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Texas Instruments SN74LS645-1DW
- Part No.:
- SN74LS645-1DW
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74LS645-1DW.pdf
- Description:
- IC TXRX NON-INVERT 5.25V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,367
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Product details
Overview
SN74LS645-1DW from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for bidirectional data flow control in TTL-level digital systems. It features 8-bit non-inverting data paths, independent output-enable (OE) and direction (DIR) controls, and operates over 0°C to 70°C. Used in legacy industrial controllers and backplane interface modules where level-shifting and bus isolation are required.
For engineers reviewing the SN74LS645-1DW datasheet, SN74LS645-1DW pinout, SN74LS645-1DW application, or SN74LS645-1DW equivalent, key selection considerations include its SOIC-20 package, TTL-compatible input thresholds, 3-state output drive capability, and compatibility with LS-family timing and loading specifications.
Technical Context
This device implements dual 8-bit bidirectional buffers with separate DIR (direction) and OE (output enable) inputs, enabling synchronous control of data flow between two buses. Each data line supports true TTL input levels and delivers standard LS output drive (IOH = –15 mA, IOL = 24 mA at VCC = 5 V).
Propagation delay is specified at tPLH/tPHL ≤ 25 ns (max) under typical load conditions, and it maintains full compatibility with SN74LS640/645 family logic thresholds and fan-out rules. No internal latching or clocking is present - operation is purely combinational and level-sensitive.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Octal 3-state bidirectional bus transceiver - enables isolated, controlled data transfer between two 8-bit buses |
| Logic Family | TTL LS - compatible with standard 5-V TTL voltage levels and noise margins |
| Supply Voltage | VCC = 4.75 V to 5.25 V - requires regulated 5-V rail; no internal regulation |
| Output Drive | IOL = 24 mA / IOH = –15 mA - sufficient to drive 20 LS loads or one ALS load |
| Propagation Delay | tPD ≤ 25 ns (max) - supports synchronous bus rates up to ~20 MHz in minimal-load configurations |
| Operating Temperature | 0°C to +70°C - commercial-grade rating; not rated for extended or military temperature ranges |
| Package | SOIC-20 (DW) - 7.5-mm body width, 1.27-mm pitch, surface-mount compatible |
Pinout & Package
SN74LS645-1DW is housed in a 20-pin small-outline integrated circuit (SOIC) package with 1.27-mm lead pitch and 7.5-mm body width. The package conforms to JEDEC MS-013 and supports standard reflow profiles (Level-1-260°C-UNLIM).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction control input | High = A→B data flow; Low = B→A; determines signal path polarity |
| 2–9 (A1–A8) | Bus A data terminals | Input when DIR = Low and OE = Low; output when DIR = High and OE = Low |
| 10 (GND) | Ground reference | Primary return path for all logic and output currents |
| 11–18 (B1–B8) | Bus B data terminals | Input when DIR = High and OE = Low; output when DIR = Low and OE = Low |
| 19 (OE) | Output enable input | Low = 3-state outputs active; High = all outputs high-impedance |
| 20 (VCC) | Power supply | 5-V nominal supply; decoupling capacitor required within 1 cm of pin |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional data control | Single DIR pin selects real-time A→B or B→A flow without latch or clock dependency |
| Independent 3-state enable | Dedicated OE pin disables both A and B ports simultaneously into high-impedance state |
| TTL-compatible interface | Meets LS-series VIH/VIL thresholds (2.0 V/0.8 V), ensuring interoperability with legacy 74LS logic |
| SOIC-20 footprint | Standardized 7.5-mm wide package enables drop-in replacement in existing LS-based PCB layouts |
| Commercial temperature range | Validated operation from 0°C to +70°C supports deployment in office, lab, and non-harsh industrial environments |
Applications
| Industrial Backplane Interface | Legacy System Bus Isolation |
|---|---|
Use Scenario: Interfacing microprocessor local bus to peripheral expansion backplane in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional buffer isolating CPU address/data bus from modular I/O cards while maintaining TTL timing integrity. Use Value: Prevents bus contention during hot-swap events and allows independent enable/disable of each expansion slot via OE control. | Use Scenario: Replacing failed SN74LS245 units in aging test equipment where board space and pinout must be preserved. IC Role / Device Role / Timing Role: Pin-compatible octal transceiver providing identical propagation delay and drive strength as original design. Use Value: Maintains system timing budget without requiring layout modification or firmware update. |
| Microcontroller Peripheral Expansion | Parallel Printer Port Buffering |
Use Scenario: Extending GPIO count of 8-bit microcontrollers (e.g., 8051 derivatives) to drive external memory or display modules. IC Role / Device Role / Timing Role: Level-translating and current-boosting interface between MCU port and high-capacitance parallel bus. Use Value: Enables reliable 8-bit data transfers at 2–5 MHz without signal degradation or timing violation. | Use Scenario: Isolating host parallel port signals (STROBE, ACK, BUSY) from printer-side capacitance and noise in embedded print subsystems. IC Role / Device Role / Timing Role: Unidirectional or bidirectional signal conditioner for Centronics-style parallel interfaces. Use Value: Eliminates ground loop issues and improves noise immunity on long cable runs using controlled 3-state output transitions. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS245N | Same 20-pin PDIP package; identical electrical specs but lacks -1 suffix variant marking; obsolete in SOIC form | Requires through-hole assembly; not suitable for new SOIC-based designs | Select only if legacy PDIP layout reuse is mandatory and thermal/mounting constraints allow |
| SN74LS645-1DWR | Same die and specs; tape-and-reel packaging (2000 pcs), RoHS-compliant NiPdAu finish, MSL Level-1 | Designed for automated SMT production; supports high-volume pick-and-place | Preferred for new designs requiring volume manufacturing and modern compliance requirements |
Compared with SN74LS245N and SN74LS645-1DWR, the SN74LS645-1DW offers identical core functionality in an obsolete SOIC-20 format - ideal for repair or low-volume continuity builds where tape-and-reel logistics are unnecessary, but not recommended for new production due to discontinuation status.
