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Texas Instruments SN74LS640NSR
- Part No.:
- SN74LS640NSR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.209", 5.30mm Width)
- Datasheet:
-
SN74LS640NSR.pdf
- Description:
- IC TRANSCEIVER INVERT 5.25V 20SO
- Quantity:
- Payment:
- Shipping:
Inventory:4,471
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Product details
Overview
SN74LS640NSR 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 at 0°C to 70°C with typical propagation delay of 15 ns and maximum supply current of 40 mA.
For engineers reviewing the SN74LS640NSR datasheet, SN74LS640NSR pinout, SN74LS640NSR application, or SN74LS640NSR equivalent, this device is selected for legacy industrial control backplanes, vintage microprocessor data bus interfacing, and TTL-compatible memory expansion where 3-state bus arbitration and deterministic timing are required.
Technical Context
The SN74LS640NSR implements dual-function control logic: DIR selects data flow direction (A→B or B→A), while OE independently enables or disables all eight outputs into high-impedance state. Its TTL-compatible input thresholds (VIL = 0.8 V, VIH = 2.0 V) and output drive capability (IOL = 24 mA, IOH = –0.4 mA) ensure interoperability with standard LS-TTL logic families.
It uses bipolar Schottky-clamped transistor technology, delivering guaranteed DC performance across its full operating temperature range and supporting synchronous bus handshaking without external latching. No internal pull-ups or level-shifting circuitry is present - all signals remain strictly TTL-voltage-referenced.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Octal non-inverting 3-state bus transceiver with separate DIR and OE controls |
| Supply Voltage (VCC) | 4.75 V to 5.25 V - ensures compatibility with regulated +5 V TTL power rails |
| Propagation Delay (tPD) | 15 ns max (A-to-B or B-to-A) - enables reliable operation up to ~30 MHz bus toggle rates |
| Output Drive (IOL/IOH) | 24 mA sink / –0.4 mA source - supports direct fan-out to 20 LS-TTL inputs |
| Input Thresholds | VIL ≤ 0.8 V, VIH ≥ 2.0 V - guarantees noise margin >400 mV in standard TTL environments |
| Operating Temperature | 0°C to +70°C - qualified for commercial-grade embedded and instrumentation applications |
| Package | SOP (NS) with 20 pins - surface-mount compatible, 1.27 mm pitch, RoHS-compliant NIPDAU finish |
Pinout & Package
SOP (NS) package: 20-pin small-outline plastic package, 7.5 mm body width, 2.65 mm max height, gull-wing leads, RoHS-compliant NIPDAU plating, MSL Level-1 (unlimited floor life at ≤30°C/60% RH).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction control input | High = A→B data flow; Low = B→A data flow - asynchronous, no setup/hold required |
| 2–9 (A1–A8) | Port A data inputs/outputs | Bidirectional I/O pins tied to local bus segment; high-impedance when OE = high |
| 10 (GND) | Ground reference | Signal and power return for all internal logic and output drivers |
| 11–18 (B1–B8) | Port B data inputs/outputs | Bidirectional I/O pins tied to remote bus segment; high-impedance when OE = high |
| 19 (OE) | Output enable input | Low = outputs active; High = all outputs in high-Z - overrides DIR state |
| 20 (VCC) | Positive supply | +5 V DC power connection; decoupling capacitor required within 10 mm |
Key Features
| Feature | Design Value |
|---|---|
| Independent DIR and OE controls | Enables flexible bus arbitration: direction and output state managed separately for precise timing control |
| 3-state outputs with TTL-compatible drive | Supports wired-OR bus topologies and eliminates contention during multi-master access |
| Matched A/B propagation delays | Ensures symmetrical timing behavior regardless of data flow direction - critical for synchronous bus protocols |
| Standard LS-TTL electrical interface | Direct drop-in replacement for legacy 74LS245 in existing designs without level-shifting or biasing changes |
| SOP (NS) packaging | Enables automated SMT assembly with industry-standard reflow profile (Level-1, 260°C peak) |
Applications
| Industrial Backplane Interface | Microprocessor Data Bus Extension |
|---|---|
Use Scenario: Isolating CPU address/data buses from peripheral expansion slots in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional data conduit enabling read/write cycles between MPU and add-on I/O modules. Use Value: Prevents bus contention during slot insertion/removal via OE-controlled high-Z state and supports deterministic 15 ns latency for real-time I/O response. |
Use Scenario: Extending Z80 or 8085 data bus width between main board and memory daughter cards. IC Role / Device Role / Timing Role: Directional buffer managing data flow during memory read (B→A) and write (A→B) operations. Use Value: Matches LS-TTL timing budgets and provides 24 mA sink capability to drive long traces and multiple loads without signal degradation. |
| Legacy Test Equipment Bus Arbitration | TTL-Based Instrumentation Subsystem Link |
Use Scenario: Sharing a common GPIB or IEEE-488-compatible control bus among multiple instrument modules. IC Role / Device Role / Timing Role: Controlled bus isolator allowing one module to drive while others tri-state. Use Value: Eliminates need for discrete bus switches; DIR/OE separation permits pre-arming direction before enabling outputs. |
Use Scenario: Interfacing ADC/DAC boards with host controller in benchtop signal generators and spectrum analyzers. IC Role / Device Role / Timing Role: Level-consistent data translator between subsystems using identical TTL voltage thresholds. Use Value: Maintains noise immunity with 400 mV input hysteresis margin and avoids timing skew between channels due to matched A/B path delays. |
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 OE control only (no DIR pin); requires external direction logic or fixed unidirectional use | Limited to fixed-direction or externally controlled bidirectional operation | Select when direction is static or managed by separate gates; lower pin count but less flexible control |
| SN74LS641NSR | Open-collector outputs instead of 3-state; requires external pull-up resistors on B-side | Suitable for wired-AND bus structures and interrupt line sharing, not general-purpose bidirectional data transfer | Choose for shared interrupt or status lines where active-low open-collector behavior is required |
Compared with SN74LS245N and SN74LS641NSR, the SN74LS640NSR uniquely integrates independent DIR and OE in a single 20-pin SOP package, enabling fully software-controllable bidirectional bus arbitration without external components - essential for dynamic bus mastership in legacy embedded systems.
