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Texas Instruments SN74LS640N
- Part No.:
- SN74LS640N
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74LS640N.pdf
- Description:
- IC TXRX INVERT 5.25V 20DIP
- Quantity:
- Payment:
- Shipping:
Inventory:283
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Product details
Overview
SN74LS640N 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 across 0°C to 70°C with 5 V supply. It is commonly used in microprocessor bus interfacing and memory address/data multiplexing.
For engineers reviewing the SN74LS640N datasheet, SN74LS640N pinout, SN74LS640N application, or SN74LS640N equivalent, key selection considerations include its 3-state output capability, DIR/OE dual-control logic, TTL-compatible input thresholds, and PDIP-20 package compatibility with legacy through-hole PCB layouts.
Technical Context
The SN74LS640N implements two independent 4-bit bidirectional transceivers within a single 20-pin PDIP package, each with dedicated DIR and OE inputs. Its output drivers support high-impedance state when OE is high, and data direction is determined solely by the DIR signal level - low for A-to-B, high for B-to-A.
It uses standard LS-TTL circuitry with Schottky-clamped bipolar transistors, delivering typical propagation delay of 15 ns (max 25 ns), fan-out of 20 LS-TTL loads, and guaranteed noise margin of 0.4 V at VCC = 5 V. Input clamp diodes provide ESD protection per MIL-STD-883 Class 3B.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | LS-TTL - ensures compatibility with legacy 74LS-series systems and predictable timing margins |
| Function | Octal 3-state bidirectional bus transceiver - enables shared bus arbitration between two 8-bit subsystems |
| Supply Voltage | 4.75 V to 5.25 V - supports stable operation under standard TTL rail tolerances |
| Propagation Delay | 25 ns max (A→B or B→A) - defines worst-case timing budget for synchronous bus cycles |
| Output Drive | -15 mA sink / 5 mA source - sufficient to drive 20 LS-TTL inputs without external buffering |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded and industrial control applications |
| Package | PDIP-20 - through-hole mounting compatible with manual assembly and legacy test fixtures |
Pinout & Package
SN74LS640N is housed in a 20-pin plastic dual in-line package (PDIP) with 0.3-inch body width and standard 0.1-inch pin pitch. Pin 1 is located at the top-left corner adjacent to the notch or dot marking.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR1) | Direction control for lower 4-bit channel | Low = A→B data flow; High = B→A - enables independent channel direction setting |
| 2–5 (A1–A4) | Input/output port A (lower nibble) | Bidirectional I/O pins tied to local subsystem bus; high-impedance when OE1 = high |
| 6 (GND) | Ground reference | Primary return path for all internal logic and output drivers |
| 7–10 (B1–B4) | Input/output port B (lower nibble) | Bidirectional I/O pins tied to remote subsystem bus; driven only when OE1 = low and DIR1 set |
| 11 (OE1) | Output enable for lower 4-bit channel | High = all A1–A4/B1–B4 outputs in high-Z; Low = channel active per DIR1 state |
| 12–13, 15–16 (A5–A8, B5–B8) | Upper 4-bit bidirectional ports | Second independent transceiver channel with identical DIR2 (pin 14) and OE2 (pin 17) controls |
| 14 (DIR2) | Direction control for upper 4-bit channel | Functionally identical to DIR1 but isolated - allows mixed-direction 8-bit transfers |
| 17 (OE2) | Output enable for upper 4-bit channel | Independent enable allows partial bus gating (e.g., disable upper nibble while lower remains active) |
| 20 (VCC) | Positive supply | 5 V nominal power rail; decoupling capacitor required within 1 cm of pin for noise suppression |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent 4-bit channels | Enables simultaneous or asymmetric bidirectional data transfers - e.g., A→B on lower nibble while B→A on upper nibble |
| Separate DIR and OE controls per channel | Allows precise timing orchestration: OE can gate outputs without affecting DIR state, preventing bus contention during mode transitions |
| 3-state outputs with TTL-compatible levels | Output leakage < 20 µA in high-Z ensures no unintended loading of shared bus lines during inactive periods |
| LS-TTL propagation delay ≤25 ns | Supports 20 MHz bus clocking in synchronous designs with adequate setup/hold margin |
| PDIP-20 RoHS-compliant packaging | NiPdAu lead finish meets JEDEC J-STD-020 moisture sensitivity Level-1, enabling standard reflow or hand-soldering |
Applications
| Microprocessor System Bus Interface | Memory Address/Data Multiplexing |
|---|---|
Use Scenario: Interfacing an 8-bit microprocessor (e.g., Z80 or 8085) to peripheral devices sharing a common data bus. IC Role / Device Role / Timing Role: SN74LS640N acts as a bidirectional data buffer, isolating CPU data lines from peripherals and enabling read/write direction control via DIR and OE signals. Use Value: Eliminates need for separate input and output latches; reduces component count and PCB area versus discrete latch + driver solutions. | Use Scenario: Demultiplexing time-shared address/data bus in early microcomputer designs using 8282/8283 latches. IC Role / Device Role / Timing Role: SN74LS640N provides controlled bidirectional transfer between AD0–AD7 and internal CPU registers or external RAM chips. Use Value: Supports clean bus turnaround with minimal dead time - DIR change synchronized to clock edge avoids metastability in shared-bus arbitration. |
| Industrial Control Backplane | Legacy Test Equipment Data Routing |
