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Texas Instruments SN74LS645-1N
- Part No.:
- SN74LS645-1N
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74LS645-1N.pdf
- Description:
- IC TXRX NON-INVERT 5.25V 20DIP
- Quantity:
- Payment:
- Shipping:
Inventory:304
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Product details
Overview
SN74LS645-1N from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for bidirectional data flow control in TTL-level parallel bus 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. It is used in legacy industrial controllers and backplane interface modules requiring level-shifted, isolated bus driving.
For engineers reviewing the SN74LS645-1N datasheet, SN74LS645-1N pinout, SN74LS645-1N application, or SN74LS645-1N equivalent, key selection criteria include its 3-state output drive capability, DIR/OE dual-control logic, PDIP-20 package compatibility with through-hole prototyping, and guaranteed TTL input thresholds across commercial temperature range.
Technical Context
The SN74LS645-1N implements two independent 4-bit bidirectional data paths within a single 20-pin PDIP package, each controlled by shared DIR and OE signals. Its output stage uses standard TTL totem-pole drivers with 3-state disable, enabling bus arbitration without external pull-ups or clamps.
Input thresholds are specified at VIL ≤ 0.8 V and VIH ≥ 2.0 V, ensuring robust noise margin against TTL-compatible sources. Propagation delay is characterized at tPLH/tPHL ≤ 25 ns (max) under VCC = 5 V, load = 15 pF, and RL = 400 Ω, supporting synchronous bus clocking up to ~15 MHz in constrained layouts.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Octal non-inverting bus transceiver with 3-state outputs |
| Supply Voltage | 4.75 V to 5.25 V - ensures compatibility with standard TTL power rails and noise immunity |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded control and instrumentation |
| Propagation Delay | ≤25 ns - supports reliable data transfer on 15-MHz synchronous buses with margin |
| Output Drive | IOH = –15 mA / IOL = 24 mA - sufficient to drive 10 standard TTL loads per output |
| Input Thresholds | VIL ≤ 0.8 V, VIH ≥ 2.0 V - guarantees clean logic recognition across voltage and temperature |
| Package | PDIP-20 (N), 0.300-inch width - compatible with legacy PCB footprints and manual soldering |
Pinout & Package
SN74LS645-1N is housed in a 20-pin plastic dual in-line package (PDIP-N) with 0.300-inch body width and standard 0.1-inch pin pitch. Pin 1 is marked by a notch or dot; pins are numbered counter-clockwise from pin 1.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | High = A→B data flow; Low = B→A - determines bus transfer direction |
| 2–9 (A1–A8) | Port A Data I/O | Bi-directional TTL-compatible data terminals for one bus segment |
| 10 (GND) | Ground Reference | Signal and power return path for all internal logic and output stages |
| 11–18 (B1–B8) | Port B Data I/O | Bi-directional TTL-compatible data terminals for second bus segment |
| 19 (OE) | Output Enable Input | Low enables outputs; High forces all outputs into high-impedance state |
| 20 (VCC) | Positive Supply | +5 V DC supply for logic core and output drivers |
Key Features
| Feature | Design Value |
|---|---|
| 3-State Outputs | Enables multi-drop bus sharing without contention; OE-controlled high-Z state isolates port during idle cycles |
| Dual-Bus Isolation | Independent A/B ports allow signal translation between physically separated subsystems with no internal coupling |
| TTL-Compatible Logic | Guaranteed VIL/VIH, IIL/IIH, and fan-out match standard 74LS family timing and loading behavior |
| DIR/OE Dual Control | Separate direction and enable signals provide deterministic bus arbitration timing - avoids metastability in synchronous systems |
| PDIP-20 Footprint | Mechanically and electrically interchangeable with SN74LS245, SN74LS640, and other 20-pin LS bus transceivers |
Applications
| Industrial PLC Backplanes | Legacy Test Equipment Interfaces |
|---|---|
Use Scenario: Bidirectional data exchange between CPU module and I/O expansion cards in DIN-rail mounted programmable logic controllers. IC Role / Device Role / Timing Role: Bus transceiver managing 8-bit parallel address/data multiplexing between isolated board stacks. Use Value: Enables hot-swap-safe bus isolation via OE control and eliminates need for discrete bus buffers or level shifters. | Use Scenario: Interfacing microcontroller-based test heads with legacy GPIB or parallel printer port peripherals. IC Role / Device Role / Timing Role: Level-translating bidirectional data bridge between 5 V TTL logic and older peripheral signaling standards. Use Value: Provides guaranteed 24 mA sink current per output to drive long traces and multiple TTL inputs without signal degradation. |
| Embedded Instrumentation Data Paths | Repair & Calibration Tooling |
Use Scenario: Routing sensor data and configuration commands between ADC/DAC modules and host controller in benchtop analyzers. IC Role / Device Role / Timing Role: Controlled-direction data conduit synchronized to system clock edges using DIR and OE timing windows. Use Value: Delivers ≤25 ns propagation delay with matched A→B and B→A paths, preserving timing integrity in sampled-data pipelines. | Use Scenario: Replacing obsolete transceivers in field-serviceable calibration equipment where footprint and pinout must match original design. IC Role / Device Role / Timing Role: Drop-in functional replacement for SN74LS245 or SN74LS640 in existing PDIP-20 sockets. Use Value: Maintains identical pin mapping, electrical specs, and thermal profile - no PCB rework or firmware changes required. |
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 8-bit non-inverting 3-state function; differs in DIR pin polarity (active-low vs. active-high on SN74LS645-1N) | Requires inverted DIR control signal; otherwise identical bus timing and drive strength | Select when existing design already uses SN74LS245 layout and only DIR logic inversion is needed |
| SN74LS640N | Identical pinout and electrical specs; differs only in internal logic - SN74LS640N is inverting, SN74LS645-1N is non-inverting | Swaps data polarity end-to-end; requires software or upstream logic compensation | Select when signal inversion is acceptable or already compensated in system architecture |
Compared with SN74LS245N and SN74LS640N, the SN74LS645-1N provides non-inverting data transfer with active-high direction control - simplifying timing alignment in synchronous bus designs where DIR is derived directly from address decode or state machine outputs without inversion logic.
