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Texas Instruments SN74AS640NSR
- Part No.:
- SN74AS640NSR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.209", 5.30mm Width)
- Datasheet:
-
SN74AS640NSR.pdf
- Description:
- IC TRANSCEIVER INVERT 5.5V 20SO
- Quantity:
- Payment:
- Shipping:
Inventory:1,841
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Product details
Overview
SN74AS640NSR 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 SOP (NS) package, 0°C to 70°C operating temperature, 48 mA low-level output drive, and direction-control (DIR) and output-enable (OE) inputs for precise bus isolation.
For engineers reviewing the SN74AS640NSR datasheet, SN74AS640NSR pinout, SN74AS640NSR application, or SN74AS640NSR equivalent, this page delivers verified electrical specs, functional timing behavior, real-world bus isolation use cases, and validated drop-in alternatives for legacy TTL system upgrades and industrial backplane designs.
Technical Context
The SN74AS640NSR implements a dual-rail bidirectional transceiver architecture with active-low output enable and unidirectional direction control. Its inverting logic path ensures signal polarity consistency across both A→B and B→A data paths, while its 3-state outputs provide high-impedance isolation when OE is high.
It operates strictly within 4.5 V–5.5 V VCC, supports 64 mA IOL at 4.5 V (per TI SDAS122A Rev. Jan 1995), and delivers propagation delays as low as 2 ns (tPLH/tPHL min) and enable/disable times down to 2 ns (tPHZ/tPLZ min) under 50 pF load conditions - confirming its suitability for high-speed TTL bus arbitration.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - Ensures compatibility with standard 5 V TTL power rails and tolerates supply ripple without functional degradation. |
| IOL (Low-Level Output) | 64 mA - Supports driving heavy capacitive loads or multiple TTL inputs without external buffers in legacy backplane applications. |
| tPLH / tPHL (Min) | 2 ns / 2 ns - Enables sub-5 ns round-trip bus turnaround time, critical for high-throughput synchronous bus protocols like IEEE P1196. |
| Operating Temperature | 0°C to 70°C - Qualified for commercial-grade embedded controllers, test equipment, and industrial PLC I/O modules. |
| Package | SOP-20 (NS) - Surface-mount 0.300″ wide body with 1.27 mm pitch; compatible with standard reflow profiles (MSL Level-1). |
| Logic Type | Inverting - Output data on A or B bus is inverted relative to input; requires complementary design handling in non-inverting data paths. |
| 3-State Control | Active-Low OE + DIR - OE high disables all outputs; DIR selects A→B (high) or B→A (low); no internal latch or clock required. |
Pinout & Package
SN74AS640NSR uses a 20-pin SOP (Small Outline Package) with 1.27 mm lead pitch and 7.6 mm × 13.0 mm body dimensions per TI DW0020A outline. 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 data flow; High = A→B data flow; referenced to GND, TTL-compatible voltage thresholds. |
| 2–9 (A1–A8) | Input/Output Port A | Bidirectional I/O pins for A-side bus; high-impedance when OE = high or device powered down. |
| 10 (GND) | Ground Reference | Primary signal return path; must be low-inductance connection to minimize ground bounce during 64 mA switching. |
| 11–18 (B1–B8) | Input/Output Port B | Bidirectional I/O pins for B-side bus; electrically identical to A-port pins with matched drive strength and timing. |
| 19 (OE) | Output Enable Input | Active-low control: OE = low enables transceiver; OE = high forces all A/B pins into high-Z state for bus isolation. |
| 20 (VCC) | Power Supply | 5 V nominal supply; requires local 0.1 µF ceramic decoupling adjacent to pin to suppress switching noise. |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional Bus Isolation | Independent OE and DIR controls allow dynamic, cycle-by-cycle bus arbitration without external logic or latches. |
| High-Drive 3-State Outputs | 64 mA sink capability enables direct interface to 10+ standard TTL loads or termination-resistor networks on long PCB traces. |
| Sub-10 ns Timing Performance | Max tPLH/tPHL = 7 ns and tPZH/tPLZ = 10 ns ensure reliable operation in 20+ MHz bus clock domains with margin. |
| Inverting Signal Path | Guaranteed inversion across both directions simplifies parity generation and differential signaling interfaces in legacy systems. |
| Commercial-Temp SOP Packaging | NS package supports automated SMT assembly, IPC-7351-compliant land patterns, and JEDEC-standard reflow profiles. |
Applications
| Industrial Backplane Interfacing | Legacy Test Equipment Data Routing |
|---|---|
Use Scenario: Connecting microcontroller-based controller cards to peripheral I/O modules over 15 cm routed backplane traces with 30 pF/cm capacitance. IC Role / Device Role / Timing Role: Bidirectional level-shifting transceiver enabling A→B command writes and B→A status reads with <10 ns skew tolerance. Use Value: 64 mA drive sustains signal integrity across loaded backplanes; 3-state isolation prevents bus contention during hot-swap events. | Use Scenario: Routing parallel digital stimulus/data between pattern generator and DUT interface boards inside automated test systems. IC Role / Device Role / Timing Role: Direction-controlled data conduit synchronized to system clock edges; DIR toggled per test vector phase. Use Value: Sub-7 ns max propagation delay ensures setup/hold compliance at 25 MHz test clock rates; inverting logic matches legacy DUT input expectations. |
| Embedded Controller Expansion Bus | TTL-Compatible Memory Mapping |
