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Texas Instruments SN74ALS639ADWR
- Part No.:
- SN74ALS639ADWR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS639ADWR.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,418
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Product details
Overview
SN74ALS639ADWR from Texas Instruments is an octal bus transceiver with true logic polarity, designed for bidirectional asynchronous communication between open-collector A-bus and 3-state B-bus systems. It features 20-pin SOIC (DW) package, 0°C to 70°C operating temperature, 24 mA low-level output current, and propagation delays as low as 2 ns (A→B) - used in legacy industrial backplane and parallel data interface designs.
For engineers reviewing the SN74ALS639ADWR datasheet, SN74ALS639ADWR pinout, SN74ALS639ADWR application, or SN74ALS639ADWR equivalent, key selection criteria include direction-control (DIR) and output-enable (OE) timing behavior, A-bus open-collector drive capability, B-bus 3-state voltage compatibility (VOH ≥ 2.4 V at –15 mA), and thermal reliability in extended-temperature industrial control modules.
Technical Context
This device implements dual-bus isolation using complementary control logic: DIR selects data flow direction (A→B or B→A), while OE independently disables both buses into high-impedance states. The A-bus outputs are open-collector with 7 V absolute max rating and –1.5 V input clamp voltage (VIK), enabling wired-OR interfacing with pull-up networks.
The B-bus outputs are 3-state TTL-compatible, specified for VOH ≥ 2.4 V at –15 mA and VOL ≤ 0.5 V at 24 mA, with enable/disable times (tPZH/tPZL) under 21 ns. Switching performance is characterized at CL = 50 pF, RL = 500 Ω (B-side), and RL = 680 Ω (A-side), confirming suitability for sub-25 ns synchronous bus cycles.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Function | True (non-inverting) bidirectional bus transceiver |
| Supply Voltage (VCC) | 4.5 V to 5.5 V - compatible with standard 5 V TTL systems |
| Operating Temperature | 0°C to 70°C - qualified for commercial/industrial ambient environments |
| A-Bus Output Type | Open-collector - supports wired-OR, level translation, and pull-up flexibility |
| B-Bus Output Type | 3-state - enables bus sharing without contention during disable |
| Max Propagation Delay | 30 ns (B→A path) - ensures timing margin in 33 MHz parallel bus systems |
| IOL (A/B ports) | 24 mA - sufficient to drive 10 LS-TTL loads or 20 ALS-TTL loads |
Pinout & Package
SN74ALS639ADWR uses a 20-pin SOIC (DW) package with 1.27 mm pitch, 7.6 mm body width, and 12.83 mm length per TI DW0020A outline. Pin 1 is marked by a beveled corner; device sits in gull-wing configuration with 0.4 mm lead thickness and 2.65 mm max height.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | Low = B→A data transfer; High = A→B data transfer |
| 2–9 (A1–A8) | A-Bus I/O Terminals | Open-collector outputs; require external pull-ups for logic HIGH |
| 10 (GND) | Ground Reference | Common return for all internal logic and I/O paths |
| 11–18 (B1–B8) | B-Bus I/O Terminals | 3-state outputs; driven HIGH/LOW or high-Z based on OE and DIR |
| 19 (OE) | Output Enable Input | Low = active; High = disables both A and B buses to high-Z |
| 20 (VCC) | Power Supply | 5 V nominal supply; must be decoupled locally to suppress switching noise |
Key Features
| Feature | Design Value |
|---|---|
| True logic polarity | Preserves signal phase across A↔B bus transfer - critical for parity and checksum integrity in legacy data paths |
| Asymmetric bus interface | Combines open-collector A-bus (wired-OR capable) with 3-state B-bus (TTL-compatible) - eliminates need for external bus buffers |
| Low propagation skew | tPLH/tPHL ≤ 12 ns (A→B) ensures simultaneous 8-bit transfer with <1 ns inter-bit skew |
| Robust input clamping | VIK = –1.5 V at –18 mA - protects against negative transients on shared bus lines |
| Control pin noise immunity | IIL ≤ –0.1 mA at VI = 0.4 V - prevents false triggering from EMI or crosstalk on DIR/OE |
Applications
| Industrial Backplane Interface | Legacy Parallel Printer Port |
|---|---|
|
Use Scenario: Isolating microcontroller address/data buses from multi-drop ISA-style backplanes with mixed-signal peripherals. IC Role / Device Role / Timing Role: Bidirectional level-shifting transceiver managing A-bus (open-collector control signals) and B-bus (3-state data lines) under DIR/OE arbitration. Use Value: Enables hot-plug-safe bus arbitration without external pull-up resistors on A-side and eliminates contention risk via OE-controlled 3-state B outputs. |
Use Scenario: Connecting 8-bit parallel data paths between PC LPT controllers and dot-matrix printers requiring open-collector handshake signaling. IC Role / Device Role / Timing Role: True-logic transceiver translating TTL-level printer status lines (BUSY, ACK) to open-collector format while driving data bits to printer's 3-state inputs. Use Value: Supports IEEE 1284-compliant bidirectional handshaking with guaranteed tPHL ≤ 12 ns (A→B) for reliable strobe-to-data setup timing. |
| EPROM Programming Adapter | Test Equipment Bus Extender |
|
Use Scenario: Interfacing 5 V microcontroller programmers with vintage EPROMs requiring open-collector programming voltage control and 3-state data latching. IC Role / Device Role / Timing Role: Direction-controlled bus coupler routing address bits (A-bus) to EPROM pins and reading data (B-bus) during verify cycles. Use Value: Delivers 24 mA sink current on A-bus to assert VPP control lines, while B-bus VOL ≤ 0.5 V at 24 mA ensures clean data sampling during read operations. |
Use Scenario: Extending GPIB or custom test bus segments across multiple PCBs in automated test equipment racks with isolated power domains. IC Role / Device Role / Timing Role: Isolation transceiver buffering control signals (DIR-driven) and data lanes (OE-gated) between master controller and peripheral modules. Use Value: Provides 30 ns B→A delay margin for 33 MHz test clock synchronization and withstands 7 V transient spikes on A-bus per MIL-STD-883 Class H testing. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS639AN | Same logic function and electrical specs, but in 20-pin PDIP (N) package with 300-mil width and through-hole mounting | Used where manual prototyping, socket-based debugging, or legacy board rework is required | Select SN74ALS639AN for breadboard validation or field-replaceable DIP sockets; SN74ALS639ADWR preferred for surface-mount production. |
| SN74AS639 | Faster propagation (B→A tPHL min = 2 ns vs. 5 ns), higher IOL (64 mA), but wider ICC range (95–154 mA vs. 30–50 mA) and reduced noise margin (VIH = 2 V only) | Suitable for high-speed bus extensions where timing closure is critical and power budget allows +40% supply current | Choose SN74AS639 only when sub-10 ns B→A delay is mandatory and system-level noise immunity has been verified. |
Compared with SN74ALS639AN and SN74AS639, the SN74ALS639ADWR delivers optimal balance of SOIC manufacturability, 24 mA drive strength, and 0.5 V VOL compliance - making it the default choice for cost-sensitive, thermally stable industrial backplane interfaces where 30 ns timing margins suffice.