Use Scenario: Connecting modular I/O cards to a central controller over a parallel backplane in programmable logic controllers (PLCs). IC Role / Device Role / Timing Role: SN74LS640N serves as a hot-swappable bus isolator, allowing card insertion/removal without disrupting active communication on other slots. Use Value: High-impedance outputs prevent backplane signal corruption during card initialization or fault conditions. | Use Scenario: Reconfigurable signal routing in automated test equipment (ATE) where DUT interface requirements vary across product families. IC Role / Device Role / Timing Role: SN74LS640N functions as a manually or firmware-controlled bus switch, directing stimulus/response data between test vectors and DUT pins. Use Value: Pin-compatible replacement for obsolete 74LS245 in repair and upgrade scenarios - preserves existing PCB layout and firmware logic. |
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 8-bit channel with shared DIR/OE; no dual-channel independence | Lacks per-nibble control - unsuitable for mixed-direction 8-bit transfers | Select when full 8-bit unidirectional or simple bidirectional buffering suffices and board space is constrained |
| SN74ALS640N | Advanced LS variant: 2× faster propagation (12 ns typ), lower power (19 mW vs 48 mW), same pinout | Higher speed enables tighter timing margins but requires stricter VCC regulation and layout | Prefer for new designs needing improved performance without changing PCB layout or firmware logic |
Compared with SN74LS245N, SN74LS640N offers finer-grained bus control via dual independent channels; compared with SN74ALS640N, it trades speed and power efficiency for broader voltage tolerance and proven field reliability in temperature-stable environments.
Availability
SN74LS640N is available at Aetrix Electronics and suitable for microprocessor bus interfacing, industrial control backplanes, and legacy test equipment requiring stable component supply and long-term obsolescence management.
Supply support for SN74LS640N 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 ICs with deep heritage in TTL and CMOS technologies.
The SN74LS640N belongs to TI's classic 74LS logic family, engineered for robustness and interoperability in industrial, computing, and instrumentation systems where reliability and long-term availability are critical.
FAQ
What is the maximum clock frequency supported by SN74LS640N in a synchronous bus application?
The SN74LS640N does not contain internal clock circuitry and is not rated for clock frequency. Its usable data rate depends on system-level timing: with 25 ns max propagation delay and typical setup/hold requirements, it supports reliable operation up to approximately 20 MHz in well-designed TTL buses. Actual frequency must be validated against the full timing budget of the specific SN74LS640N implementation, including trace length, loading, and driver strength.
Can SN74LS640N be used as a direct replacement for SN74LS245N on an existing PCB?
No - SN74LS640N is not a pin-compatible replacement for SN74LS245N. While both are 20-pin PDIP octal transceivers, their pin assignments differ significantly: SN74LS640N dedicates pins to dual DIR/OE controls and split 4-bit ports, whereas SN74LS245N uses a single DIR/OE pair and unified 8-bit I/O banks. Direct substitution would cause functional failure or bus contention without PCB revision.
Does SN74LS640N support hot-swap or live-insertion in backplane applications?
SN74LS640N has no built-in hot-swap protection, but its 3-state outputs and input clamp diodes allow safe use in hot-swap contexts when combined with external current-limiting resistors and power sequencing. During insertion, OE should be held high until VCC stabilizes and control signals settle; TI's application note SNLA133 documents recommended practices for implementing SN74LS640N in such systems.
What is the recommended decoupling strategy for SN74LS640N in high-noise industrial environments?
Place a 0.1 µF ceramic capacitor between VCC (pin 20) and GND (pin 6) within 5 mm of the SN74LS640N package, plus a 4.7 µF tantalum or aluminum electrolytic capacitor near the board's main 5 V rail. For multi-SN74LS640N systems, use individual 0.1 µF caps per device and share the bulk capacitor. Avoid daisy-chaining ground connections - route each SN74LS640N's GND directly to a solid ground plane.
Is SN74LS640N compliant with modern RoHS directives?
Yes - the SN74LS640N variant supplied by Aetrix Electronics carries NiPdAu (nickel-palladium-gold) lead finish and is RoHS-compliant per Directive 2011/65/EU. The "N" suffix denotes PDIP packaging with lead-free terminations; TI's packaging addendum confirms RoHS status and MSL Level-1 rating for this orderable part number.
SN74LS640N 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, 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
SN74LS640N FAQ
1.How can I place an order for SN74LS640N through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS640N 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 SN74LS640N reliable?
The price and inventory of SN74LS640N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS640N is usually 5 days.
3.What payment methods are accepted for SN74LS640N?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS640N transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS640N?
SN74LS640N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS640N 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 SN74LS640N?
For technical support, including SN74LS640N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS640N requirements.
6.How does Aetrix verify that SN74LS640N is sourced from the original manufacturer or authorized distributors?
All SN74LS640N 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 SN74LS640N meets industry standards.
7.What is the process for return or replacement of SN74LS640N?
All SN74LS640N units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS640N, 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 SN74LS640N part is unused and in its original packaging.
Return procedure for SN74LS640N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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