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Texas Instruments SN74LS640-1NSR
- Part No.:
- SN74LS640-1NSR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.209", 5.30mm Width)
- Datasheet:
-
SN74LS640-1NSR.pdf
- Description:
- IC TRANSCEIVER INVERT 5.25V 20SO
- Quantity:
- Payment:
- Shipping:
Inventory:1,471
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Product details
Overview
SN74LS640-1NSR 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 with 5 V supply. It is used in legacy industrial backplane interfaces and microprocessor system expansion buses.
For engineers reviewing the SN74LS640-1NSR datasheet, SN74LS640-1NSR pinout, SN74LS640-1NSR application, or SN74LS640-1NSR equivalent, key selection criteria include its 3-state output drive capability, DIR/OE logic polarity, propagation delay under load, DC output current ratings, and SOP-20 package compatibility with through-hole and surface-mount board designs.
Technical Context
The SN74LS640-1NSR implements dual-function TTL-compatible bus interface logic: DIR pin determines data flow direction (A→B or B→A), while active-low OE enables/disables all outputs simultaneously. Its internal architecture uses standard LS-TTL bipolar circuitry with Schottky-clamped inputs and outputs, ensuring noise immunity and predictable switching thresholds at 5 V.
It supports hot-insertion-capable bus sharing via high-impedance 3-state outputs when OE is high, and guarantees compatible voltage levels with other 74LS-family devices-VOH ≥ 2.7 V (IO = –15 mA), VOL ≤ 0.5 V (IO = 20 mA)-enabling direct interconnection without level-shifting.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74LS (Low-power Schottky TTL), fully compatible with 74L, 74, and 74S families |
| Data Width | 8-bit bidirectional bus transceiver with non-inverting transfer |
| Supply Voltage | VCC = 4.75 V to 5.25 V - ensures stable operation across standard TTL rail tolerances |
| Propagation Delay | tPD = 20 ns max (A-to-B or B-to-A, CL = 15 pF) - defines maximum clock-to-data timing budget in synchronous bus designs |
| Output Drive | IOH = –15 mA / IOL = 20 mA - supports fan-out of up to 20 LS-TTL loads per output |
| Operating Temperature | 0°C to +70°C - qualified for commercial-grade embedded and instrumentation applications |
| Package | SOP (NS) with 20 pins, 1.27 mm pitch, RoHS-compliant NiPdAu lead finish |
Pinout & Package
SOP-20 (NS) package: 12.8 mm × 7.5 mm body, 2.65 mm max height, gull-wing leads, pin 1 marked by notch or bevel. Compatible with standard SOIC footprints and reflow profiles (MSL Level-1).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | High = A→B data flow; Low = B→A - determines signal path polarity for all 8 bits |
| 2–9 (A1–A8) | Port A Data I/O | Input when DIR=Low & OE=Low; output when DIR=High & OE=Low - connects to local bus or peripheral side |
| 10 (GND) | Ground Reference | Common return for all internal logic and output drivers - must be low-inductance connection |
| 11–18 (B1–B8) | Port B Data I/O | Input when DIR=High & OE=Low; output when DIR=Low & OE=Low - connects to system bus or controller side |
| 19 (OE) | Output Enable Input | Active-low: OE=Low enables outputs; OE=High forces all outputs to high-impedance state |
| 20 (VCC) | Power Supply | +5 V supply for all internal logic and output stages - requires local 0.1 µF ceramic decoupling |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional 3-state bus interface | Enables shared bus arbitration without external tri-state logic or bus buffers |
| Independent DIR and OE controls | Allows simultaneous direction setting and output gating - critical for burst-mode DMA transfers |
| LS-TTL input/output compatibility | Guarantees interoperability with legacy 74LS/74L/74-series logic without level translation |
| High noise immunity | VNIH = 2.0 V min, VNIL = 0.8 V max - rejects common-mode noise on industrial backplanes |
| SOP-20 RoHS-compliant packaging | Supports automated SMT assembly and meets modern environmental compliance requirements |
Applications
| Microprocessor System Expansion | Industrial Backplane Interface |
|---|---|
Use Scenario: Adding peripheral modules (e.g., ADC cards, relay controllers) to an 8085/8086-based industrial controller via parallel bus. IC Role / Device Role / Timing Role: Bidirectional data bridge between CPU local bus and expansion slot bus, synchronized to system clock edges. Use Value: Enables plug-and-play module addressing using DIR/OE handshaking, eliminating need for discrete bus switches or CPLDs. | Use Scenario: Interfacing multiple PLC I/O racks over a shared 8-bit parallel backplane with daisy-chained enable signals. IC Role / Device Role / Timing Role: Isolates rack-specific data lanes while allowing centralized direction control and selective output enable per rack. Use Value: Reduces backplane wiring complexity and supports hot-swap-safe 3-state isolation during rack insertion/removal. |
| Legacy Test Equipment Bus | Embedded Instrumentation Data Link |
Use Scenario: Connecting GPIB-to-parallel bridge logic inside aging benchtop DMMs or oscilloscopes requiring TTL-level bus extension. IC Role / Device Role / Timing Role: Translates and buffers GPIB-handshake-controlled data bursts onto internal 8-bit diagnostic bus. Use Value: Maintains signal integrity over 15 cm traces at 1 MHz burst rates, meeting IEEE 488.1 timing margins. | Use Scenario: Linking sensor front-end ASICs to main MCU in ruggedized environmental monitoring units deployed in remote field sites. IC Role / Device Role / Timing Role: Provides galvanically isolated (via external optocouplers) bidirectional data coupling between analog subsystem and digital core. Use Value: Delivers deterministic 20 ns propagation delay and ±15 mA drive - sufficient for 2 m ribbon cable runs at 500 kHz sustained throughput. |
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 transceiver, but with single-direction control (DIR only); no separate OE - outputs always enabled when DIR set | Lacks independent output disable; unsuitable where bus arbitration requires dynamic high-Z assertion | Select SN74LS245N only if direction control suffices and continuous drive is acceptable |
| SN74LS641NSR | Octal transceiver with open-collector outputs instead of 3-state - requires external pull-up resistors and cannot drive low-impedance buses directly | Used in wired-AND bus topologies (e.g., interrupt lines), not general-purpose data buses | Choose SN74LS641NSR only for shared-line signaling where passive pull-ups define logic high |
Compared with SN74LS245N and SN74LS641NSR, the SN74LS640-1NSR uniquely provides independent DIR and active-low OE control in a 3-state architecture - essential for time-multiplexed bus sharing, DMA coherency, and hot-plug-safe system expansion where output disable must be decoupled from direction setting.
