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Texas Instruments SN74ALS640B-1NS
- Part No.:
- SN74ALS640B-1NS
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.209", 5.30mm Width)
- Datasheet:
-
SN74ALS640B-1NS.pdf
- Description:
- PROTOTYPE
- Quantity:
- Payment:
- Shipping:
Inventory:3,123
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Product details
Overview
SN74ALS640B-1NS 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, direction control (DIR), output-enable (OE), and supports 48 mA low-level output current (IOL) at VCC = 4.75–5.25 V - a key differentiator of the "-1" variant. Used in legacy industrial backplane and memory expansion interfaces.
For engineers reviewing the SN74ALS640B-1NS datasheet, SN74ALS640B-1NS pinout, SN74ALS640B-1NS application, or SN74ALS640B-1NS equivalent, this page delivers verified electrical specs, package mapping to SOP-20 (NS), functional truth table behavior, thermal limits (0°C to 70°C), and direct alternative part comparisons grounded in TI's official SDAS122A documentation.
Technical Context
This device implements dual 8-bit bidirectional bus interface logic with independent DIR and OE controls: DIR selects data flow direction (A→B or B→A), while OE places all outputs in high-impedance state for bus isolation. Its ALS (Advanced Low-Power Schottky) process ensures compatibility with standard TTL voltage thresholds (VIH = 2 V, VIL = 0.8 V) and reduced power consumption versus earlier LS families.
Switching performance is characterized under CL = 50 pF, R1/R2 = 500 Ω: propagation delays range from 2 ns (min) to 11 ns (max) for A↔B paths, and enable/disable times (tPZH/tPLZ) are specified up to 21 ns max - critical for synchronous bus arbitration timing budgets in legacy computing systems.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - operates reliably across standard TTL supply tolerance without regulation overhead. |
| IOL (–1 version) | 48 mA - enables direct drive of multiple TTL loads or termination-resistor networks without external buffers. |
| VOH / VOL | VOH ≥ 2.4 V @ IOH = –12 mA; VOL ≤ 0.4 V @ IOL = 24 mA - meets TTL output swing requirements for noise margin compliance. |
| tPLH / tPHL | 2–11 ns - defines maximum data valid window for 8-bit parallel transfers at >30 MHz effective bus rates. |
| Operating Temp | 0°C to 70°C - qualified for commercial-grade embedded control and instrumentation applications. |
| Package | SOP-20 (NS) - surface-mount footprint compatible with automated assembly; 7.6 mm × 13.0 mm body, 1.27 mm pitch. |
| Logic Type | Inverting - output polarity inversion must be accounted for in bus protocol layer design. |
Pinout & Package
SOP-20 (NS) package: 7.6 mm × 13.0 mm body, 1.27 mm lead pitch, 2.65 mm max height, RoHS-compliant NiPdAu lead finish, MSL Level-1.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | DIR | Direction control input: LOW enables B→A data flow; HIGH enables A→B flow. |
| 2–9 | A1–A8 | Input/output port A - connects to primary system bus; driven or sensed depending on DIR state. |
| 10 | GND | Ground reference for all logic and I/O operations. |
| 11–18 | B1–B8 | Input/output port B - connects to secondary bus or peripheral; bidirectional per DIR setting. |
| 19 | OE | Output-enable active-low: LOW enables transceiver; HIGH forces all A/B pins into high-Z state. |
| 20 | VCC | Positive supply input: must be decoupled locally to suppress switching noise on shared 5 V rail. |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional 8-bit bus interface | Enables single-chip isolation between two 8-bit data paths - reduces PCB trace count vs discrete gate solutions. |
| 48 mA IOL (–1 version) | Supports fan-out to ≥10 standard TTL inputs or direct termination into 50 Ω lines without level-shifting circuitry. |
| 3-state outputs with OE control | Allows dynamic bus sharing among multiple masters/slaves via centralized enable sequencing. |
| ALS logic family | Delivers 2× speed and 50% lower power than standard LS, with full TTL voltage compatibility. |
| Inverting data path | Ensures predictable signal polarity when cascading with non-inverting peripherals - simplifies timing analysis. |
Applications
| Industrial Backplane Interface | Legacy Memory Expansion |
|---|---|
Use Scenario: Isolating CPU address/data bus from modular I/O card slots in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional bus transceiver managing A→B (CPU→card) and B→A (card→CPU) transfers under DIR/OE arbitration. Use Value: Eliminates need for separate unidirectional drivers and tri-state logic gates - cuts component count by 3× per bus segment. |
Use Scenario: Extending 8-bit data bus between mainboard and plug-in RAM modules in early microcomputer systems. IC Role / Device Role / Timing Role: Direction-controlled data conduit enabling read/write cycles across 200+ mm backplane traces. Use Value: 11 ns max propagation delay ensures setup/hold timing closure at 8 MHz bus clock rates without added wait states. |
| Test Equipment Bus Arbitration | Embedded Controller Peripheral Bridge |
Use Scenario: Sharing a common test bus among multiple DUT interface boards in automated test fixtures. IC Role / Device Role / Timing Role: OE-gated isolation element preventing signal contention during parallel DUT access. Use Value: 24 ns max disable time (tPLZ) guarantees clean bus release before next board activation - avoids metastability. |
Use Scenario: Interfacing an 8-bit microcontroller GPIO port to external ADC/DAC chips with mismatched voltage thresholds. IC Role / Device Role / Timing Role: Level-translating buffer providing TTL-compatible drive strength to legacy analog peripherals. Use Value: 48 mA IOL drives 50 Ω coaxial cables directly - eliminates external line drivers in sensor acquisition subsystems. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS640BN | Same ALS logic, identical electrical specs, but in PDIP-20 (N) through-hole package. | Requires manual soldering or wave-solder process; unsuitable for high-density SMT layouts. | Select when prototyping on breadboards or repairing legacy through-hole systems where SOP rework is impractical. |
| SN74AS640N | AS-family variant: faster (6 ns max tPHL), higher IOL (64 mA), but increased ICC (78 mA vs 55 mA). | Higher power draw and EMI may require redesign of decoupling and layout in noise-sensitive environments. | Choose only when timing-critical paths demand sub-7 ns propagation - not for drop-in replacement due to power/thermal mismatch. |
Compared with SN74ALS640B-1NS, SN74ALS640BN offers identical functionality in through-hole form for repair or prototyping, while SN74AS640N trades higher speed and drive for significantly greater supply current and thermal load - requiring careful validation in thermally constrained SMT designs.
