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Texas Instruments SN74ALS639AN
- Part No.:
- SN74ALS639AN
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74ALS639AN.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20DIP
- Quantity:
- Payment:
- Shipping:
Inventory:2,480
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Product details
Overview
SN74ALS639AN 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 interfaces. It features 20-pin PDIP packaging, operates from 0°C to 70°C, supports 5 V supply, and delivers 24 mA low-level output current on both buses - used in legacy industrial backplane and parallel bus isolation systems.
For engineers reviewing the SN74ALS639AN datasheet, SN74ALS639AN pinout, SN74ALS639AN application, or SN74ALS639AN equivalent, key selection criteria include direction-control (DIR) and output-enable (OE) timing behavior, A-bus open-collector voltage tolerance up to 7 V, B-bus 3-state VOH/VOL specs at –15 mA/24 mA, and compatibility with ALS logic family noise margins and propagation delays.
Technical Context
This device implements dual-bus bidirectional data routing using separate control paths: DIR selects data flow direction (A→B or B→A), while OE enables/disables all outputs simultaneously. The A-bus outputs are open-collector with 7 V absolute max input voltage rating, enabling direct interface with higher-voltage buses or wired-OR configurations.
The B-bus outputs are 3-state with VOH ≥ 2.4 V at –15 mA and VOL ≤ 0.4 V at 24 mA under 4.5–5.5 V VCC, meeting standard TTL-compatible thresholds. Propagation delays range from 2 ns (A→B) to 30 ns (B→A) across temperature and load conditions, consistent with ALS family performance.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - ensures stable operation across standard 5 V ±10% power rails |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade industrial control and instrumentation environments |
| A-Bus Output Type | Open-collector - allows wired-AND logic, level translation up to 7 V, and direct connection to external pull-ups |
| B-Bus Output Type | 3-state - enables bus sharing without contention when OE is high |
| IOL (A/B ports) | 24 mA - sufficient to drive multiple TTL inputs or moderate capacitive loads (≤50 pF) |
| tPHL/tPLH (A→B) | 2 ns to 12 ns - supports high-speed parallel data transfer in synchronous backplane designs |
| VIH/VIL | 2.0 V / 0.8 V - compatible with standard TTL input thresholds for reliable signal recognition |
Pinout & Package
SN74ALS639AN uses a 20-pin plastic DIP (PDIP-N) package with 300-mil width, 0.1-inch lead pitch, and through-hole mounting. Pin 1 is marked by a notch or dot; the package is RoHS-compliant with NIPDAU lead finish and no MSL rating (through-hole reflow not applicable).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | Low = B→A data transfer; High = A→B data transfer - determines active bus path |
| 2–9 (A1–A8) | A-Bus Open-Collector I/O | Inputs/outputs tied to open-collector bus - require external pull-up resistors for logic HIGH |
| 10 (GND) | Ground Reference | Common return path for all internal circuitry and I/O current sinks |
| 11–18 (B1–B8) | B-Bus 3-State I/O | Tri-state outputs enabled only when OE = Low - electrically isolates bus when disabled |
| 19 (OE) | Output Enable Input | Low = outputs active; High = all outputs high-impedance - provides bus isolation control |
| 20 (VCC) | Power Supply | +5 V supply pin - must be decoupled locally with 0.1 µF ceramic capacitor |
Key Features
| Feature | Design Value |
|---|---|
| True logic polarity | Preserves signal phase during A↔B data transfer - eliminates need for external inversion in non-inverting bus architectures |
| Asymmetric bus interface | Combines open-collector A-bus (7 V tolerant) with 3-state B-bus (TTL-compatible) - enables mixed-voltage system interconnection |
| Low propagation delay asymmetry | A→B delay (2–12 ns) is faster than B→A (10–30 ns) - optimizes timing-critical upstream data paths |
| Control-input noise immunity | VIH = 2.0 V / VIL = 0.8 V with 0.4 V hysteresis margin - rejects common-mode noise in electrically noisy industrial enclosures |
| Output disable isolation | ICC < 30 mA when OE = High - minimizes standby power and prevents bus leakage during idle states |
Applications
| Industrial Backplane Interface | Legacy Parallel Printer Port |
|---|---|
|
Use Scenario: Isolating microcontroller address/data buses from multi-drop industrial backplanes with mixed-voltage peripherals. IC Role / Device Role / Timing Role: Bidirectional bus transceiver managing A-bus (open-collector sensor bus) ↔ B-bus (MCU 3-state data lines) communication under DIR/OE control. Use Value: Enables robust noise-immune communication via open-collector A-bus while maintaining TTL-compatible B-bus signaling - critical for deterministic timing in PLC I/O modules. |
Use Scenario: Buffering and isolating Centronics-style parallel printer port signals between host controller and peripheral. IC Role / Device Role / Timing Role: True-logic octal transceiver translating bidirectional STROBE, ACK, BUSY, and DATA lines with independent OE control per direction. Use Value: Supports hot-plug-safe bus isolation and meets IEEE 1284 timing margins with sub-12 ns A→B propagation - essential for reliable legacy printer handshaking. |
| EPROM Programming Adapter | Test Equipment Bus Extender |
|
Use Scenario: Interfacing 5 V microcontroller programmers with 12 V EPROM address/data buses during in-circuit programming sequences. IC Role / Device Role / Timing Role: Level-shifting transceiver where A-bus connects to EPROM (open-collector, 12 V tolerant) and B-bus connects to MCU (3-state, 5 V). Use Value: A-bus 7 V absolute max rating allows safe clamping of 12 V programming pulses via external Zener networks - prevents damage during VPP transitions. |
