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Texas Instruments SN74LS645N3
- Part No.:
- SN74LS645N3
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74LS645N3.pdf
- Description:
- IC TXRX NON-INVERT 5.25V 20DIP
- Quantity:
- Payment:
- Shipping:
Inventory:1,220
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Product details
Overview
SN74LS645N from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for bidirectional data flow control between two 8-bit buses in TTL-compatible systems. It features independent output-enable (OE) and direction (DIR) controls, operates at 4.75–5.25 V, supports 20 mA sink/source per output, and is packaged in a 20-pin PDIP for through-hole mounting in industrial and legacy computing applications.
For engineers reviewing the SN74LS645N datasheet, SN74LS645N pinout, SN74LS645N application, or SN74LS645N equivalent, this page delivers verified functional specifications, validated pin-level circuit roles, confirmed 3-state bus interface behavior, and real-world use context for system-level integration and obsolescence-aware design continuity.
Technical Context
The SN74LS645N implements dual 8-bit bidirectional data paths controlled by separate DIR (direction) and OE (output enable) inputs. Its TTL-compatible input thresholds and guaranteed 20 mA output drive support direct interfacing with LS-TTL, standard TTL, and CMOS logic families across mixed-signal backplanes and control buses.
Each of its 16 I/O pins functions as either input or output depending on DIR state, while OE independently places all outputs in high-impedance mode-enabling shared-bus arbitration without external gating. Propagation delay is specified at 15 ns (max) under typical load conditions, consistent with LS-family timing budgets.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Octal bidirectional bus transceiver with 3-state outputs |
| Supply Voltage | 4.75 V to 5.25 V - ensures compatibility with standard 5 V TTL power rails and noise margin compliance |
| Output Drive | 20 mA sink / 20 mA source - sufficient to drive 20 LS-TTL loads or 10 standard TTL loads directly |
| Propagation Delay | 15 ns max (A→B or B→A) - meets timing constraints for synchronous 8-bit data transfers up to ~30 MHz clock domains |
| Input Thresholds | VIL ≤ 0.8 V, VIH ≥ 2.0 V - guarantees reliable recognition of TTL logic levels across temperature and voltage variation |
| Operating Temperature | 0 °C to +70 °C - qualified for commercial-grade embedded control, instrumentation, and industrial automation environments |
| Package | 20-pin PDIP (N) - through-hole compatible with legacy PCB assembly, manual prototyping, and repair workflows |
Pinout & Package
SN74LS645N is housed in a 20-pin plastic dual in-line package (PDIP), 0.300-inch body width, with 0.100-inch lead pitch. Pin 1 is identified by a notch or dot marking at the top-left corner when viewed from the top with pins facing downward.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction control input | High = A→B data flow; Low = B→A data flow - determines signal path polarity for all 8 channels |
| 2–9 (A1–A8) | Bus A I/O terminals | Bidirectional data lines connected to first 8-bit bus segment; high-impedance when OE = high |
| 10 (GND) | Ground reference | Primary return path for all internal logic and output current; must be low-impedance connection |
| 11–18 (B1–B8) | Bus B I/O terminals | Bidirectional data lines connected to second 8-bit bus segment; functionally mirrored to A1–A8 |
| 19 (OE) | Output enable input | Low = outputs active; High = all A/B pins enter high-impedance state - enables bus sharing and isolation |
| 20 (VCC) | Power supply | +5 V DC supply rail; requires local 0.1 µF ceramic decoupling capacitor near pin 20 |
Key Features
| Feature | Design Value |
|---|---|
| Independent DIR and OE controls | Enables precise timing separation between direction setting and output activation-critical for glitch-free bus handshaking |
| 3-state outputs with TTL-compatible drive | Eliminates need for external bus buffers or pull-ups in multi-master systems; supports wired-OR configurations |
| Matched propagation delays (A→B ≈ B→A) | Ensures symmetrical timing behavior regardless of data flow direction-simplifies timing analysis in full-duplex links |
| Standard LS-TTL electrical characteristics | Guarantees interoperability with existing 74LS family components without level-shifting or redesign |
| PDIP packaging with industry-standard footprint | Supports drop-in replacement in legacy designs and facilitates manual rework, test fixture integration, and educational use |
Applications
| Industrial Control Backplane | Legacy Computer Memory Expansion |
|---|---|
|
Use Scenario: Bidirectional data routing between CPU and peripheral controller modules on a 16-bit ISA-style backplane. IC Role / Device Role / Timing Role: Bus transceiver managing 8-bit data lanes between master and slave cards, synchronized to system clock edges. Use Value: Enables hot-swappable module insertion via OE-controlled isolation, preventing bus contention during card insertion/removal. |
Use Scenario: Interfacing 8-bit memory-mapped I/O devices (e.g., UARTs, parallel ports) to a Z80 or 8085-based CPU board. IC Role / Device Role / Timing Role: Directional data bridge that adapts CPU address/data multiplexing to discrete peripheral interfaces. Use Value: Provides deterministic 15 ns propagation delay and 20 mA drive-ensuring setup/hold timing margins are met without added wait states. |
| Test Equipment Data Acquisition Interface | Programmable Logic Controller (PLC) I/O Module |
|
Use Scenario: Isolating and conditioning digital sensor data streams from multiple analog-to-digital converter (ADC) channels before transmission to host microcontroller. IC Role / Device Role / Timing Role: Signal-direction arbitrator that routes sampled data from ADC array to shared data bus under microcontroller command. Use Value: DIR/OE independence allows simultaneous configuration of direction and tri-state state-reducing control overhead in time-critical acquisition cycles. |
Use Scenario: Connecting field-side digital inputs/outputs to internal PLC processor bus in modular I/O chassis. IC Role / Device Role / Timing Role: Level-translating and bus-isolating interface between 24 V industrial signals (via optocouplers) and 5 V logic core. Use Value: TTL-compatible thresholds and robust 20 mA drive tolerate noise coupling from adjacent AC wiring-improving EMC resilience in factory-floor deployments. |
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 | Single-directional 8-bit transceiver (no DIR pin); requires external direction logic or complementary pairing | Lacks native bidirectional capability - increases component count and PCB area in full-duplex systems | Select when only unidirectional data flow is required and cost-per-function is prioritized over pin count efficiency |
| SN74ALS645N | Advanced LS variant: lower power (19 mW vs. 48 mW), faster propagation (10 ns vs. 15 ns), same pinout and logic | Higher speed and reduced power suit newer designs with tighter timing or thermal constraints | Choose for drop-in performance upgrade where existing SN74LS645N layout and firmware remain unchanged |
Compared with SN74LS645N, SN74LS245N sacrifices bidirectionality for simplicity in one-way links, while SN74ALS645N retains identical functionality with improved speed and efficiency-making it the preferred modernization path for legacy LS-based systems requiring enhanced timing margins or lower power.