Availability
SN74ALS639ADWR is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy parallel printer ports, EPROM programming adapters, and test equipment bus extenders requiring stable component supply across long-lifecycle embedded programs.
Supply support for SN74ALS639ADWR 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.
The SN74ALS639ADWR belongs to the 74ALS family of advanced low-power Schottky logic devices, engineered for reliable 5 V TTL interoperability in mission-critical industrial control and instrumentation systems.
FAQ
What is the maximum allowable voltage on the A-bus I/O ports of the SN74ALS639ADWR?
The SN74ALS639ADWR specifies an absolute maximum rating of 7 V for A-bus I/O ports. This allows safe operation with external pull-up resistors tied to 5.5 V or 7 V supplies, accommodating legacy systems with higher-voltage signaling domains. Exceeding this limit risks permanent damage to the open-collector output structure. Always reference the "Absolute Maximum Ratings" table in the SDAS123A datasheet for derating guidance.
Does the SN74ALS639ADWR support hot-swapping on live buses?
The SN74ALS639ADWR does not include built-in hot-swap protection circuitry. However, its open-collector A-bus outputs and 3-state B-bus outputs allow controlled insertion if OE is held HIGH (disabled) during connection, isolating both buses until system initialization completes. Real-world hot-swap reliability depends on external current limiting and slew-rate control - TI recommends verifying bus settling time and inrush behavior per application note SCBA005.
How does the DIR input affect data flow direction in the SN74ALS639ADWR?
In the SN74ALS639ADWR, the DIR input determines bidirectional data path: when DIR = LOW, data transfers from B-bus to A-bus (B→A); when DIR = HIGH, data flows from A-bus to B-bus (A→B). This control operates independently of OE - even with OE = HIGH (outputs disabled), DIR state remains valid and ready for immediate activation upon OE assertion. Timing is validated down to 2 ns tPLH/tPHL for A→B paths.
Can the SN74ALS639ADWR drive standard LS-TTL loads directly?
Yes, the SN74ALS639ADWR can drive up to 10 LS-TTL loads on its B-bus outputs, based on its IOH = –15 mA and VOL ≤ 0.5 V at 24 mA specifications. Its A-bus open-collector outputs require external pull-ups but can sink 24 mA - sufficient for 20 ALS-TTL or 10 LS-TTL inputs. For heavier loads, verify voltage drop across pull-up resistors using VIH = 2 V and VIL = 0.8 V thresholds per the recommended operating conditions table.
What is the significance of the "DWR" suffix in SN74ALS639ADWR?
The "DWR" suffix in SN74ALS639ADWR indicates a tape-and-reel packaging variant of the SOIC (DW) package - specifically, 25 units per tube with RoHS-compliant NiPdAu lead finish and moisture sensitivity level (MSL) 1 (unlimited floor life at ≤30°C/60% RH). This differs from the "DW" version, which denotes the same SOIC footprint but in tube packaging without tape-and-reel logistics. Both share identical electrical and thermal specifications.
SN74ALS639ADWR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Logic Type:
- Transceiver, Non-Inverting
- Number of Elements:
- 1
- Number of Bits per Element:
- 8
- Input Type:
- -
- Output Type:
- Open Collector, Push-Pull
- Current - Output High, Low:
- -, 24mA; 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-SOIC
SN74ALS639ADWR FAQ
1.How can I place an order for SN74ALS639ADWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS639ADWR 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 SN74ALS639ADWR reliable?
The price and inventory of SN74ALS639ADWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS639ADWR is usually 5 days.
3.What payment methods are accepted for SN74ALS639ADWR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS639ADWR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS639ADWR?
SN74ALS639ADWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS639ADWR 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 SN74ALS639ADWR?
For technical support, including SN74ALS639ADWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS639ADWR requirements.
6.How does Aetrix verify that SN74ALS639ADWR is sourced from the original manufacturer or authorized distributors?
All SN74ALS639ADWR 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 SN74ALS639ADWR meets industry standards.
7.What is the process for return or replacement of SN74ALS639ADWR?
All SN74ALS639ADWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS639ADWR, 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 SN74ALS639ADWR part is unused and in its original packaging.
Return procedure for SN74ALS639ADWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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