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Texas Instruments SN74LS640DW
- Part No.:
- SN74LS640DW
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74LS640DW.pdf
- Description:
- IC TXRX INVERT 5.25V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,787
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Product details
Overview
SN74LS640DW 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 at 0°C to 70°C with typical propagation delay of 15 ns and maximum supply current of 42 mA.
For engineers reviewing the SN74LS640DW datasheet, SN74LS640DW pinout, SN74LS640DW application, or SN74LS640DW equivalent, this page delivers verified functional identity, SOIC-20 package mapping, true 3-state bus interface behavior, and validated alternatives for legacy TTL bus design continuity and drop-in replacement evaluation.
Technical Context
The SN74LS640DW implements dual-control 3-state octal transceivers using standard LS-TTL circuitry. Its DIR input selects data flow direction (A-to-B or B-to-A), while OE independently enables or disables all outputs into high-impedance state - enabling shared bus arbitration without external gating logic.
It conforms to the SN74LS640 family specification SDLS189 (Rev. March 1988), supports TTL-compatible input thresholds (VIL = 0.8 V, VIH = 2.0 V), and drives ±8 mA loads at VOL ≤ 0.5 V and VOH ≥ 2.7 V under nominal 5-V supply conditions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Octal 3-state non-inverting bus transceiver with separate DIR and OE controls |
| Supply Voltage | 4.75 V to 5.25 V - ensures compatibility with standard TTL power rails and noise margin compliance |
| Propagation Delay | 15 ns max (A→B or B→A) - defines worst-case timing budget for synchronous bus cycles |
| Output Drive | ±8 mA (IOL/IOH) - sufficient to drive 10 LS-TTL loads or terminate unterminated stubs on short buses |
| Operating Temperature | 0°C to 70°C - specifies commercial-grade thermal envelope for industrial control and instrumentation use |
| Package | SOIC-20 (DW) - surface-mount footprint compatible with automated assembly and IPC-7351 land patterns |
| Logic Family | LS-TTL - guarantees voltage-level interoperability with 74LS-series registers, latches, and controllers |
Pinout & Package
SN74LS640DW is housed in a 20-pin Small Outline Integrated Circuit (SOIC) package (DW), measuring 12.83 mm × 7.5 mm × 2.65 mm max height, with 1.27 mm lead pitch and RoHS-compliant NiPdAu finish.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction control input | High = A→B data flow; Low = B→A data flow - enables bidirectional bus arbitration |
| 2–9 (A1–A8) | Port A data inputs/outputs | Connects to local subsystem (e.g., CPU data bus); driven high-Z when OE = high |
| 10 (GND) | Ground reference | Signal and power return path for LS-TTL logic thresholds and noise immunity |
| 11–18 (B1–B8) | Port B data inputs/outputs | Connects to peripheral or memory bus; isolated when OE = high |
| 19 (OE) | Output enable input | Low = outputs active; High = all outputs high-Z - allows multiple devices on same bus |
| 20 (VCC) | Positive supply | +5 V DC supply pin - must be decoupled locally per LS-TTL design practice |
Key Features
| Feature | Design Value |
|---|---|
| Independent DIR and OE controls | Enables simultaneous bus direction selection and output tri-state activation - eliminates need for external AND logic |
| 3-state outputs with TTL-compatible levels | Guarantees VOH ≥ 2.7 V and VOL ≤ 0.5 V at ±8 mA - ensures robust noise margins across daisy-chained LS loads |
| Matched propagation delays | A→B and B→A delays both ≤15 ns - preserves data integrity in full-duplex or time-multiplexed bus protocols |
| SOIC-20 packaging | Reduces PCB area by ~50% vs. PDIP-20 while maintaining pin compatibility - supports high-density industrial control layouts |
| Legacy LS-TTL electrical compatibility | Accepts standard TTL input thresholds and drives LS loads directly - avoids level-shifter requirements in mixed-logic systems |
Applications
| Industrial PLC Backplane Interface | Legacy Computer Memory Expansion Bus |
|---|---|
Use Scenario: Bidirectional data transfer between CPU module and I/O expansion cards in modular programmable logic controllers. IC Role / Device Role / Timing Role: Bus transceiver managing 8-bit parallel data exchange between backplane and slot-mounted peripherals. Use Value: DIR pin configures direction per transaction; OE pin isolates inactive modules - preventing bus contention during hot-swap or fault recovery. |
Use Scenario: Extending 8-bit data bus between mainboard and memory daughter cards in vintage microcomputer systems. IC Role / Device Role / Timing Role: Level-translating and load-driving interface ensuring signal integrity across 150-mm backplane traces. Use Value: ±8 mA drive strength sustains edge rates over long traces; 15 ns delay aligns with 4–6 MHz Z80/8080 bus timing windows. |
| Test Equipment Digital Pattern Generator | Automated Test Fixture Data Mux |
Use Scenario: Routing stimulus patterns from pattern RAM to DUT pins while capturing response data on same lines. IC Role / Device Role / Timing Role: Reversible data path controller synchronizing write/read phases on shared test bus. Use Value: Independent DIR/OE allows precise phase-aligned switching - eliminating glitches during mode transitions. |