Availability
SN74LS645-1DW is available at Aetrix Electronics and suitable for industrial backplane interface, legacy system bus isolation, and microcontroller peripheral expansion requiring stable component supply across long-lifecycle programs.
Supply support for SN74LS645-1DW 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 founded in 1930, specializing in analog, embedded processing, and logic solutions with broad industrial and automotive reach.
The SN74LS645 series belongs to TI's legacy TTL logic portfolio, engineered specifically for robust, deterministic bus interfacing in cost-sensitive, non-high-speed digital systems of the 1970s–1990s era.
FAQ
What is the function of the DIR pin on the SN74LS645-1DW?
The DIR (direction) pin on the SN74LS645-1DW controls data flow polarity: when DIR = HIGH, data passes from Bus A to Bus B; when DIR = LOW, data flows from Bus B to Bus A. This single-pin control eliminates need for separate transmit/receive lines and enables real-time bidirectional bus arbitration in the SN74LS645-1DW without external logic.
Is SN74LS645-1DW pin-compatible with SN74LS245?
Yes, SN74LS645-1DW is functionally and pinout-compatible with SN74LS245 in SOIC-20 package - both share identical pin assignments for DIR, OE, A/B buses, VCC, and GND. However, SN74LS645-1DW uses a -1 suffix denoting updated characterization; always verify timing margins in your specific SN74LS645-1DW application.
What is the maximum clock/data rate supported by SN74LS645-1DW?
The SN74LS645-1DW has no internal clock; its usable data rate depends on external system timing. With tPD ≤ 25 ns and setup/hold times under 15 ns, it reliably supports asynchronous bus cycles up to ~20 MHz in low-capacitance (<30 pF) environments. For higher rates, derate based on actual trace capacitance and termination in the SN74LS645-1DW implementation.
Does SN74LS645-1DW support 3.3-V operation?
No, SN74LS645-1DW is strictly a 5-V TTL device. Its input thresholds (VIH = 2.0 V min, VIL = 0.8 V max) and output drive characteristics are specified only for VCC = 4.75 V to 5.25 V. Operating SN74LS645-1DW at 3.3 V will result in undefined logic states and insufficient output swing; use a level-shifter or 3.3-V-compatible transceiver instead.
Why is SN74LS645-1DW marked as Obsolete in TI's packaging addendum?
TI classifies SN74LS645-1DW as Obsolete because it is no longer in active production - inventory is limited to remaining factory stock. TI continues to manufacture and support SN74LS645-1DWR (tape-and-reel) and SN74LS645-1N (PDIP), making SN74LS645-1DW suitable only for repair, spares, or legacy continuity, not new design starts.
SN74LS645-1DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Bulk
- 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, 48mA
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SOIC
SN74LS645-1DW FAQ
1.How can I place an order for SN74LS645-1DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS645-1DW 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 SN74LS645-1DW reliable?
The price and inventory of SN74LS645-1DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS645-1DW is usually 5 days.
3.What payment methods are accepted for SN74LS645-1DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS645-1DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS645-1DW?
SN74LS645-1DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS645-1DW 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 SN74LS645-1DW?
For technical support, including SN74LS645-1DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS645-1DW requirements.
6.How does Aetrix verify that SN74LS645-1DW is sourced from the original manufacturer or authorized distributors?
All SN74LS645-1DW 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 SN74LS645-1DW meets industry standards.
7.What is the process for return or replacement of SN74LS645-1DW?
All SN74LS645-1DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS645-1DW, 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 SN74LS645-1DW part is unused and in its original packaging.
Return procedure for SN74LS645-1DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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