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Texas Instruments SN74ALS645A-1DWR
- Part No.:
- SN74ALS645A-1DWR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS645A-1DWR.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,339
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Product details
Overview
SN74ALS645A-1DWR 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 transfer 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. It is used in legacy industrial backplane interfaces requiring isolated bus communication.
For engineers reviewing the SN74ALS645A-1DWR datasheet, SN74ALS645A-1DWR pinout, SN74ALS645A-1DWR application, or SN74ALS645A-1DWR equivalent, this page delivers verified electrical specs, functional truth table, package dimensions, real-world use cases, and validated alternative parts - all grounded in TI's SDAS278 datasheet and official packaging documentation.
Technical Context
The SN74ALS645A-1DWR implements true bipolar ALS logic with dual 8-bit bidirectional data paths controlled by DIR and OE inputs. Its 3-state outputs support bus isolation when OE is high, and direction reversal (A→B or B→A) based on DIR level - enabling flexible data routing without external logic.
It operates at VCC = 4.5–5.5 V with guaranteed VOL ≤ 0.5 V at IOL = 48 mA and VOH ≥ 2.4 V at IOH = –12 mA. Propagation delays are specified from 1 ns (tPLH min) to 10 ns (tPHL max) under CL = 50 pF, supporting reliable timing in synchronous and asynchronous bus systems.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - ensures compatibility with standard 5 V TTL/ALS power rails and noise margin stability. |
| IOL (max) | 48 mA - enables direct driving of multiple TTL loads or moderate-current bus stubs without external buffers. |
| tPHL / tPLH | 3 ns to 10 ns - supports bus speeds up to ~100 MHz in short-line, low-capacitance configurations. |
| Operating Temp | 0°C to 70°C - qualified for commercial-grade embedded and industrial control applications. |
| Package | SOIC-20 (DW) - surface-mount, RoHS-compliant, MSL Level-1, 2.65 mm max height, 12.8 mm × 7.5 mm footprint. |
| Logic Family | Advanced Low-Power Schottky (ALS) - provides lower power than standard LS while retaining speed and drive strength. |
| Output Type | 3-state (high-impedance) - allows multiple devices to share a common bus without contention. |
Pinout & Package
SN74ALS645A-1DWR uses a 20-pin SOIC (DW) package per TI drawing DW0020A: 12.8 mm × 7.5 mm body, 1.27 mm pitch, 2.65 mm max height, gull-wing leads. Pin 1 is marked via notch and located in Quadrant Q1 per tape-and-reel specification.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | DIR | Direction control input: LOW enables B→A data flow; HIGH enables A→B data flow. |
| 2–9 | A1–A8 | Input/output port A - connects to first data bus; bidirectional when enabled. |
| 10 | GND | Ground reference for logic and power return path. |
| 11–18 | B1–B8 | Input/output port B - connects to second data bus; bidirectional when enabled. |
| 19 | OE | Output enable active-low: LOW enables transceiver; HIGH forces all A/B pins into high-impedance state. |
| 20 | VCC | Positive supply input: must be decoupled locally with 0.1 µF ceramic capacitor. |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional Data Flow | Single DIR pin selects A→B or B→A path - eliminates need for separate transmit/receive lines or multiplexing logic. |
| High-Drive 3-State Outputs | 48 mA sink capability supports fan-out to ≥10 standard TTL loads - reduces need for bus repeaters in mid-length traces. |
| TTL-Compatible Interface | VIH = 2 V, VIL = 0.8 V, VOH ≥ 2.4 V, VOL ≤ 0.5 V - ensures interoperability with legacy 5 V logic families including LS, S, and AS. |
| Low Propagation Delay | Typical tPLH/tPHL < 5 ns - enables use in high-speed address/data multiplexing and memory bus expansion. |
| Isolation Control | OE pin disables both A and B ports simultaneously - prevents bus contention during reset, power-up, or fault conditions. |
Applications
| Industrial Backplane Interface | Legacy System Bus Expansion |
|---|---|
Use Scenario: Interfacing microcontroller local bus to a multi-slot ISA-style backplane carrying parallel I/O and memory-mapped peripherals. IC Role / Device Role: Bidirectional data bridge isolating CPU bus from shared backplane during arbitration cycles. Use Value: Enables hot-swap-safe bus segmentation using OE control, while DIR allows dynamic master/slave role switching between slots. |
Use Scenario: Adding a second 8-bit peripheral interface to an aging 8051-based controller where PCB space prohibits adding discrete buffers. IC Role / Device Role: Octal transceiver extending data bus width between MCU and external ADC/DAC or display driver. Use Value: Delivers 48 mA drive per line - sufficient to drive long traces and multiple CMOS/TTL inputs without signal degradation. |
| Test Equipment Data Routing | Programmable Logic Interface |
Use Scenario: Reconfigurable signal path in automated test equipment (ATE) switching between DUT data bus and pattern generator/analyzer ports. IC Role / Device Role: Directionally controlled bus switch enabling bidirectional stimulus/response capture on same physical lines. Use Value: DIR and OE allow precise timing-controlled bus handover - critical for glitch-free transitions during test vector execution. |
Use Scenario: Glue logic between CPLD/FPGA I/O banks and external 5 V logic subsystems (e.g., legacy sensors or displays). IC Role / Device Role: Level-shifting and bus-isolating transceiver ensuring safe interfacing despite voltage domain mismatches. Use Value: ALS family's low input current (±0.1 mA) minimizes loading on FPGA I/O pins, preserving timing margins. |
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 | No -1 suffix: rated IOL = 24 mA (not 48 mA); otherwise identical pinout, timing, and logic behavior. | Suitable only where bus load is light (< 5 TTL units) or trace capacitance is minimal. | Select SN74ALS645ADWR only if drive strength requirements are lower and cost optimization is prioritized. |
| SN74AS645N | AS family: faster propagation (min tPLH = 2 ns), higher IOL = 64 mA, but higher ICC (up to 149 mA) and tighter VIH/VIL thresholds (VIH = 2 V, VIL = 0.8 V). | Better for high-speed timing-critical designs; less tolerant of marginal input noise or degraded signal integrity. | Choose SN74AS645N when sub-10 ns timing budgets exist and power consumption is secondary to speed. |
Compared with SN74ALS645ADWR and SN74AS645N, the SN74ALS645A-1DWR uniquely balances robust 48 mA drive, ALS power efficiency (~55 mA ICC active), and proven noise immunity - making it optimal for industrial bus interfaces where reliability trumps peak speed.