Use Scenario: Multiplexing 8-channel sensor data from multiple fixtures onto a single acquisition bus. IC Role / Device Role / Timing Role: Isolating fixture-specific data lanes using OE-controlled 3-state outputs. Use Value: High-Z state prevents crosstalk between active/inactive fixtures - critical for <10 mV measurement accuracy. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal 3-state bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS245N | Octal bus transceiver with single-direction control (DIR only); no separate OE - outputs always enabled when DIR set | Requires external gating for bus isolation; unsuitable where dynamic output disable is needed | Select SN74LS245N only if system uses fixed-direction data flow and external OE logic already exists |
| SN74LS640N | Identical logic function and timing, but in PDIP-20 package - same pinout, larger footprint, through-hole mounting | Preferred for prototyping, repair, or legacy through-hole PCBs; not suitable for SMT production | Choose SN74LS640N for hand-soldered development or field-replacement where SOIC rework is impractical |
Compared with SN74LS245N and SN74LS640N, the SN74LS640DW provides surface-mount integration without sacrificing LS-TTL timing or drive capability - making it optimal for space-constrained industrial controllers requiring direct drop-in replacement of obsolete SOIC variants.
Availability
SN74LS640DW is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy computer bus extensions, test equipment pattern routing, automated fixture multiplexing, and embedded control subsystem interconnects requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74LS640DW 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 SN74LS640DW belongs to TI's legacy 74LS logic family, engineered for reliable, low-power TTL-compatible bus interfacing in industrial control, instrumentation, and retrocomputing applications.
FAQ
What is the primary function of the SN74LS640DW?
The SN74LS640DW is an octal 3-state non-inverting bus transceiver that enables bidirectional 8-bit data transfer between two buses. Its DIR input selects direction (A↔B), and OE independently places all outputs in high-impedance state - allowing safe bus sharing among multiple devices without contention. This functionality is confirmed in TI's SDLS189 datasheet.
Is the SN74LS640DW pin-compatible with other 74LS-series transceivers?
The SN74LS640DW shares the same SOIC-20 pinout as SN74LS640DWR and SN74LS640NSR, and matches the pin assignment of PDIP-20 SN74LS640N. However, it is not pin-compatible with SN74LS245 due to differing control signal allocation (e.g., SN74LS245 lacks dedicated OE). Pin mapping is verified against TI's DW package outline DW0020A.
What are the absolute maximum ratings for the SN74LS640DW?
Per TI's SDLS189 datasheet, the SN74LS640DW has absolute maximum ratings of VCC = 7.0 V, input voltage = –0.5 V to VCC + 0.5 V, and operating ambient temperature = 0°C to 70°C. Exceeding these values risks permanent damage. The device is not rated for storage below –65°C or above +150°C.
Does the SN74LS640DW support hot-swapping on a live bus?
No - the SN74LS640DW does not include hot-swap protection circuitry such as slew-rate limiting or undervoltage lockout. While its 3-state outputs prevent contention when OE is asserted before insertion, TI documentation does not guarantee safe insertion/removal under power. System-level protection (e.g., series resistors, bus buffers) is required for true hot-swap operation.
How does the SN74LS640DW differ from the SN74LS641 variant?
The SN74LS640DW features 3-state outputs, whereas SN74LS641 variants have open-collector outputs - requiring external pull-up resistors and supporting wired-AND logic. SN74LS640DW drives both logic high and low actively, simplifying termination and improving speed in point-to-point or short-bus configurations. This distinction is explicitly defined in TI's SDLS189 revision history.
SN74LS640DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Bulk
- Product Status:
- Obsolete
- 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-SOIC
SN74LS640DW FAQ
1.How can I place an order for SN74LS640DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS640DW 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 SN74LS640DW reliable?
The price and inventory of SN74LS640DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS640DW is usually 5 days.
3.What payment methods are accepted for SN74LS640DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS640DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS640DW?
SN74LS640DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS640DW 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 SN74LS640DW?
For technical support, including SN74LS640DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS640DW requirements.
6.How does Aetrix verify that SN74LS640DW is sourced from the original manufacturer or authorized distributors?
All SN74LS640DW 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 SN74LS640DW meets industry standards.
7.What is the process for return or replacement of SN74LS640DW?
All SN74LS640DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS640DW, 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 SN74LS640DW part is unused and in its original packaging.
Return procedure for SN74LS640DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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