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Texas Instruments SN74ALS645A-1DW
- Part No.:
- SN74ALS645A-1DW
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS645A-1DW.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:203
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Product details
Overview
SN74ALS645A-1DW from Texas Instruments is an octal bidirectional bus transceiver with 3-state outputs in a 20-pin SOIC (DW) package, designed for asynchronous two-way data communication between A and B buses. It features direction control (DIR), output enable (OE), ±48 mA low-level output drive (IOL), 0°C to 70°C operating range, and TTL-compatible logic levels.
For engineers reviewing the SN74ALS645A-1DW datasheet, SN74ALS645A-1DW pinout, SN74ALS645A-1DW application, or SN74ALS645A-1DW equivalent, this device supports legacy industrial backplane interfacing, microcontroller-to-peripheral data routing, and bus isolation in 5 V digital systems requiring robust drive strength and deterministic 3-state control.
Technical Context
The SN74ALS645A-1DW implements true TTL logic with asymmetric output drive: 48 mA sink capability at VO ≤ 0.5 V under VCC = 4.75–5.25 V, while sourcing only –12 mA at VO ≥ 2.4 V. Its propagation delays range from 3 ns to 10 ns (tPLH/tPHL) with 50 pF load, and enable/disable times (tPZH/tPLZ) are as low as 2 ns.
It uses dual active-low control inputs-DIR selects data flow direction (A→B or B→A), and OE places all outputs in high-impedance state. The device lacks internal clamping diodes on I/O ports, requiring external protection when interfacing with higher-voltage or noisy buses.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - Operates reliably across standard 5 V supply tolerances without regulation. |
| IOL (max) | 48 mA - Enables direct driving of multiple TTL loads or termination resistors on stubbed buses. |
| tPLH / tPHL | 3 ns to 10 ns - Supports >100 MHz bus toggle rates in point-to-point configurations with 50 pF load. |
| VOH / VOL | ≥2.4 V / ≤0.5 V - Guarantees noise margins >0.4 V for 5 V TTL and LVTTL interfaces. |
| Operating Temp | 0°C to 70°C - Qualified for commercial-grade embedded control and instrumentation applications. |
| Package | SOIC-20 (DW) - Surface-mount footprint compatible with automated assembly; 7.5 mm × 12.8 mm body. |
| Logic Family | ALS (Advanced Low-Power Schottky) - Delivers lower power than standard LS with comparable speed. |
Pinout & Package
SN74ALS645A-1DW is housed in a 20-pin SOIC (DW) package with 1.27 mm pitch, 2.65 mm max height, and RoHS-compliant NiPdAu lead finish (Level-1 MSL).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | Low = B→A data transfer; High = A→B data transfer; referenced to VCC/GND. |
| 2–9 (A1–A8) | Port A I/O Terminals | Bidirectional data lines connected to one bus segment; internally buffered with 3-state drivers. |
| 10 (GND) | Ground Reference | Primary signal return path; must be low-inductance connection for noise immunity. |
| 11–18 (B1–B8) | Port B I/O Terminals | Bidirectional data lines connected to second bus segment; electrically identical to A-side. |
| 19 (OE) | Output Enable Input | Active-low; forces all A/B pins into high-impedance state when high. |
| 20 (VCC) | Supply Voltage | +5 V nominal power rail; requires local 0.1 µF ceramic decoupling adjacent to pin. |
Key Features
| Feature | Design Value |
|---|---|
| 48 mA Sink Drive | Enables direct interface to unterminated 50 Ω transmission lines or multiple 74-series inputs without external buffers. |
| True TTL Input Thresholds | VIH = 2.0 V min, VIL = 0.8 V max - Ensures compatibility with legacy 5 V microcontrollers and peripheral ASICs. |
| Sub-10 ns Propagation Delay | Supports synchronous bus handshaking at up to 100 MHz clock rates in short-trace layouts. |
| 3-State Output Isolation | OE-controlled high-Z state prevents bus contention during DMA cycles or processor reset sequences. |
| ALS Logic Architecture | Reduces ICC to 36–60 mA (active) vs. 70+ mA in standard LS, lowering thermal load in dense PCB layouts. |
Applications
| Industrial Backplane Interface | Microcontroller Peripheral Expansion |
|---|---|
Use Scenario: Isolating CPU address/data bus from modular I/O cards in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional data bridge enabling read/write access to distributed analog/digital modules via shared parallel bus. Use Value: 48 mA drive sustains signal integrity across 15 cm backplane traces; 3-state control eliminates arbitration logic. |
Use Scenario: Extending GPIO count of an 8-bit MCU to drive LED arrays, relays, and sensors via parallel port. IC Role / Device Role / Timing Role: Level-shifting and bus-driving interface between MCU port and high-current peripherals. Use Value: DIR/OE pins allow software-configurable data direction and safe hot-plug disconnect without bus glitches. |
| Legacy System Bus Arbitration | Dual-Bus Memory Mapping |
Use Scenario: Sharing SRAM between two independent processors in a fault-tolerant avionics subsystem. IC Role / Device Role / Timing Role: Controlled bidirectional data conduit synchronized to each processor's bus cycle timing. Use Value: Sub-10 ns delays preserve setup/hold margins; OE gating enables atomic memory ownership handoff. |
Use Scenario: Mapping same physical RAM to different address windows for instruction and data fetch in Harvard-architecture DSPs. IC Role / Device Role / Timing Role: Directional data repeater isolating instruction and data buses while sharing memory resource. Use Value: Independent DIR control allows simultaneous read (A→B) and write (B→A) operations with no interlock overhead. |
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 | Standard version with 24 mA IOL (vs. 48 mA); otherwise identical pinout, timing, and logic behavior. | Suitable where lower drive strength suffices (e.g., short PCB traces, light loading); not recommended for long stubs or heavy capacitive loads. | Select SN74ALS645ADWR only if system-level testing confirms 24 mA meets VIH/VIL margin requirements under worst-case trace capacitance. |
| SN74AS645N | AS-family variant: faster tPLH/tPHL (2–9.5 ns), higher IOL (64 mA), but increased ICC (95–149 mA) and tighter VIH (2.0 V) requirement. | Better suited for high-speed timing-critical paths; incompatible with marginal 5 V supplies below 4.75 V due to AS input thresholds. | Choose SN74AS645N only when sub-9 ns propagation is mandatory and power budget permits +60% ICC increase over ALS variants. |
Compared with SN74ALS645A-1DW, SN74ALS645ADWR trades drive strength for lower power and cost, while SN74AS645N prioritizes speed and drive at the expense of power efficiency and supply tolerance-making SN74ALS645A-1DW the optimal balance for general-purpose 5 V bus isolation.