Availability
SN74ALS640B-1NS is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy memory expansion modules, and embedded controller peripheral bridges requiring stable component supply over extended production lifecycles.
Supply support for SN74ALS640B-1NS 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 broad industrial, automotive, and aerospace qualification.
SN74ALS640B-1NS belongs to TI's legacy TTL-compatible logic portfolio, engineered specifically for robust, low-power bidirectional bus interfacing in commercial-temperature embedded systems and retro-computing infrastructure.
FAQ
What is the maximum operating temperature range for SN74ALS640B-1NS?
The SN74ALS640B-1NS is characterized for operation from 0°C to 70°C, consistent with commercial-grade TI logic devices. This range is explicitly defined in the SDAS122A datasheet under "recommended operating conditions" and validated across production lots. Exceeding 70°C risks parametric shift in VOH/VOL and increased ICC, potentially violating TTL interface margins. For extended temperature operation, consider the military-grade SN54ALS640B (–55°C to 125°C), though it lacks the "-1" IOL enhancement.
Does SN74ALS640B-1NS support pin-to-pin replacement with SN74ALS640BN?
Yes, SN74ALS640B-1NS and SN74ALS640BN share identical pinout, logic function, and electrical specifications - differing only in package type (SOP-20 vs PDIP-20). The SOP-20 (NS) and PDIP-20 (N) footprints are mechanically incompatible, so PCB redesign is required. However, no changes to schematic, firmware, or timing analysis are needed when migrating between these variants, as all timing parameters, voltage thresholds, and drive strengths match exactly per TI's SDAS122A documentation.
What is the significance of the "-1" suffix in SN74ALS640B-1NS?
The "-1" suffix in SN74ALS640B-1NS denotes enhanced low-level output current capability: IOL is rated at 48 mA (vs 24 mA for standard SN74ALS640B), but only when VCC is maintained between 4.75 V and 5.25 V. This specification is explicitly called out in the SDAS122A datasheet's "recommended operating conditions" table and confirmed in the "electrical characteristics" section. It enables direct driving of heavier capacitive or resistive loads without external buffering - a critical advantage in legacy bus termination scenarios.
Can SN74ALS640B-1NS be used in place of SN74AS640N?
No, SN74ALS640B-1NS is not a direct substitute for SN74AS640N. While both are octal 3-state transceivers in 20-pin packages, the AS family has faster propagation delays (6 ns max vs 11 ns), higher IOL (64 mA vs 48 mA), and significantly greater supply current (78 mA vs 55 mA). Substituting SN74ALS640B-1NS for SN74AS640N may cause timing violations in high-speed designs, and replacing SN74AS640N with SN74ALS640B-1NS risks marginal setup/hold timing in systems relying on AS-speed margins. Functional equivalence does not imply interchangeability.
What are the absolute maximum ratings for SN74ALS640B-1NS?
The absolute maximum ratings for SN74ALS640B-1NS are: supply voltage (VCC) ≤ 7 V; input voltage (VI) ≤ 7 V on control pins, ≤ 5.5 V on I/O ports; operating free-air temperature ≤ 70°C; storage temperature between –65°C and 150°C. These values are extracted verbatim from the SDAS122A datasheet "absolute maximum ratings" table. Exceeding any of these limits - even momentarily - may cause permanent damage. Designers must ensure transient suppression, proper decoupling, and thermal derating to maintain reliability within these boundaries.
SN74ALS640B-1NS Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-SOIC (0.209", 5.30mm 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, 24mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SO
SN74ALS640B-1NS FAQ
1.How can I place an order for SN74ALS640B-1NS through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS640B-1NS 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 SN74ALS640B-1NS reliable?
The price and inventory of SN74ALS640B-1NS are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS640B-1NS is usually 5 days.
3.What payment methods are accepted for SN74ALS640B-1NS?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS640B-1NS transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS640B-1NS?
SN74ALS640B-1NS orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS640B-1NS 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 SN74ALS640B-1NS?
For technical support, including SN74ALS640B-1NS datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS640B-1NS requirements.
6.How does Aetrix verify that SN74ALS640B-1NS is sourced from the original manufacturer or authorized distributors?
All SN74ALS640B-1NS 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 SN74ALS640B-1NS meets industry standards.
7.What is the process for return or replacement of SN74ALS640B-1NS?
All SN74ALS640B-1NS units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS640B-1NS, 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 SN74ALS640B-1NS part is unused and in its original packaging.
Return procedure for SN74ALS640B-1NS:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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