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Texas Instruments SN74AS645DW
- Part No.:
- SN74AS645DW
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74AS645DW.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,706
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Product details
Overview
SN74AS645DW 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 SN74AS645DW datasheet, SN74AS645DW pinout, SN74AS645DW application, or SN74AS645DW equivalent, this page provides verified functional specifications, validated pin assignments, confirmed temperature and drive capability limits, and real-world use context for legacy TTL-compatible system integration.
Technical Context
The SN74AS645DW implements true bipolar TTL logic with active-high DIR and active-low OE controls, enabling deterministic A→B or B→A data flow without internal latching. Its 3-state outputs provide high-impedance isolation when OE is high, supporting shared-bus architectures.
It is characterized for 4.5 V–5.5 V VCC operation, exhibits propagation delays as low as 2 ns (tPHL/tPLH), and sustains 64 mA IOL at VCC = 4.5 V - a key differentiator from ALS variants - making it suitable for driving heavier capacitive loads in backplane or board-to-board interconnects.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - ensures compatibility with standard 5 V TTL power rails and tolerates supply ripple. |
| IOL (Low-level Output) | 64 mA - enables direct drive of multiple TTL inputs or moderate PCB trace capacitance without external buffers. |
| tPLH / tPHL | 2 ns min / 9.5 ns max - supports high-speed bus arbitration in real-time control subsystems. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded systems, not extended or military range. |
| Logic Family | AS (Advanced Schottky) - delivers higher speed and lower power than standard LS, with compatible input thresholds. |
| Output Type | 3-State (active-low OE) - allows dynamic bus sharing and prevents contention during multi-master operations. |
| Pin Count & Package | 20-pin SOIC (DW) - surface-mount footprint with 1.27 mm pitch, compatible with automated assembly and IPC-7351 land patterns. |
Pinout & Package
SN74AS645DW uses a 20-pin SOIC (DW) package with 7.5 mm width, 12.8 mm length, and maximum height of 2.65 mm per JEDEC MS-013. Pin 1 is located at the top-left corner with beveled edge marking.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | High = A→B data flow; Low = B→A data flow - determines bus transmission direction synchronously. |
| 2–9 (A1–A8) | Port A I/O Terminals | Bidirectional data lines connected to one bus segment; high-impedance when OE high or DIR inactive. |
| 10 (GND) | Ground Reference | Primary signal return path; must be low-inductance connection to minimize switching noise. |
| 11–18 (B1–B8) | Port B I/O Terminals | Bidirectional data lines connected to second bus segment; functionally mirrored to A-side under DIR control. |
| 19 (OE) | Output Enable Input | Active-low - drives all A/B outputs into high-impedance state when high, isolating both buses. |
| 20 (VCC) | Power Supply | +5 V supply pin; requires local 0.1 µF ceramic decoupling adjacent to pin for stable high-speed operation. |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional Bus Interface | Enables single-device replacement of dual unidirectional transceivers, reducing component count and PCB area in bus repeater designs. |
| 64 mA Sink Capability | Supports fan-out to ≥20 standard TTL loads or direct termination of unterminated stubs in parallel bus topologies. |
| Sub-10 ns Propagation Delay | Meets timing budgets for 25+ MHz bus clocking in legacy industrial controllers and test equipment interfaces. |
| True 3-State Outputs | Guarantees no DC path between A and B ports during disable, preventing bus contention and latch-up in hot-swap scenarios. |
| SOIC-20 Surface-Mount Package | Enables reflow-compatible assembly and meets IPC Class 2 reliability requirements for long-lifecycle industrial hardware. |
Applications
| Industrial PLC Backplanes | Legacy Computer Memory Expansion |
|---|---|
Use Scenario: Isolating and extending parallel address/data buses between CPU and I/O modules in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional bus transceiver managing synchronous A→B or B→A transfers under DIR control, with OE enabling module hot-swap capability. Use Value: Eliminates need for discrete direction logic and dual transceivers, reducing BOM cost and improving signal integrity on 20 cm backplane traces. | Use Scenario: Interfacing ISA-bus expansion cards with motherboard resources in retro-computing or diagnostic test systems. IC Role / Device Role / Timing Role: Level-shifting and bus-driving transceiver handling 8-bit data paths between legacy peripherals and host controllers. Use Value: 64 mA IOL ensures reliable low-voltage transitions across noisy ISA slots, while sub-10 ns delay preserves setup/hold timing margins. |
| Test Equipment Signal Routing | Avionics Data Concentrators |
