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Texas Instruments SN74ALS638A-1DW
- Part No.:
- SN74ALS638A-1DW
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS638A-1DW.pdf
- Description:
- IC TXRX INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,674
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Product details
Overview
SN74ALS638A-1DW from Texas Instruments is an octal bus transceiver with inverting logic, designed for bidirectional communication between open-collector A-bus and 3-state B-bus systems. It features 20-pin SOIC (DW) packaging, 48 mA maximum low-level output current (IOL), operation from 0°C to 70°C, and supports asynchronous data flow controlled by DIR and OE pins - used in legacy industrial backplane and TTL-compatible bus interface applications.
For engineers reviewing the SN74ALS638A-1DW datasheet, SN74ALS638A-1DW pinout, SN74ALS638A-1DW application, or SN74ALS638A-1DW equivalent, key selection considerations include its -1 version's enhanced 48 mA IOL rating, open-collector A-side drive capability, 3-state B-side outputs, directional control architecture, and compatibility with 5 V TTL/ALS logic families.
Technical Context
The SN74ALS638A-1DW implements a dual-bus transceiver architecture with independent direction (DIR) and output-enable (OE) controls. Its A-bus outputs are open-collector with 7 V absolute max voltage tolerance, while B-bus outputs are 3-state with 5.5 V absolute max rating and –15 mA IOH capability.
It operates under 4.5 V to 5.5 V supply, delivers 2–12 ns propagation delay (A→B), 8–25 ns (B→A), and supports isolation via OE high. The -1 variant specifically increases guaranteed IOL from 24 mA to 48 mA at VCC = 4.75–5.25 V - a critical distinction for driving heavier open-collector loads.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Inverting octal bus transceiver with DIR/OE control for bidirectional A↔B data flow |
| Supply Voltage | 4.5 V to 5.5 V - compatible with standard 5 V TTL/ALS systems |
| IOL (A/B ports) | 48 mA (–1 version only, at VCC = 4.75–5.25 V) - enables direct drive of multiple 74-series inputs or pull-up networks |
| VOL (A/B ports) | 0.35 V max at IOL = 48 mA - ensures robust low-level noise margin under heavy load |
| Propagation Delay | 2–12 ns (A→B), 8–25 ns (B→A) - supports >40 MHz bus toggle rates in short-trace configurations |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade industrial control and instrumentation environments |
| Package | 20-pin SOIC (DW), RoHS-compliant, moisture sensitivity level 1 - suitable for surface-mount reflow assembly |
Pinout & Package
SN74ALS638A-1DW uses a 20-pin plastic small-outline integrated circuit (SOIC) package (DW), 7.5 mm wide, with 1.27 mm pitch and gull-wing leads. Pin 1 is located at top-left corner (Q1 quadrant), marked by beveled edge or dot.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction control input | Low = B-to-A data transfer; High = A-to-B data transfer |
| 2–9 (A1–A8) | A-bus I/O terminals | Open-collector outputs; require external pull-ups; tolerate up to 7 V |
| 10 (GND) | Ground reference | Power return for all internal logic and I/O stages |
| 11 (VCC) | Positive supply | 4.5–5.5 V DC supply for ALS logic core and output drivers |
| 12–19 (B1–B8) | B-bus I/O terminals | 3-state outputs; driven high/low or high-impedance per OE/DIR state |
| 20 (OE) | Output enable input | Low = outputs active; High = all outputs disabled (A open, B high-Z) |
Key Features
| Feature | Design Value |
|---|---|
| Inverting logic function | Ensures signal polarity consistency across A→B and B→A paths without external inversion |
| 48 mA IOL (-1 version) | Supports direct connection to 10+ standard TTL inputs or 20+ ALS inputs without buffer amplification |
| Asymmetric bus interface | Enables interoperability between legacy open-collector buses (e.g., I²C-like, interrupt lines) and modern 3-state data buses |
| Independent DIR and OE control | Allows dynamic bus arbitration: OE disables both directions simultaneously; DIR selects flow direction while enabled |
| ALS logic family | Delivers 2× speed and 50% lower power vs. standard LS, with improved noise immunity over temperature |
Applications
| Industrial Backplane Interface | Legacy System Bus Extension |
|---|---|
|
Use Scenario: Interfacing microcontroller local bus to a multi-slot industrial backplane with open-collector interrupt lines and 3-state data lanes. IC Role / Device Role / Timing Role: SN74ALS638A-1DW acts as bidirectional level- and topology-adapting transceiver, translating between MCU's 3-state data bus and backplane's open-collector control signals. Use Value: Eliminates need for discrete transistor arrays or dual buffers; 48 mA IOL drives long backplane traces with multiple stubs while maintaining <0.5 V VOL. |
Use Scenario: Extending address/data bus between two vintage 8-bit CPU boards using different physical layer conventions (one uses open-collector strobes, the other uses 3-state drivers). IC Role / Device Role / Timing Role: SN74ALS638A-1DW serves as protocol-transparent bus repeater, isolating sections and regenerating signals with sub-12 ns A→B delay. Use Value: Preserves timing integrity across extended bus segments; OE-controlled isolation prevents contention during board hot-swap or reset sequences. |
| Test Equipment Signal Routing | TTL-Compatible Logic Analyzer Front-End |
|
Use Scenario: Configurable signal routing matrix in automated test equipment where DUT interfaces vary between open-collector and 3-state protocols. IC Role / Device Role / Timing Role: SN74ALS638A-1DW functions as programmable bus coupler, with DIR/OE controlled by FPGA to route stimulus/response paths dynamically. Use Value: Single-component solution replaces multiple discrete gates and drivers; 20-pin SOIC footprint simplifies PCB layout and reduces interconnect skew. |
Use Scenario: Input conditioning stage for a logic analyzer capturing signals from mixed-technology systems (e.g., 74ALS control lines alongside 74AS data lines). IC Role / Device Role / Timing Role: SN74ALS638A-1DW provides impedance-matched, noise-immune signal acquisition on A-bus (open-collector) while presenting clean 3-state outputs to analyzer sampling logic. Use Value: VOL ≤ 0.35 V at 48 mA ensures reliable low-level detection; 7 V A-port tolerance protects against overshoot on long 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 |
|---|---|---|---|
| SN74ALS639A-1DW | True (non-inverting) logic function; otherwise identical electrical specs and pinout | Required when signal polarity must be preserved end-to-end (e.g., address bus extension) | Select SN74ALS639A-1DW only if inverting behavior of SN74ALS638A-1DW conflicts with system-level logic design |
| SN74AS638A-1DW | Faster propagation (2–7 ns A→B), higher ICC (75 mA max), 64 mA IOL, but wider VOL range (0.35–0.55 V) | Better suited for high-speed backplanes (>25 MHz) where ALS speed is insufficient | Choose SN74AS638A-1DW when timing budget demands sub-10 ns A→B delay and power dissipation is acceptable |
Compared with SN74ALS638A-1DW, SN74ALS639A-1DW preserves signal polarity at identical drive strength and timing, while SN74AS638A-1DW trades higher power and cost for significantly faster switching - making the original optimal for cost-sensitive, moderate-speed industrial interfaces requiring inverting logic.
