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Texas Instruments SN74LS640DWR
- Part No.:
- SN74LS640DWR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74LS640DWR.pdf
- Description:
- IC TXRX INVERT 5.25V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,364
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Product details
Overview
SN74LS640DWR 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 typical propagation delay of 15 ns at VCC = 5 V.
For engineers reviewing the SN74LS640DWR datasheet, SN74LS640DWR pinout, SN74LS640DWR application, or SN74LS640DWR equivalent, this device serves as a legacy-compatible bus interface solution for industrial control backplanes, legacy instrumentation data buses, and retro-computing system upgrades requiring TTL-compatible 3-state drive capability.
Technical Context
The SN74LS640DWR implements dual 4-bit or single 8-bit bidirectional data transfer using separate DIR and OE inputs. Its internal architecture consists of eight identical transceiver cells, each with symmetrical input/output impedance and guaranteed TTL-compatible voltage thresholds (VIH = 2.0 V min, VIL = 0.8 V max).
It supports hot-insertion tolerant operation only when powered and biased per TI's LS-family guidelines; no built-in ESD protection beyond standard 2 kV HBM. Output drive strength is rated at IOH = –15 mA and IOL = 24 mA under nominal conditions, enabling direct connection to standard TTL loads without external pull-ups.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74LS (Low-power Schottky TTL), fully compatible with 74L, 74S, and 74F logic interfaces |
| Data Width | 8-bit bidirectional bus transceiver with non-inverting data path |
| Propagation Delay | 15 ns typical (A→B or B→A), critical for synchronous bus timing budgets up to 33 MHz |
| Output Drive | IOL = 24 mA / IOH = –15 mA, sufficient to drive 10 standard TTL loads per output |
| Supply Voltage | VCC = 4.75 V to 5.25 V, strict 5 V operation-no wide-VCC support |
| Operating Temperature | 0°C to +70°C, commercial-grade rating suitable for enclosed industrial enclosures |
| 3-State Enable Time | tpd(OE→Y) = 15 ns max, enabling precise bus arbitration timing |
Pinout & Package
SN74LS640DWR is housed in a 20-pin SOIC (DW) package measuring 7.5 mm × 12.8 mm × 2.65 mm, with 1.27 mm pitch, RoHS-compliant NiPdAu lead finish, and moisture sensitivity level (MSL) 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; determines signal path polarity |
| 2–9 (A1–A8) | Port A Data I/O | Bi-directional TTL-compatible bus port; driven high/low or tri-stated based on DIR/OE |
| 10 (GND) | Ground Reference | Signal and power return for all internal logic and output stages |
| 11–18 (B1–B8) | Port B Data I/O | Bi-directional TTL-compatible bus port; complementary to A-side with DIR-controlled direction |
| 19 (OE) | Output Enable Input | Active-low; when high, all outputs enter high-impedance state regardless of DIR |
| 20 (VCC) | Power Supply | +5 V DC supply; decoupling capacitor required within 10 mm of pin for noise immunity |
Key Features
| Feature | Design Value |
|---|---|
| Independent DIR and OE controls | Enables flexible bus arbitration: direction can be set while outputs remain disabled, preventing bus contention during state transitions |
| TTL-compatible input thresholds | VIL ≤ 0.8 V and VIH ≥ 2.0 V ensure reliable interfacing with legacy 74-series, microprocessor address/data buses, and discrete logic |
| Matched propagation delays | A→B and B→A delays differ by ≤2 ns, supporting deterministic timing in full-duplex or time-multiplexed bus architectures |
| High-impedance isolation | Outputs achieve >100 kΩ off-state resistance, eliminating leakage current paths between isolated bus segments |
| SOIC packaging with MSL-1 rating | Supports standard reflow assembly without dry-pack requirements, reducing manufacturing overhead for legacy-replacement builds |
Applications
| Industrial Backplane Interface | Retrocomputing Bus Expansion |
|---|---|
Use Scenario: Interfacing a modern microcontroller module to a legacy 8-bit ISA-style backplane carrying address, data, and control signals. IC Role / Device Role / Timing Role: Bidirectional level-shifting and bus-driving transceiver that isolates controller I/O from noisy backplane transients while maintaining TTL timing integrity. Use Value: Eliminates need for discrete buffer arrays; enables drop-in replacement of failed SN74LS245 units with identical pinout and timing behavior. | Use Scenario: Adding peripheral expansion capability to a 1980s-era Z80-based computer system using original-spec bus protocols. IC Role / Device Role / Timing Role: Synchronizing data transfers between CPU bus and add-on memory or I/O cards operating at native 4–6 MHz clock rates. Use Value: Matches vintage 74LS timing parameters exactly, avoiding race conditions or setup/hold violations observed with faster CMOS alternatives. |
| Test Equipment Data Acquisition | Programmable Logic Controller (PLC) I/O Module |
Use Scenario: Routing sensor data from multiple analog-to-digital converter channels into a centralized FPGA-based acquisition engine via shared parallel bus. IC Role / Device Role / Timing Role: Controlled bus gate managing time-sliced access to ADC result registers, coordinated via FPGA-generated DIR/OE strobes. Use Value: Provides predictable 15 ns latency and 24 mA drive-sufficient to overcome trace capacitance across 15 cm PCB runs without signal degradation. | Use Scenario: Isolating field I/O bus from internal PLC processor bus in DIN-rail mounted controllers subject to EMI and ground potential shifts. IC Role / Device Role / Timing Role: Electrically isolating but logically transparent data conduit between isolated power domains, with OE used for fault-safe bus shutdown. Use Value: Enables fail-safe bus disable via OE assertion during watchdog timeout or overtemperature events, preventing spurious I/O writes. |
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 function, but uses single active-low OE (no DIR pin); direction fixed by external wiring | Suitable only where bus direction is static or controlled externally (e.g., dedicated address vs. data lines) | Select when board layout already routes fixed-direction paths and DIR logic is unnecessary |
| SN74ALS640DWR | Advanced Low-Power Schottky version: 2× lower power (19 mW vs. 45 mW), 30% faster (10 ns delay), same pinout and voltage specs | Better suited for thermally constrained or higher-speed legacy upgrades where power budget or timing margin is tight | Prefer for new designs needing improved efficiency or margin; pin-compatible with SN74LS640DWR |
Compared with SN74LS245N, SN74LS640DWR offers dynamic direction control without external logic; compared with SN74ALS640DWR, it trades speed and power for broader legacy compatibility and established thermal behavior in long-deployed systems.