Availability
SN74LS645-1N is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy test equipment interfaces, and embedded instrumentation data paths requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74LS645-1N 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 company founded in 1930, specializing in analog, embedded processing, and logic ICs with broad industrial and automotive qualification.
The SN74LS645-1N belongs to TI's legacy 74LS logic family, engineered for reliability in commercial-temperature industrial control, instrumentation, and repair applications where pin-compatible longevity matters.
FAQ
What is the maximum clock frequency supported by SN74LS645-1N in a synchronous bus application?
The SN74LS645-1N does not contain internal clock circuitry and is not a clocked device. However, its propagation delay (≤25 ns) and setup/hold timing allow reliable use in synchronous systems operating up to approximately 15 MHz, assuming proper PCB layout, termination, and load capacitance ≤15 pF per output. System-level timing must be verified with actual trace lengths and fan-out.
Does SN74LS645-1N support hot-swap or live-insertion on a powered bus?
No - the SN74LS645-1N lacks built-in hot-swap protection circuitry. While its 3-state outputs can isolate the device when OE is high, applying signal voltages before VCC is stable may cause latch-up or damage. For live-insertion, external protection (e.g., series resistors, TVS diodes, and power sequencing) is required. Always power VCC before applying data signals.
Can SN74LS645-1N be used as a direct replacement for SN74LS245 in an existing design?
SN74LS645-1N shares the same PDIP-20 package and pinout as SN74LS245, but DIR pin logic is inverted: SN74LS645-1N uses active-high DIR, while SN74LS245 uses active-low DIR. To substitute, invert the DIR control signal in firmware or hardware. All other electrical and timing parameters are functionally equivalent, making SN74LS645-1N a viable drop-in replacement with minor logic adjustment.
What is the recommended decoupling for SN74LS645-1N in a high-noise industrial environment?
TI recommends a minimum of one 0.1 µF ceramic capacitor placed as close as possible to pins 20 (VCC) and 10 (GND), with additional bulk capacitance (e.g., 10 µF tantalum) near the power entry point. In noisy environments, add ferrite beads in series with VCC and ground-plane stitching vias adjacent to the SN74LS645-1N footprint to suppress high-frequency coupling. Avoid shared return paths with switching loads.
Is SN74LS645-1N RoHS compliant and lead-free?
Yes - SN74LS645-1N is RoHS compliant and uses NiPdAu (NIPDAU) lead finish. Per TI's packaging addendum, it carries "Yes" in the RoHS column and meets JEDEC J-STD-020 moisture sensitivity Level-1 requirements. The part marking "SN74LS645-1N" appears on the top surface, and full compliance documentation is available in TI's official product change notices.
SN74LS645-1N Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- 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, 48mA
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 20-PDIP
SN74LS645-1N FAQ
1.How can I place an order for SN74LS645-1N through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS645-1N 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 SN74LS645-1N reliable?
The price and inventory of SN74LS645-1N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS645-1N is usually 5 days.
3.What payment methods are accepted for SN74LS645-1N?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS645-1N transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS645-1N?
SN74LS645-1N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS645-1N 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 SN74LS645-1N?
For technical support, including SN74LS645-1N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS645-1N requirements.
6.How does Aetrix verify that SN74LS645-1N is sourced from the original manufacturer or authorized distributors?
All SN74LS645-1N 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 SN74LS645-1N meets industry standards.
7.What is the process for return or replacement of SN74LS645-1N?
All SN74LS645-1N units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS645-1N, 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 SN74LS645-1N part is unused and in its original packaging.
Return procedure for SN74LS645-1N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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