Availability
SN74LS640-1NSR is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy microprocessor expansion systems, and embedded instrumentation data links requiring stable component supply and long-term obsolescence management.
Supply support for SN74LS640-1NSR 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 design.
The SN74LS640-1NSR belongs to TI's legacy 74LS logic product line, engineered for reliability and interoperability in industrial control, test equipment, and military-grade systems requiring proven, long-lifecycle components.
FAQ
What is the function of the DIR pin on the SN74LS640-1NSR?
The DIR (Direction) pin on the SN74LS640-1NSR controls data flow direction: when DIR is high, data passes from Port A to Port B; when DIR is low, data flows from Port B to Port A. This bidirectional capability allows the SN74LS640-1NSR to serve as a flexible bus coupler in systems requiring reversible data paths without external routing logic.
Does the SN74LS640-1NSR support hot-swapping in live backplane systems?
Yes - the SN74LS640-1NSR supports hot-swapping when the OE (Output Enable) pin is held high during insertion, forcing all outputs into high-impedance state. This prevents bus contention and signal corruption. The SN74LS640-1NSR's guaranteed 3-state leakage (IOZ ≤ ±10 µA) ensures safe insertion into powered systems, provided OE is asserted before power stabilization.
What is the maximum capacitive load the SN74LS640-1NSR can drive while maintaining specified timing?
The SN74LS640-1NSR is characterized for CL = 15 pF, with tPD ≤ 20 ns and tPLH/tPHL ≤ 25 ns. Driving loads >15 pF increases propagation delay nonlinearly and may cause overshoot; for 50 pF loads, delay exceeds 35 ns and output rise/fall times degrade beyond specification. Use the SN74LS640-1NSR only with PCB traces and stubs totaling ≤15 pF unless buffered.
Can the SN74LS640-1NSR be used with 3.3 V logic systems?
No - the SN74LS640-1NSR is strictly a 5 V TTL device. Its input thresholds (VIH = 2.0 V min, VIL = 0.8 V max) and output swing (VOH ≥ 2.7 V at –15 mA) are incompatible with 3.3 V CMOS logic levels. Interfacing with 3.3 V systems requires level-shifting circuitry; the SN74LS640-1NSR itself must be powered at 5 V and operated within its specified 4.75–5.25 V range.
Is there a drop-in replacement for the SN74LS640-1NSR with extended temperature range?
Yes - the SN54LS640J (CDIP-20, –55°C to +125°C) is the military-qualified counterpart with identical logic function, pinout, and timing. It shares the same DIR/OE control scheme and electrical characteristics, differing only in temperature rating and Pb-free exemption status. The SN54LS640J is not RoHS-compliant (uses SnPb finish) but offers full functional equivalence for harsh-environment applications.
SN74LS640-1NSR 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, 48mA
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SO
SN74LS640-1NSR FAQ
1.How can I place an order for SN74LS640-1NSR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS640-1NSR 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 SN74LS640-1NSR reliable?
The price and inventory of SN74LS640-1NSR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS640-1NSR is usually 5 days.
3.What payment methods are accepted for SN74LS640-1NSR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS640-1NSR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS640-1NSR?
SN74LS640-1NSR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS640-1NSR 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 SN74LS640-1NSR?
For technical support, including SN74LS640-1NSR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS640-1NSR requirements.
6.How does Aetrix verify that SN74LS640-1NSR is sourced from the original manufacturer or authorized distributors?
All SN74LS640-1NSR 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 SN74LS640-1NSR meets industry standards.
7.What is the process for return or replacement of SN74LS640-1NSR?
All SN74LS640-1NSR units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS640-1NSR, 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 SN74LS640-1NSR part is unused and in its original packaging.
Return procedure for SN74LS640-1NSR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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