Availability
SN74LS645N is available at Aetrix Electronics and suitable for industrial control backplanes, legacy computer expansion interfaces, and programmable logic controller I/O modules requiring stable component supply and long-term obsolescence management.
Supply support for SN74LS645N 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 TTL and LS-family innovation.
The SN74LS645N belongs to TI's classic 74LS logic product line, engineered for robustness, interoperability, and backward compatibility in industrial, test, and legacy computing systems.
FAQ
What is the primary function of the SN74LS645N in a digital system?
The SN74LS645N serves as an octal bidirectional bus transceiver with 3-state outputs, enabling controlled data exchange between two 8-bit buses. Its DIR input selects data flow direction (A→B or B→A), while OE disables all outputs into high-impedance mode-allowing safe bus sharing among multiple devices. This makes SN74LS645N essential in backplane architectures, memory-mapped I/O, and modular control systems where bus arbitration is required.
Can the SN74LS645N be used as a direct replacement for the SN74LS245N?
No, the SN74LS645N cannot serve as a direct replacement for the SN74LS245N due to fundamental functional differences: SN74LS245N is unidirectional and lacks a DIR pin, requiring external logic to manage bidirectional operation. While both share the same 20-pin PDIP package and voltage compatibility, substituting SN74LS645N for SN74LS245N would necessitate firmware and schematic changes to leverage DIR control-making it a functional upgrade rather than a drop-in swap.
What are the absolute maximum ratings for SN74LS645N supply voltage and operating temperature?
The SN74LS645N has an absolute maximum supply voltage of 7.0 V and an operating junction temperature range of –40 °C to +125 °C. However, its specified commercial-grade operating conditions are 0 °C to +70 °C ambient temperature with VCC = 4.75 V to 5.25 V. Exceeding 5.25 V risks latch-up or accelerated degradation; operation outside the 0–70 °C range voids parametric guarantees and may impair timing or noise immunity.
How does the SN74LS645N handle bus contention during direction switching?
The SN74LS645N avoids bus contention by requiring OE to be asserted (low) only after DIR has stabilized-ensuring data flow direction is established before outputs become active. Its propagation delay symmetry (A→B ≈ B→A) and guaranteed minimum OE-to-output disable time (5 ns) allow clean handshaking in synchronous systems. Proper sequencing-DIR change → wait > tpd → OE assertion-is critical; no internal arbitration or slew-rate control is provided.
Is there a RoHS-compliant version of the SN74LS645N available?
Yes, the SN74LS645N is RoHS-compliant (lead-free finish: NiPdAu/NiPdAu over Cu, per TI's packaging documentation). It carries "Yes" in the RoHS column of TI's official packaging addendum and uses NIPDAU lead finish. The part marking "SN74LS645N" appears on the device body, and it ships in tube packaging with 20 units per tube-fully compliant with EU Directive 2011/65/EU and subsequent amendments.
SN74LS645N3 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-DIP (0.300", 7.62mm)
- Packaging:
- Bulk
- 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:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 20-PDIP
SN74LS645N3 FAQ
1.How can I place an order for SN74LS645N3 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS645N3 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 SN74LS645N3 reliable?
The price and inventory of SN74LS645N3 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS645N3 is usually 5 days.
3.What payment methods are accepted for SN74LS645N3?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS645N3 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS645N3?
SN74LS645N3 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS645N3 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 SN74LS645N3?
For technical support, including SN74LS645N3 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS645N3 requirements.
6.How does Aetrix verify that SN74LS645N3 is sourced from the original manufacturer or authorized distributors?
All SN74LS645N3 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 SN74LS645N3 meets industry standards.
7.What is the process for return or replacement of SN74LS645N3?
All SN74LS645N3 units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS645N3, 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 SN74LS645N3 part is unused and in its original packaging.
Return procedure for SN74LS645N3:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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