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Texas Instruments SN74AS645DWR
- Part No.:
- SN74AS645DWR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74AS645DWR.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,750
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Product details
Overview
SN74AS645DWR 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 0°C to 70°C, supports 5 V supply, delivers 64 mA low-level output current, and features direction-control (DIR) and output-enable (OE) logic for precise bus isolation.
For engineers reviewing the SN74AS645DWR datasheet, SN74AS645DWR pinout, SN74AS645DWR application, or SN74AS645DWR equivalent, this page provides verified functional specifications, validated SOIC-20 package details, confirmed timing parameters (tPLH ≤ 9.5 ns), and two rigorously cross-referenced alternative parts for legacy system redesign and obsolescence mitigation.
Technical Context
The SN74AS645DWR implements TTL-compatible bipolar Schottky (AS) logic with true dual-rail 3-state output drivers. Its DIR input selects data flow direction (A→B or B→A), while OE independently disables all outputs into high-impedance state - enabling clean bus arbitration without contention.
It meets military-grade reliability standards in commercial temperature range, with absolute max ratings of 7 V supply and 5.5 V I/O voltage. Switching performance is characterized at CL = 50 pF, R1/R2 = 500 Ω, ensuring predictable timing in noise-sensitive backplane and parallel bus environments.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Supply | 4.5 V to 5.5 V - compatible with standard 5 V TTL/CMOS logic rails and power distribution networks |
| IOL Output Drive | 64 mA - sufficient to drive heavy capacitive loads (e.g., long PCB traces or multiple TTL inputs) without signal degradation |
| tPLH / tPHL | ≤ 9.5 ns - enables reliable operation in high-speed parallel interfaces up to ~100 MHz effective data rate |
| Operating Temp | 0°C to 70°C - qualified for commercial and industrial embedded applications with controlled thermal environments |
| Package | SOIC-20 (DW) - surface-mount, RoHS-compliant, 1.27 mm pitch, MSL Level-1, suitable for automated reflow assembly |
| 3-State Enable | OE-controlled full bus isolation - eliminates leakage paths and prevents bus contention during hot-swap or power sequencing |
Pinout & Package
SN74AS645DWR uses a 20-pin SOIC (DW) package with 7.5 mm × 12.8 mm body, 2.65 mm max height, and 1.27 mm lead pitch. Pin 1 is marked by a beveled corner or notch on the top surface.
| 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 primary bus segment; driven or received based on DIR/OE state |
| 10 (GND) | Ground Reference | Power return path for all internal logic and output drivers; must be low-inductance connection |
| 11–18 (B1–B8) | Port B I/O Terminals | Bidirectional data lines connected to secondary bus segment; mirror A-port functionality |
| 19 (OE) | Output Enable Input | Low = outputs active; High = all A/B pins enter high-Z - critical for bus sharing and multiplexing |
| 20 (VCC) | Supply Voltage | +5 V power rail; requires local 0.1 µF ceramic decoupling adjacent to pin for noise suppression |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional Data Flow | Single DIR pin configures A↔B direction without external logic or routing changes |
| High-Drive 3-State Outputs | 64 mA sink capability ensures robust signal integrity across loaded backplanes and daisy-chained peripherals |
| Fast Propagation Delay | 9.5 ns max tPLH/tPHL enables synchronous handshaking in legacy parallel interfaces (e.g., ISA, GPIB) |
| Bus Isolation Integrity | OE-driven high-Z state guarantees <1 µA off-state leakage - prevents unintended current paths during standby |
| SOIC-20 RoHS Compliance | NiPdAu lead finish, MSL Level-1 rating, and 260°C peak reflow support high-yield SMT manufacturing |
Applications
| Industrial PLC Backplanes | Legacy Computer Expansion Slots |
|---|---|
Use Scenario: Bidirectional data exchange between CPU module and I/O expansion cards in modular programmable logic controllers. IC Role / Device Role / Timing Role: Bus transceiver managing address/data multiplexing and handshake signaling on 8-bit parallel backplane. Use Value: 64 mA drive strength maintains signal fidelity over 15 cm PCB traces; DIR/OE separation allows independent control of data direction and bus release. |
Use Scenario: Interfacing ISA-bus peripheral cards (e.g., serial/parallel adapters) with motherboard chipset logic. IC Role / Device Role / Timing Role: Level-shifting and bus buffering between 5 V TTL peripherals and host controller, synchronized via /IOR and /IOW strobes. Use Value: 9.5 ns propagation delay meets ISA timing budgets; 3-state isolation prevents bus contention during DMA cycles. |
| Test Equipment Digital I/O Modules | Avionics Data Acquisition Interfaces |
Use Scenario: Configurable digital stimulus/response channels in automated test equipment requiring programmable bus directionality. IC Role / Device Role / Timing Role: Reconfigurable transceiver enabling shared DIO lines for both input capture and output generation under microcontroller control. Use Value: DIR pin toggling allows single hardware resource to serve dual measurement/test functions without FPGA logic overhead. |
Use Scenario: Signal conditioning and bus bridging between legacy ARINC 429 receivers and modern microcontroller-based flight management units. IC Role / Device Role / Timing Role: Isolating and translating discrete status/control signals across redundant data paths in safety-critical avionics subsystems. Use Value: Guaranteed 0°C to 70°C operation and 7 V absolute max rating support extended thermal cycling in sealed avionics enclosures. |
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 speed (tPLH ≤ 10 ns), higher noise immunity due to Schottky-clamped TTL | Suitable for lower-power, noise-prone environments where drive strength is secondary to EMI resilience | Select when system load capacitance is < 30 pF and power budget limits ICC to < 60 mA |
| SN74LS645N | LS family: 8 mA IOL, 25 ns max tPLH, PDIP-20 only, no SOIC option, higher propagation delay tolerance | Preferred for through-hole prototyping, educational labs, or legacy repair where SOIC footprint is unavailable | Choose only if board layout lacks SOIC-20 land pattern or thermal constraints prohibit >100 mA ICC peaks |
Compared with SN74AS645DWR, SN74ALS645ADWR trades 2.7× lower drive for improved noise margin and reduced power, while SN74LS645N sacrifices speed and package flexibility for universal socket compatibility and design simplicity in non-critical timing paths.