Use Scenario: Extending digital test bus segments across modular rack-mounted instruments with isolated ground domains. IC Role / Device Role / Timing Role: Direction-controlled bus repeater synchronizing control/status signals between master controller and remote measurement modules. Use Value: DIR-selectable data flow and OE-gated isolation eliminate ground loop coupling while preserving nanosecond-level timing integrity across 1 m cable runs. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bidirectional bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS638AN | Inverting logic polarity vs. SN74ALS639AN's true logic - requires external inversion or firmware compensation | Suitable where signal inversion is acceptable or already compensated in system design | Select SN74ALS638AN only if inverting behavior aligns with existing bus protocol handshake logic |
| SN74AS639N | Faster propagation (B→A min 5 ns vs. 10 ns) and higher drive (64 mA IOL) but increased ICC (up to 154 mA) | Better suited for high-speed, low-capacitance backplanes requiring tighter timing margins | Choose SN74AS639N when speed outweighs power budget constraints and board layout supports AS-family noise mitigation |
Compared with SN74ALS639AN, SN74ALS638AN offers identical packaging and drive strength but inverts data - adding design complexity unless required. SN74AS639N improves speed and current capability at the cost of higher supply current and stricter noise control requirements - making it optimal for performance-critical upgrades rather than drop-in replacements.
Availability
SN74ALS639AN is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy parallel port adapters, EPROM programming fixtures, and modular test equipment requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS639AN 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.
SN74ALS639AN belongs to TI's legacy ALS (Advanced Low-Power Schottky) logic family, engineered for balanced speed-power trade-offs in commercial-temperature industrial control and instrumentation systems.
FAQ
What is the maximum allowable voltage on the A-bus pins of SN74ALS639AN?
The A-bus I/O ports of SN74ALS639AN tolerate up to 7 V per absolute maximum ratings - enabling safe interface with 5 V, 12 V, or other higher-voltage open-collector buses when used with appropriate external pull-up resistors and clamping diodes. This rating applies regardless of VCC state and is validated across the full 0°C to 70°C operating range.
Does SN74ALS639AN support hot-swap or live-insertion on the B-bus?
SN74ALS639AN supports controlled hot-swap operation on the B-bus when OE is held high during insertion - placing all B-bus outputs in high-impedance state and preventing bus contention. However, A-bus pins remain active unless externally isolated, so full live-insertion requires additional circuitry such as series resistors or dedicated hot-swap controllers alongside SN74ALS639AN.
Can SN74ALS639AN be used with 3.3 V logic systems?
SN74ALS639AN is not 3.3 V compatible: its minimum VCC is 4.5 V, VIH is 2.0 V (not 3.3 V–referenced), and B-bus VOH specification assumes 5 V supply. Direct connection to 3.3 V systems risks undriven outputs or logic misreads; level-shifting buffers or voltage translators must be used between SN74ALS639AN and 3.3 V devices.
What is the function of the DIR pin on SN74ALS639AN, and how does it interact with OE?
The DIR pin on SN74ALS639AN controls data direction: DIR = Low enables B→A transfer, DIR = High enables A→B transfer. OE operates independently - when OE = High, all outputs go high-impedance regardless of DIR state, fully isolating both buses. This dual-control architecture allows precise sequencing of bus enablement and direction setting in complex backplane protocols.
Is SN74ALS639AN pin-compatible with SN74ALS639ADW?
Yes - SN74ALS639AN (PDIP-N) and SN74ALS639ADW (SOIC-DW) share identical 20-pin functional pinout and electrical specifications. The only differences are package type (through-hole vs. surface-mount), thermal characteristics, and mechanical dimensions; no PCB redesign is needed when migrating between them beyond footprint adaptation.
SN74ALS639AN Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-DIP (0.300", 7.62mm)
- Packaging:
- Bulk
- Product Status:
- Active
- 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:
- Through Hole
- Supplier Device Package:
- 20-PDIP
SN74ALS639AN FAQ
1.How can I place an order for SN74ALS639AN through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS639AN 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 SN74ALS639AN reliable?
The price and inventory of SN74ALS639AN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS639AN is usually 5 days.
3.What payment methods are accepted for SN74ALS639AN?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS639AN transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS639AN?
SN74ALS639AN orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS639AN 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 SN74ALS639AN?
For technical support, including SN74ALS639AN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS639AN requirements.
6.How does Aetrix verify that SN74ALS639AN is sourced from the original manufacturer or authorized distributors?
All SN74ALS639AN 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 SN74ALS639AN meets industry standards.
7.What is the process for return or replacement of SN74ALS639AN?
All SN74ALS639AN units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS639AN, 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 SN74ALS639AN part is unused and in its original packaging.
Return procedure for SN74ALS639AN:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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