Availability
SN74LS640NSR is available at Aetrix Electronics and suitable for industrial backplane interfaces, microprocessor data bus extensions, and legacy test equipment bus arbitration requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74LS640NSR 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, automotive, and communications reach.
The SN74LS640NSR belongs to TI's legacy 74LS logic family, engineered specifically for robust, low-cost, TTL-compatible digital interconnect in commercial-grade control and instrumentation systems.
FAQ
What is the primary function of the SN74LS640NSR?
The SN74LS640NSR is an octal non-inverting bus transceiver with independent direction (DIR) and output-enable (OE) controls. It allows bidirectional 8-bit data transfer between two TTL-compatible buses, placing all outputs in high-impedance state when OE is high - making it ideal for bus arbitration in legacy microprocessor and industrial control systems.
Does the SN74LS640NSR support hot-swap or live-insertion?
No, the SN74LS640NSR does not include hot-swap protection circuitry. Its TTL inputs lack ESD clamps rated for live insertion, and powering the device while bus lines are active may cause latch-up or damage. Always power-cycle the system before inserting or removing the SN74LS640NSR in socketed applications.
Can the SN74LS640NSR be used as a level shifter between 3.3 V and 5 V systems?
No, the SN74LS640NSR is strictly a 5 V TTL device with VCC = 4.75–5.25 V and input thresholds referenced to 5 V. It cannot safely accept 3.3 V logic levels (VIH minimum is 2.0 V, but DC noise margin collapses), nor does it provide 3.3 V-compatible outputs. Use dedicated level translators like TXB0108 for mixed-voltage interfacing.
What is the maximum clock or data toggle rate supported by the SN74LS640NSR?
The SN74LS640NSR has a maximum propagation delay of 15 ns, supporting reliable data toggling up to approximately 30 MHz under ideal loading conditions. Real-world bus speed depends on trace capacitance, fan-out, and termination; for sustained 20+ MHz operation, keep stub lengths under 5 cm and use point-to-point routing.
Is there a pin-compatible drop-in replacement for the SN74LS640NSR in modern packaging?
No RoHS-compliant, drop-in pin-compatible replacement exists for the SN74LS640NSR. TI discontinued newer-generation equivalents with identical pinout and logic behavior. The SN74LS640NSR remains the only actively produced version in SOP (NS) packaging; alternatives like SN74LS245 require PCB redesign due to differing pin assignments and control architecture.
SN74LS640NSR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-SOIC (0.209", 5.30mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Logic Type:
- Transceiver, 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:
- Surface Mount
- Supplier Device Package:
- 20-SO
SN74LS640NSR FAQ
1.How can I place an order for SN74LS640NSR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS640NSR 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 SN74LS640NSR reliable?
The price and inventory of SN74LS640NSR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS640NSR is usually 5 days.
3.What payment methods are accepted for SN74LS640NSR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS640NSR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS640NSR?
SN74LS640NSR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS640NSR 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 SN74LS640NSR?
For technical support, including SN74LS640NSR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS640NSR requirements.
6.How does Aetrix verify that SN74LS640NSR is sourced from the original manufacturer or authorized distributors?
All SN74LS640NSR 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 SN74LS640NSR meets industry standards.
7.What is the process for return or replacement of SN74LS640NSR?
All SN74LS640NSR units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS640NSR, 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 SN74LS640NSR part is unused and in its original packaging.
Return procedure for SN74LS640NSR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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