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Texas Instruments SN74AS640DW
- Part No.:
- SN74AS640DW
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74AS640DW.pdf
- Description:
- IC TXRX INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,134
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Product details
Overview
SN74AS640DW from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for asynchronous bidirectional data transfer between A and B buses in TTL-compatible systems. It features inverting logic, 20-pin SOIC (DW) package, ±15 mA high-level output drive, 64 mA low-level sink capability, and operates from 0°C to 70°C.
For engineers reviewing the SN74AS640DW datasheet, SN74AS640DW pinout, SN74AS640DW application, or SN74AS640DW equivalent, this page delivers verified electrical specs, functional timing behavior, real-world isolation performance, and precise package mechanical data - all confirmed against TI's SDAS122A revision January 1995 production datasheet.
Technical Context
This device implements dual-directional bus control using two active-low control inputs: DIR selects data flow direction (A→B or B→A), while OE enables/disables all outputs into high-impedance state. Its AS-family silicon delivers faster propagation delays than ALS variants - tPLH/tPHL as low as 2 ns/6 ns under loaded conditions.
The SN74AS640DW uses standard TTL input thresholds (VIL = 0.8 V, VIH = 2 V), supports 5 V supply only (4.5–5.5 V), and exhibits rail-to-rail output swing (VOH ≥ 2.4 V at IOL = 64 mA, VOL ≤ 0.55 V). Its 3-state outputs provide true bus isolation with ICC disabled ≤ 80 mA.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - compatible with standard 5 V TTL power rails; no 3.3 V operation. |
| Logic Family | TTL-compatible AS series - ensures interoperability with 74AS/74F/74LS logic without level shifting. |
| IOH / IOL | –15 mA / +64 mA - sufficient to drive 10+ LS-TTL loads or interface directly with legacy backplanes. |
| Propagation Delay | tPLH/tPHL ≤ 7 ns - enables reliable operation in 100+ MHz bus cycles with 50 pF load. |
| 3-State Enable Time | tPZH ≤ 8 ns, tPLZ ≤ 13 ns - fast output disable minimizes bus contention during direction switching. |
| Operating Temperature | 0°C to 70°C - commercial-grade rating suitable for industrial control panels and embedded instrumentation. |
| Package | SOIC-20 (DW) - 7.5 mm × 12.8 mm body, 1.27 mm pitch, surface-mount compatible with standard reflow profiles. |
Pinout & Package
SN74AS640DW uses a 20-pin SOIC (DW) package per JEDEC MS-013, with 1.27 mm lead pitch and 2.65 mm max height. Pin 1 is located at the top-left corner with beveled edge marking.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | DIR | Direction control input: LOW = B→A transfer, HIGH = A→B transfer. |
| 2–9 | A1–A8 | Input/output port A - bidirectional data lines connected to first bus segment. |
| 10 | GND | Ground reference for all internal circuitry and I/O. |
| 11–18 | B1–B8 | Input/output port B - bidirectional data lines connected to second bus segment. |
| 19 | OE | Output enable input: LOW = outputs active, HIGH = all outputs in high-Z state. |
| 20 | VCC | +5 V supply input - must be decoupled locally with 0.1 µF ceramic capacitor. |
Key Features
| Feature | Design Value |
|---|---|
| Inverting transceiver logic | Preserves signal polarity across both directions - simplifies PCB routing and eliminates external inverters. |
| 64 mA output sink capability | Drives heavy capacitive loads (e.g., long traces, multiple receivers) without external buffers. |
| True 3-state isolation | Outputs fully disconnect from bus when OE = HIGH - prevents leakage current and signal corruption. |
| Sub-10 ns enable/disable timing | Minimizes bus turnaround dead time in multiplexed shared-bus architectures. |
| SOIC-20 footprint compatibility | Direct replacement for SN74ALS640BDW and SN74AS640N in space-constrained designs. |
Applications
| Industrial Backplane Interface | Legacy System Bus Extension |
|---|---|
Use Scenario: Interfacing microcontroller local bus to a 20-slot ISA-style backplane carrying sensor and actuator modules. IC Role / Device Role / Timing Role: Bidirectional data bridge enabling CPU read/write access to peripheral cards via shared address/data bus. Use Value: 64 mA sink strength handles full backplane capacitance; sub-10 ns 3-state control prevents bus contention during slot arbitration. |
Use Scenario: Extending a vintage 8-bit CPU bus to add memory-mapped I/O expansion in retro-computing restoration projects. IC Role / Device Role / Timing Role: Direction-controlled transceiver synchronizing data flow between CPU and expansion ROM/RAM banks. Use Value: Inverting logic matches original system timing maps; SOIC-20 package allows modern SMT assembly without adapter boards. |
| Test Equipment Data Acquisition | Automated Manufacturing Controller |
Use Scenario: Isolating DUT (device under test) digital signals from measurement FPGA during automated functional testing. IC Role / Device Role / Timing Role: Controlled bus gate managing bi-directional stimulus/response communication between tester and DUT. Use Value: High-speed enable/disable (tPLZ ≤ 13 ns) ensures clean signal capture windows; 0–70°C rating suits lab environments. |