Availability
SN74ALS645A-1DW is available at Aetrix Electronics and suitable for industrial automation, legacy system upgrades, and embedded controller expansion requiring stable component supply, long-lifecycle support, and verified 5 V TTL interoperability.
Supply support for SN74ALS645A-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 specializing in analog, embedded processing, and logic solutions, with decades of heritage in TTL and advanced logic families.
The SN74ALS645A-1DW belongs to TI's legacy ALS logic portfolio, engineered for reliable 5 V bus interfacing in industrial and computing systems where deterministic timing and robust drive are critical.
FAQ
What is the maximum allowable IOL for SN74ALS645A-1DW and under what conditions?
The SN74ALS645A-1DW supports a maximum low-level output current (IOL) of 48 mA, but this rating applies exclusively when VCC is maintained between 4.75 V and 5.25 V. Outside this range, the device reverts to the standard 24 mA IOL limit per the SN74ALS645A specification. This condition is explicitly documented in the January 1995 SDAS278 datasheet, section "Recommended Operating Conditions".
Does SN74ALS645A-1DW have built-in ESD protection diodes on its I/O pins?
No, the SN74ALS645A-1DW does not integrate input or output ESD protection diodes. Its absolute maximum input voltage on I/O ports is limited to 5.5 V, and exceeding this-especially with fast transients-can cause latch-up or permanent damage. External TVS diodes or series resistors are required for robust operation in noisy industrial environments.
Can SN74ALS645A-1DW operate with a 3.3 V supply?
No, SN74ALS645A-1DW is not rated for 3.3 V operation. Its recommended VCC range is strictly 4.5 V to 5.5 V, and its input thresholds (VIH = 2.0 V, VIL = 0.8 V) are optimized for 5 V TTL signaling. Applying 3.3 V may result in undefined logic states, excessive ICC, or failure to meet VOL/VOH specifications.
What is the pin 1 marking and orientation for SN74ALS645A-1DW in tape-and-reel packaging?
SN74ALS645A-1DW uses Q1 quadrant orientation in tape-and-reel packaging, meaning pin 1 is located in the upper-left corner of the pocket when the reel is fed with the component facing upward and sprocket holes on the left edge. The part marking on the device body is "ALS645A-1", consistent across DW-packaged variants.
How does the -1 suffix in SN74ALS645A-1DW differ from the base SN74ALS645A?
The "-1" suffix denotes the enhanced-output version: SN74ALS645A-1DW guarantees 48 mA IOL (vs. 24 mA for non–1 versions), but only under tightly regulated VCC (4.75–5.25 V). All other electrical characteristics-including propagation delay, VOH/VOL, and pinout-are identical to the standard SN74ALS645A, and the -1 variant is not offered in military-grade (SN54) versions.
SN74ALS645A-1DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- 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, 24mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SOIC
SN74ALS645A-1DW FAQ
1.How can I place an order for SN74ALS645A-1DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS645A-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 SN74ALS645A-1DW reliable?
The price and inventory of SN74ALS645A-1DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS645A-1DW is usually 5 days.
3.What payment methods are accepted for SN74ALS645A-1DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS645A-1DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS645A-1DW?
SN74ALS645A-1DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS645A-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 SN74ALS645A-1DW?
For technical support, including SN74ALS645A-1DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS645A-1DW requirements.
6.How does Aetrix verify that SN74ALS645A-1DW is sourced from the original manufacturer or authorized distributors?
All SN74ALS645A-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 SN74ALS645A-1DW meets industry standards.
7.What is the process for return or replacement of SN74ALS645A-1DW?
All SN74ALS645A-1DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS645A-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 SN74ALS645A-1DW part is unused and in its original packaging.
Return procedure for SN74ALS645A-1DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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