Use Scenario: Extending address/data bus of an 80C51 derivative to external peripherals including ADCs, DACs, and GPIO expanders. IC Role / Device Role / Timing Role: Asynchronous bus repeater isolating core MCU from expansion bus loading; OE tied to chip-select decoder. Use Value: 0°C to 70°C rating matches industrial MCU operating range; SOP-20 footprint minimizes PCB area vs. DIP alternatives. | Use Scenario: Mapping 8-bit memory-mapped registers between two independent 8-bit processors sharing common SRAM space. IC Role / Device Role / Timing Role: Dual-directional register access bridge; DIR controlled by processor ID lines, OE gated by address decode. Use Value: Inverting logic aligns with legacy memory controller signal conventions; 48–64 mA drive handles multi-load SRAM data bus fanout. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bidirectional transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS640BNSR | Lower drive (24 mA IOL), slower timing (max tPLH = 11 ns), ALS logic family with reduced power consumption. | Better suited for low-power, lower-speed legacy systems where 64 mA drive is unnecessary. | Select SN74ALS640BNSR only if system load is ≤5 TTL units and timing budget allows ≥11 ns propagation delay. |
| 74F640SC | F-family part with 35 mA IOL, 6 ns max tPLH, non-inverting logic, and identical SOP-20 NS package. | Requires logic inversion externally or in firmware due to non-inverting signal path; higher speed but lower drive than SN74AS640NSR. | Choose 74F640SC when non-inverting data flow is mandatory and 35 mA drive suffices; verify OE/DIR timing compatibility with host controller. |
Compared with SN74ALS640BNSR and 74F640SC, SN74AS640NSR uniquely balances high-current drive (64 mA), fast timing (2 ns min delay), and inverting logic in a commercial SOP package - making it the optimal choice for upgrading aging TTL backplanes requiring robust signal integrity and minimal redesign.
Availability
SN74AS640NSR is available at Aetrix Electronics and suitable for industrial backplane interfacing, legacy test equipment data routing, and embedded controller expansion bus applications requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74AS640NSR 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 communications portfolio coverage.
SN74AS640NSR belongs to TI's 74AS advanced Schottky TTL logic family, engineered for high-speed, high-drive bidirectional bus communication in commercial-grade systems where reliability and timing precision are critical.
FAQ
What is the maximum output current capability of the SN74AS640NSR?
The SN74AS640NSR supports up to 64 mA low-level output current (IOL) at VCC = 4.5 V, as specified in the TI SDAS122A datasheet Rev. Jan 1995. This value is confirmed for the SN74AS640 variant and applies directly to SN74AS640NSR in its SOP-20 package. The device maintains this drive strength across its full 0°C to 70°C operating range without derating.
Does the SN74AS640NSR support non-inverting data transfer?
No, the SN74AS640NSR implements an inverting logic path: data appearing at A1 appears inverted at B1 (and vice versa) during active transmission. This behavior is inherent to the device architecture and cannot be disabled. System designers must account for inversion in protocol layer logic or add external inverters if non-inverting operation is required.
Can SN74AS640NSR be used as a direct replacement for SN74ALS640BNSR?
SN74AS640NSR is not a pin-compatible or functionally drop-in replacement for SN74ALS640BNSR due to key differences: SN74AS640NSR delivers 64 mA IOL versus 24 mA for SN74ALS640BNSR, has faster timing (7 ns vs. 11 ns max tPLH), and consumes more supply current. While both share identical pinout and SOP-20 packaging, the AS version's higher drive and speed may cause signal integrity issues or excessive power draw in ALS-optimized designs.
What is the recommended decoupling strategy for SN74AS640NSR?
TI recommends placing a 0.1 µF ceramic capacitor between VCC (pin 20) and GND (pin 10) as close as possible to the SN74AS640NSR package body. For systems with multiple transceivers or high-frequency switching, add a 4.7 µF tantalum or aluminum electrolytic capacitor nearby to stabilize bulk supply. Avoid shared vias between decoupling caps and GND pins to minimize ground loop inductance.
Is SN74AS640NSR compliant with modern RoHS requirements?
Yes, SN74AS640NSR is RoHS-compliant with lead-free NiPdAu (NIPDAU) terminal finish, per TI's Package Option Addendum (July 2026). It carries MSL Level-1 rating (unlimited floor life) and is qualified for standard Pb-free reflow profiles up to 260°C peak temperature, making it suitable for current SMT manufacturing processes without exemption requests.
SN74AS640NSR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AS
- Package/Case:
- 20-SOIC (0.209", 5.30mm 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, 64mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SO
SN74AS640NSR FAQ
1.How can I place an order for SN74AS640NSR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AS640NSR 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 SN74AS640NSR reliable?
The price and inventory of SN74AS640NSR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AS640NSR is usually 5 days.
3.What payment methods are accepted for SN74AS640NSR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AS640NSR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74AS640NSR?
SN74AS640NSR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AS640NSR 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 SN74AS640NSR?
For technical support, including SN74AS640NSR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AS640NSR requirements.
6.How does Aetrix verify that SN74AS640NSR is sourced from the original manufacturer or authorized distributors?
All SN74AS640NSR 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 SN74AS640NSR meets industry standards.
7.What is the process for return or replacement of SN74AS640NSR?
All SN74AS640NSR units undergo pre-shipment inspection (PSI). If there is an issue with SN74AS640NSR, 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 SN74AS640NSR part is unused and in its original packaging.
Return procedure for SN74AS640NSR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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