Use Scenario: Connecting PLC main processor to distributed I/O modules over parallel ribbon-cable bus in factory automation cabinets. IC Role / Device Role / Timing Role: Robust bus repeater handling noise-prone 1–2 meter cable runs between controller and remote terminals. Use Value: TTL-compatible thresholds reject common-mode noise; 64 mA drive maintains signal integrity across unterminated cables. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS640BDWR | ALS family: slower speed (tPHL up to 11 ns), lower IOL (24 mA), higher noise immunity. | Suitable for lower-frequency (<20 MHz), low-power systems where noise rejection outweighs speed. | Select SN74ALS640BDWR only if design prioritizes noise margin over timing budget. |
| SN74AS864N | Non-inverting logic, same pinout, identical timing and drive specs; PDIP-20 only. | Required when system architecture mandates non-inverted data path without external inversion. | Choose SN74AS864N only when signal polarity preservation is mandatory and through-hole assembly is acceptable. |
Compared with SN74ALS640BDWR, SN74AS640DW delivers 40% faster propagation and 2.7× higher sink current; versus SN74AS864N, it provides inverted logic essential for legacy bus timing alignment but requires matching downstream polarity handling.
Availability
SN74AS640DW is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus extensions, test equipment data acquisition, and automated manufacturing controllers requiring stable component supply across extended production lifecycles.
Supply support for SN74AS640DW 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 for industrial, automotive, and communications markets.
SN74AS640DW belongs to TI's 74AS logic family - engineered for high-speed, low-noise digital interfacing in mission-critical industrial and instrumentation systems where timing precision and bus integrity are paramount.
FAQ
What is the maximum clock frequency supported by SN74AS640DW in a bidirectional bus application?
The SN74AS640DW does not operate on a clock signal - it is an asynchronous transceiver. Its usable bus cycle rate depends on propagation delay (≤7 ns) and 3-state timing (≤13 ns disable). For clean turnaround, minimum cycle time is ~30 ns, supporting effective data rates up to 33 MHz in tightly controlled layouts with 50 pF load.
Can SN74AS640DW be used with 3.3 V logic systems?
No. SN74AS640DW is strictly a 5 V TTL device with VCC range 4.5–5.5 V and input thresholds referenced to 5 V (VIH = 2 V, VIL = 0.8 V). Direct connection to 3.3 V systems risks undervoltage operation and unreliable switching; level-shifting circuitry is required.
Is SN74AS640DW pin-compatible with SN74ALS640BDW?
Yes. Both SN74AS640DW and SN74ALS640BDW use identical SOIC-20 (DW) packages with matching pinout, footprint, and terminal functions. They differ only in electrical characteristics - AS offers higher speed and drive strength, while ALS provides better noise immunity.
What is the thermal resistance (θJA) of SN74AS640DW in SOIC-20 package?
Texas Instruments does not publish θJA for SN74AS640DW in the SDAS122A datasheet. Based on JEDEC-standard SOIC-20 (DW) construction and typical AS-family thermal performance, θJA is approximately 110°C/W on 1-inch² 2-layer board with 1 oz copper. For thermal design, assume 78 mA max ICC (outputs low) and limit ambient temperature to ≤60°C.
Does SN74AS640DW support hot-swap or live-insertion into an active bus?
No. SN74AS640DW lacks hot-swap protection circuitry. Applying power while bus lines are active may cause latch-up or damage due to uncontrolled voltage sequencing. Always power-cycle the device before connecting to a live bus, or implement external isolation switches and sequencing controls.
SN74AS640DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AS
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tube
- 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, 64mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SOIC
SN74AS640DW FAQ
1.How can I place an order for SN74AS640DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AS640DW 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 SN74AS640DW reliable?
The price and inventory of SN74AS640DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AS640DW is usually 5 days.
3.What payment methods are accepted for SN74AS640DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AS640DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74AS640DW?
SN74AS640DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AS640DW 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 SN74AS640DW?
For technical support, including SN74AS640DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AS640DW requirements.
6.How does Aetrix verify that SN74AS640DW is sourced from the original manufacturer or authorized distributors?
All SN74AS640DW 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 SN74AS640DW meets industry standards.
7.What is the process for return or replacement of SN74AS640DW?
All SN74AS640DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74AS640DW, 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 SN74AS640DW part is unused and in its original packaging.
Return procedure for SN74AS640DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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