Availability
SN74LS640DWR is available at Aetrix Electronics and suitable for industrial backplane interfaces, retrocomputing bus expansions, and test equipment data acquisition systems requiring stable component supply and long-term obsolescence management.
Supply support for SN74LS640DWR 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic ICs with leadership in industrial, automotive, and aerospace markets.
The SN74LS640DWR belongs to TI's legacy 74LS logic family, engineered for robustness and interoperability in mission-critical industrial control and instrumentation systems deployed since the 1980s.
FAQ
What is the maximum clock frequency supported by SN74LS640DWR?
The SN74LS640DWR is not a clocked device-it has no internal clock and operates asynchronously. Its usable data rate depends on system-level timing margins. With a typical propagation delay of 15 ns and setup/hold times under 5 ns, it supports reliable bus handshaking up to approximately 33 MHz in well-terminated, low-capacitance layouts. Actual maximum frequency must be validated per PCB trace length, loading, and controller timing constraints in the target SN74LS640DWR application.
Can SN74LS640DWR be used with 3.3 V logic systems?
No, SN74LS640DWR is strictly a 5 V TTL device and is not 3.3 V tolerant. Its input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V) and output voltages (VOH ≈ 3.4 V min, VOL ≈ 0.35 V max at IOL = 24 mA) are specified only for VCC = 4.75–5.25 V. Direct connection to 3.3 V logic may cause unreliable switching or excessive input current. Level translation is required for interoperability with SN74LS640DWR in mixed-voltage systems.
Does SN74LS640DWR support hot-swap insertion?
SN74LS640DWR does not include hot-swap protection circuitry. While its 3-state outputs can be asserted before power-up to minimize bus disturbance, TI documentation requires VCC to be stable and within specification before applying input signals. Uncontrolled hot insertion risks latch-up or parametric shift due to unpowered I/O pins receiving voltage. For true hot-swap capability, external protection (e.g., series resistors, dedicated hot-swap controllers) must be added in the SN74LS640DWR design.
What is the difference between SN74LS640DWR and SN74LS640N?
SN74LS640DWR and SN74LS640N share identical logic functionality, electrical specifications, and pinout-but differ in packaging and packaging-related attributes. SN74LS640DWR uses a 20-pin SOIC (DW) package supplied in tape-and-reel (2000 pcs), with MSL-1 rating and NiPdAu lead finish. SN74LS640N uses a 20-pin PDIP (N) package supplied in tubes (20 pcs), with no MSL rating and NIPDAU finish. Both operate from 0°C to 70°C and are RoHS-compliant.
Is SN74LS640DWR still in active production?
Yes, SN74LS640DWR is marked "Active" in TI's official packaging addendum (as of July 2026). It remains in ongoing production with standard lead times, full datasheet support, and no announced discontinuance. TI continues to manufacture and distribute SN74LS640DWR for legacy system maintenance, repair, and industrial replacement demand.
SN74LS640DWR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-SOIC (0.295", 7.50mm 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-SOIC
SN74LS640DWR FAQ
1.How can I place an order for SN74LS640DWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS640DWR 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 SN74LS640DWR reliable?
The price and inventory of SN74LS640DWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS640DWR is usually 5 days.
3.What payment methods are accepted for SN74LS640DWR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS640DWR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS640DWR?
SN74LS640DWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS640DWR 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 SN74LS640DWR?
For technical support, including SN74LS640DWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS640DWR requirements.
6.How does Aetrix verify that SN74LS640DWR is sourced from the original manufacturer or authorized distributors?
All SN74LS640DWR 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 SN74LS640DWR meets industry standards.
7.What is the process for return or replacement of SN74LS640DWR?
All SN74LS640DWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS640DWR, 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 SN74LS640DWR part is unused and in its original packaging.
Return procedure for SN74LS640DWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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