Availability
SN74ALS645A-1DWR is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus expansion, test equipment data routing, and programmable logic interface applications requiring stable component supply across extended production lifecycles.
Supply support for SN74ALS645A-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 deep heritage in military- and industrial-grade components.
The SN74ALS645A-1DWR belongs to TI's legacy ALS logic product line, engineered for high-reliability 5 V digital systems where noise immunity, consistent drive strength, and long-term availability are critical.
FAQ
What is the maximum recommended output current for SN74ALS645A-1DWR?
The SN74ALS645A-1DWR is rated for a maximum low-level output current (IOL) of 48 mA per pin when VCC is between 4.75 V and 5.25 V. This is its defining "-1" feature - distinguishing it from the standard SN74ALS645A (24 mA). Exceeding this value risks VOL degradation or thermal stress. The SN74ALS645A-1DWR datasheet specifies VOL ≤ 0.5 V under this condition.
Does SN74ALS645A-1DWR support hot-swapping on a live bus?
SN74ALS645A-1DWR does not include built-in hot-swap protection circuitry. However, its 3-state outputs and fast disable timing (tPLZ ≤ 15 ns) allow controlled bus isolation via OE assertion before insertion/removal. Safe hot-swap requires external current-limiting and sequencing - the SN74ALS645A-1DWR itself provides the necessary high-impedance state but no fault detection or slew-rate control.
Can SN74ALS645A-1DWR interface directly with 3.3 V logic?
No - SN74ALS645A-1DWR is a 5 V-only device with VIH = 2.0 V minimum and VIL = 0.8 V maximum. Driving its inputs from 3.3 V logic may cause unreliable HIGH recognition due to insufficient noise margin. Likewise, its 5 V outputs exceed 3.3 V I/O absolute maximum ratings. Level translation (e.g., TXB0108) is required for 3.3 V system interfacing. The SN74ALS645A-1DWR must operate at VCC = 4.5–5.5 V.
What is the function of the DIR pin on SN74ALS645A-1DWR?
The DIR (direction) pin on SN74ALS645A-1DWR controls data flow direction: when DIR = LOW, data passes from B-bus to A-bus; when DIR = HIGH, data passes from A-bus to B-bus. It operates independently of OE - DIR sets path polarity, while OE enables/disables the entire transceiver. This dual-control architecture allows dynamic bus role reversal in systems like master/slave arbitration. The SN74ALS645A-1DWR truth table confirms this behavior.
Is SN74ALS645A-1DWR pin-compatible with SN74LS645?
Yes - SN74ALS645A-1DWR is functionally and pin-compatible with SN74LS645 and SN74ALS645A, sharing identical 20-pin SOIC (DW) pinout, logic diagram, and terminal functions (DIR, OE, A1–A8, B1–B8, VCC, GND). However, SN74ALS645A-1DWR offers improved speed (10 ns vs. 15 ns max tPHL), lower power, and higher drive (48 mA vs. 24 mA for LS), making it a direct performance upgrade. No PCB changes are required for replacement.
SN74ALS645A-1DWR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- 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-1DWR FAQ
1.How can I place an order for SN74ALS645A-1DWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS645A-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 SN74ALS645A-1DWR reliable?
The price and inventory of SN74ALS645A-1DWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS645A-1DWR is usually 5 days.
3.What payment methods are accepted for SN74ALS645A-1DWR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS645A-1DWR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS645A-1DWR?
SN74ALS645A-1DWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS645A-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 SN74ALS645A-1DWR?
For technical support, including SN74ALS645A-1DWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS645A-1DWR requirements.
6.How does Aetrix verify that SN74ALS645A-1DWR is sourced from the original manufacturer or authorized distributors?
All SN74ALS645A-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 SN74ALS645A-1DWR meets industry standards.
7.What is the process for return or replacement of SN74ALS645A-1DWR?
All SN74ALS645A-1DWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS645A-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 SN74ALS645A-1DWR part is unused and in its original packaging.
Return procedure for SN74ALS645A-1DWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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