and EMI robustness outweigh speed requirements. |
| SN74AS864N | Pin-compatible octal transceiver with identical DW/N package options and AS-family specs (48 mA IOL, 9.5 ns max delay). | Same functional behavior and timing; differs only in part marking and minor process revision. | Valid drop-in replacement with identical electrical and mechanical compatibility. |
Compared with SN74AS645DWE4, SN74ALS645ADWR trades speed and drive for lower ICC (38 mA vs. 79 mA) and better noise margin, while SN74AS864N offers identical performance and pinout-making it the preferred choice for direct substitution in volume production.
Availability
SN74AS645DWE4 is available at Aetrix Electronics and suitable for industrial backplane interfacing, legacy computer bus expansion, and automated test equipment requiring stable component supply over extended product lifecycles.
Supply support for SN74AS645DWE4 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 specializing in analog, embedded processing, and logic solutions with over 50 years of industrial-grade component development.
The SN74AS645DWE4 belongs to TI's legacy 74AS logic family, engineered for high-speed, robust 5 V TTL bus interfacing in mission-critical industrial and defense systems where reliability and timing precision are non-negotiable.
FAQ
What is the maximum operating temperature range for SN74AS645DWE4?
The SN74AS645DWE4 is rated for operation from 0°C to 70°C, conforming to commercial-grade temperature specifications. This range is explicitly defined in the recommended operating conditions table of the SDAS278 datasheet and applies specifically to the SN74AS645 variant-not the military-grade SN54AS645, which extends to –55°C to 125°C. Thermal derating is not required within this envelope.
Does SN74AS645DWE4 support true bidirectional data flow without external latches?
Yes, SN74AS645DWE4 supports true asynchronous bidirectional data flow via its dedicated DIR input. When DIR = Low, data passes from B-port to A-port; when DIR = High, data flows from A-port to B-port. No external latches or clocking are needed-the device performs level-sensitive, combinatorial bus translation in real time.
What is the guaranteed low-level output voltage (VOL) for SN74AS645DWE4 at full load?
At IOL = 48 mA and VCC = 4.5 V, SN74AS645DWE4 guarantees VOL ≤ 0.55 V per the electrical characteristics table in the SDAS278 datasheet. This specification ensures reliable logic-low recognition across cascaded TTL loads and accounts for worst-case process, voltage, and temperature corners.
Is SN74AS645DWE4 pin-compatible with SN74ALS645A series devices?
Yes, SN74AS645DWE4 shares identical pinout, package dimensions, and terminal functions with SN74ALS645A variants in the SOIC-20 (DW) package. Both families use the same 20-pin assignment for DIR, OE, A1–A8, B1–B8, VCC, and GND-enabling mechanical interchangeability, though electrical parameters (speed, drive, power) differ.
What is the purpose of the OE (output enable) pin on SN74AS645DWE4?
The OE pin on SN74AS645DWE4 controls 3-state output activation: when OE = Low, the transceiver drives A and B ports according to DIR state; when OE = High, all A and B outputs enter high-impedance state-electrically isolating both buses. This enables multi-master arbitration, bus sharing, and safe hot-insertion in live systems.
SN74AS645DWE4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AS
- Package/Case:
- 20-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, 64mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SOIC
SN74AS645DWE4 FAQ
1.How can I place an order for SN74AS645DWE4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AS645DWE4 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 SN74AS645DWE4 reliable?
The price and inventory of SN74AS645DWE4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AS645DWE4 is usually 5 days.
3.What payment methods are accepted for SN74AS645DWE4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AS645DWE4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74AS645DWE4?
SN74AS645DWE4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AS645DWE4 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 SN74AS645DWE4?
For technical support, including SN74AS645DWE4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AS645DWE4 requirements.
6.How does Aetrix verify that SN74AS645DWE4 is sourced from the original manufacturer or authorized distributors?
All SN74AS645DWE4 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 SN74AS645DWE4 meets industry standards.
7.What is the process for return or replacement of SN74AS645DWE4?
All SN74AS645DWE4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74AS645DWE4, 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 SN74AS645DWE4 part is unused and in its original packaging.
Return procedure for SN74AS645DWE4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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