Availability
SN74ALS638A-1DW is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus extensions, and test equipment signal routing requiring stable component supply, long-term obsolescence management, and RoHS-compliant SOIC packaging.
Supply support for SN74ALS638A-1DW 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 with broad industrial, automotive, and communications reach.
The SN74ALS638A-1DW belongs to TI's legacy 74ALS logic family, engineered for high-speed, low-power TTL-compatible digital interfacing in industrial control, instrumentation, and computer peripheral systems.
FAQ
What is the key functional difference between SN74ALS638A-1DW and SN74ALS639A-1DW?
The SN74ALS638A-1DW implements inverting logic: data transferred from A to B or B to A is complemented. In contrast, SN74ALS639A-1DW performs true (non-inverting) transfer. Both share identical pinout, package, supply range, temperature rating, and 48 mA IOL specification - making them drop-in replacements except for signal polarity requirements. SN74ALS638A-1DW is selected when system-level logic demands inversion across the bus interface.
Does SN74ALS638A-1DW support 3.3 V operation?
No, SN74ALS638A-1DW is specified only for 4.5 V to 5.5 V supply operation and is not characterized for 3.3 V use. Its input thresholds (VIH = 2 V min, VIL = 0.8 V max) and output drive strength assume 5 V rail conditions. Attempting 3.3 V operation may result in marginal noise margins, undefined switching behavior, or failure to meet VOL/VOL specifications - use TI's 74LVC or 74AVC series for 3.3 V–5 V translation.
What does the "-1" suffix indicate in SN74ALS638A-1DW?
The "-1" suffix denotes the enhanced-output-current variant of SN74ALS638A. While the base SN74ALS638A guarantees 24 mA IOL, the SN74ALS638A-1DW guarantees 48 mA IOL - but only when VCC is maintained between 4.75 V and 5.25 V. This doubling of sink current enables direct drive of heavier loads such as multiple TTL inputs, LED arrays, or long unterminated traces without external buffering.
Can SN74ALS638A-1DW interface between a 5 V microcontroller and a 12 V open-collector bus?
Yes - the A-bus I/O ports of SN74ALS638A-1DW tolerate up to 7 V absolute maximum, so direct connection to a 12 V bus requires external clamping (e.g., 5.1 V Zener + series resistor) to prevent damage. The device itself cannot withstand 12 V on A pins. For native 12 V open-collector interfacing, consider discrete level-shifting solutions or purpose-built high-voltage transceivers like TI's SN74LVCH16T245.
Is SN74ALS638A-1DW pin-compatible with SN74AS638A-1DW?
Yes, SN74ALS638A-1DW and SN74AS638A-1DW share identical 20-pin SOIC (DW) package, pin assignment, and functional block diagram. However, they differ electrically: SN74AS638A-1DW offers faster propagation (2–7 ns vs. 2–12 ns A→B), higher ICC (75 mA vs. 41 mA), and 64 mA IOL, but with reduced noise margin due to wider VOL range. Substitution is possible only if timing, power, and voltage margin requirements align.
SN74ALS638A-1DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- 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:
- 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
SN74ALS638A-1DW FAQ
1.How can I place an order for SN74ALS638A-1DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS638A-1DW 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 SN74ALS638A-1DW reliable?
The price and inventory of SN74ALS638A-1DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS638A-1DW is usually 5 days.
3.What payment methods are accepted for SN74ALS638A-1DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS638A-1DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS638A-1DW?
SN74ALS638A-1DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS638A-1DW 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 SN74ALS638A-1DW?
For technical support, including SN74ALS638A-1DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS638A-1DW requirements.
6.How does Aetrix verify that SN74ALS638A-1DW is sourced from the original manufacturer or authorized distributors?
All SN74ALS638A-1DW 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 SN74ALS638A-1DW meets industry standards.
7.What is the process for return or replacement of SN74ALS638A-1DW?
All SN74ALS638A-1DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS638A-1DW, 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 SN74ALS638A-1DW part is unused and in its original packaging.
Return procedure for SN74ALS638A-1DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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