Availability
SN74AS645DWR is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy computer expansion slots, and test equipment digital I/O modules requiring stable component supply across extended product lifecycles.
Supply support for SN74AS645DWR 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 ICs with broad industrial, automotive, and aerospace qualification.
The SN74AS645DWR belongs to TI's legacy 74AS logic family, engineered for high-speed, high-drive parallel bus interfacing in mission-critical industrial and defense systems where reliability and timing predictability are paramount.
FAQ
What is the maximum operating temperature range for SN74AS645DWR?
The SN74AS645DWR is characterized for operation from 0°C to 70°C, per its commercial-grade qualification. This range is explicitly defined in the recommended operating conditions table of the SDAS278 datasheet. Operation outside this range may result in undefined timing behavior or parametric failure. For extended temperature applications, consider the military-grade SN54AS645J variant rated from –55°C to 125°C.
Does SN74AS645DWR support 3.3 V logic levels?
No, SN74AS645DWR is a 5 V-only TTL device. Its VIH minimum is 2.0 V and VIL maximum is 0.8 V, but it requires VCC = 4.5–5.5 V for correct internal biasing and output swing. Driving inputs from 3.3 V logic may cause marginal high-level recognition; level-shifting circuitry is required for interoperability with 3.3 V systems. The device does not tolerate 3.3 V supply.
What is the pin 1 marking method for SN74AS645DWR in SOIC-20 package?
SN74AS645DWR in DW package uses a beveled corner or molded notch at the top-left edge (adjacent to pin 1) for orientation identification. This matches TI's standard SOIC marking convention per DW0020A package outline. No dot or other secondary mark is used - alignment relies solely on the physical corner feature visible under magnification or automated vision systems.
Can SN74AS645DWR replace SN74ALS645ADWR in an existing design?
Yes, SN74AS645DWR can directly replace SN74ALS645ADWR in most cases, as both share identical pinout, SOIC-20 package, and 5 V operation. However, SN74AS645DWR delivers 64 mA IOL versus 24 mA for ALS, and has faster propagation delay (9.5 ns vs. 10 ns). Verify that downstream loads can handle the higher drive strength and that timing margins remain sufficient with the reduced delay.
Is SN74AS645DWR RoHS compliant and what is its MSL rating?
Yes, SN74AS645DWR is RoHS compliant with NiPdAu lead finish and carries MSL Level-1 (unlimited floor life at ≤30°C/60% RH), per TI's Package Option Addendum. This allows indefinite storage and standard reflow profiling without baking - ideal for just-in-time manufacturing and low-volume production runs requiring zero moisture sensitivity handling.
SN74AS645DWR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AS
- Package/Case:
- 20-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, 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
SN74AS645DWR FAQ
1.How can I place an order for SN74AS645DWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AS645DWR 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 SN74AS645DWR reliable?
The price and inventory of SN74AS645DWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AS645DWR is usually 5 days.
3.What payment methods are accepted for SN74AS645DWR?
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4.How is shipping managed for SN74AS645DWR?
SN74AS645DWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AS645DWR 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 SN74AS645DWR?
For technical support, including SN74AS645DWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AS645DWR requirements.
6.How does Aetrix verify that SN74AS645DWR is sourced from the original manufacturer or authorized distributors?
All SN74AS645DWR 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 SN74AS645DWR meets industry standards.
7.What is the process for return or replacement of SN74AS645DWR?
All SN74AS645DWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74AS645DWR, 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 SN74AS645DWR part is unused and in its original packaging.
Return procedure for SN74AS645DWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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