Use Scenario: Dynamic reconfiguration of stimulus/response paths in automated test equipment using multiplexed digital I/O banks. IC Role / Device Role / Timing Role: Controlled bus switch enabling on-the-fly routing of DUT signals to measurement or generation channels via DIR/OE sequencing. Use Value: 3-state isolation prevents signal leakage between test domains, and fast enable/disable times (<13 ns) support high-throughput test sequences. | Use Scenario: Aggregating sensor data from multiple ARINC 429 receiver front-ends onto a centralized processing bus in legacy avionics units. IC Role / Device Role / Timing Role: Synchronized bus repeater translating isolated serial receiver outputs into parallel format for microcontroller ingestion. Use Value: AS-family speed and noise immunity ensure robust operation in EMI-prone aircraft environments, while commercial temp grade meets line-replaceable unit (LRU) requirements. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bidirectional bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS645ADWR | ALS family: lower IOL (24 mA), slower tPHL/tPLH (up to 10 ns), same pinout and voltage specs. | Suitable only for low-fanout, lower-speed legacy systems where power efficiency outweighs speed. | Select SN74ALS645ADWR only if design operates below 10 MHz and load capacitance ≤30 pF per line. |
| 74F645SC | F-family: 50 mA IOL, 8 ns max tPLH/tPHL, identical 20-pin SOIC package and logic function. | Requires tighter VCC regulation (4.75–5.25 V) and has higher ICC (97 mA vs. 95 mA for SN74AS645DW). | Choose 74F645SC when migrating from F-series designs; verify power delivery margin due to higher quiescent current. |
Compared with SN74ALS645ADWR and 74F645SC, the SN74AS645DW delivers superior drive strength and speed within the same SOIC-20 footprint, making it optimal for noise-immune, high-fanout bus extension where timing closure is critical.
Availability
SN74AS645DW is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy computer memory expansion, and test equipment signal routing requiring stable component supply over extended production lifecycles.
Supply support for SN74AS645DW 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic ICs for industrial, automotive, and communications markets.
The SN74AS645DW belongs to TI's legacy 74AS logic family, engineered for high-speed, low-power TTL-compatible bus interfacing in mission-critical industrial and test systems.
FAQ
What is the maximum operating temperature range for the SN74AS645DW?
The SN74AS645DW is characterized for operation from 0°C to 70°C, consistent with commercial-grade specifications. It is not rated for extended temperature ranges such as –40°C to 125°C or military-grade –55°C to 125°C. Designs requiring wider thermal margins must select SN54AS645 variants in CDIP or CFP packages instead of the DW SOIC variant.
Does the SN74AS645DW support 3.3 V logic levels?
No, the SN74AS645DW is a 5 V-only device with TTL-compatible input thresholds (VIH = 2 V min, VIL = 0.8 V max) and requires VCC between 4.5 V and 5.5 V. It does not tolerate 3.3 V supply or interface directly with LVCMOS logic without level translation, as its inputs are not 5 V tolerant in 3.3 V systems and outputs swing rail-to-rail around 5 V.
What is the purpose of the DIR and OE pins on the SN74AS645DW?
The DIR (pin 1) input controls data direction: DIR = high enables A→B transfer; DIR = low enables B→A transfer. The OE (pin 19) input is active-low and disables all outputs into high-impedance state when asserted high, electrically isolating both A and B buses. Both controls operate asynchronously and independently, allowing flexible bus arbitration schemes in multi-master systems.
Can the SN74AS645DW replace the SN74ALS645A in an existing design?
Yes, the SN74AS645DW is pin-compatible and functionally equivalent to the SN74ALS645A in SOIC-20 (DW) packaging, but offers higher performance: 64 mA vs. 24 mA IOL and faster propagation delays (9.5 ns vs. 10 ns max). However, verify that the increased drive strength does not cause overshoot on lightly loaded lines, and confirm power delivery can support higher ICC (95 mA vs. 55 mA).
Is the SN74AS645DW RoHS compliant?
Yes, the SN74AS645DW is RoHS compliant with lead finish NIPDAU (Nickel/Palladium/Gold), per TI's packaging documentation. It carries MSL Level-1 rating (unlimited floor life at ≤30°C/60% RH) and is supplied in 2000-piece tape-and-reel format (SN74AS645DWR), meeting modern environmental and assembly requirements for industrial manufacturing.
SN74AS645DW 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
SN74AS645DW FAQ
1.How can I place an order for SN74AS645DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AS645DW 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 SN74AS645DW reliable?
The price and inventory of SN74AS645DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AS645DW is usually 5 days.
3.What payment methods are accepted for SN74AS645DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AS645DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74AS645DW?
SN74AS645DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AS645DW 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 SN74AS645DW?
For technical support, including SN74AS645DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AS645DW requirements.
6.How does Aetrix verify that SN74AS645DW is sourced from the original manufacturer or authorized distributors?
All SN74AS645DW 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 SN74AS645DW meets industry standards.
7.What is the process for return or replacement of SN74AS645DW?
All SN74AS645DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74AS645DW, 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 SN74AS645DW part is unused and in its original packaging.
Return procedure for SN74AS645DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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