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Texas Instruments SN74ALS638A-1DWR
- Part No.:
- SN74ALS638A-1DWR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS638A-1DWR.pdf
- Description:
- IC TXRX INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:4,181
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Product details
Overview
SN74ALS638A-1DWR from Texas Instruments is an octal bidirectional bus transceiver with inverting logic, open-collector A-bus outputs (48 mA IOL max), 3-state B-bus outputs, and dual active-low control inputs (DIR, OE) for asynchronous two-way communication between mixed-logic buses. It operates from 4.5 V to 5.5 V at 0°C to 70°C and is used in legacy industrial backplane and memory expansion interfaces.
For engineers reviewing the SN74ALS638A-1DWR datasheet, SN74ALS638A-1DWR pinout, SN74ALS638A-1DWR application, or SN74ALS638A-1DWR equivalent, key selection considerations include its -1 version's enhanced 48 mA A-bus sink capability, DW package thermal and layout constraints, direction-controlled data flow between open-collector and 3-state domains, and compatibility with ALS logic families in legacy TTL systems.
Technical Context
The SN74ALS638A-1DWR implements a dual-control bidirectional data path: DIR selects direction (A→B or B→A), while OE enables/disables both buses simultaneously. Its A-side uses open-collector outputs compatible with wired-OR and pull-up bus topologies; B-side uses 3-state outputs for high-impedance isolation when disabled.
It features asymmetric switching: A→B propagation delay is 2–12 ns, while B→A is slower (8–30 ns), reflecting internal asymmetry optimized for A-bus sink-heavy applications. The -1 variant increases guaranteed A-bus low-level output current to 48 mA under 4.75–5.25 V, distinguishing it from the standard SN74ALS638A (24 mA).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Function | Inverting octal bidirectional bus transceiver with DIR/OE controls |
| Supply Voltage | 4.5 V to 5.5 V - supports standard 5 V TTL/ALS systems with ±5% tolerance |
| A-Bus Output Type | Open-collector - enables wired-OR, level translation, and shared-bus arbitration |
| B-Bus Output Type | 3-state - provides high-impedance isolation when OE is high |
| Max A-Bus Sink Current | 48 mA (–1 version only, at VCC = 4.75–5.25 V) - drives heavy capacitive or resistive loads on legacy buses |
| Propagation Delay (A→B) | 2–12 ns - ensures fast forward-path timing in master-to-peripheral data transfers |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade industrial equipment environments |
Pinout & Package
SN74ALS638A-1DWR is housed in a 20-pin SOIC (DW) package, 7.5 mm wide, with 0.65 mm lead pitch and RoHS-compliant CU NIPDAU finish. Moisture sensitivity level is Level-1 (260°C peak reflow).
| 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; sink up to 48 mA each |
| 10 (GND) | Ground Reference | Power return for all logic and I/O circuits |
| 11–18 (B1–B8) | B-Bus I/O Terminals | 3-state outputs - high-impedance when OE = High |
| 19 (OE) | Output Enable Input | Active-low - disables both A and B outputs simultaneously |
| 20 (VCC) | Positive Supply | 5 V nominal supply; must be decoupled locally per best practice |
Key Features
| Feature | Design Value |
|---|---|
| Inverting Logic Path | Ensures signal polarity consistency across A↔B data flow without external inversion |
| 48 mA A-Bus Sink Capability (-1 version) | Supports driving multiple TTL inputs or long traces with high capacitive load |
| Dual Independent Bus Domains | Enables interconnection of open-collector (e.g., interrupt lines) and 3-state (e.g., data bus) subsystems |
| Asymmetric Propagation Timing | Optimized 2–12 ns A→B delay improves timing margin in host-initiated writes |
| Commercial Temperature Range | Validated operation from 0°C to 70°C - suitable for non-extended industrial enclosures |
Applications
| Industrial Backplane Interface | Legacy Memory Expansion |
|---|---|
Use Scenario: Interfacing microcontroller address/data buses to ISA-style peripheral slots with mixed open-collector control signals and 3-state data lanes. IC Role / Device Role / Timing Role: Bidirectional level- and topology-adaptive transceiver managing A→B address latching and B→A status reads under DIR control. Use Value: Eliminates discrete buffer arrays by integrating eight channels with independent direction and enable, reducing board area and interconnect complexity. |
Use Scenario: Extending 8-bit parallel EPROM/RAM data paths in vintage test equipment where A-bus drives pull-up-based control lines and B-bus connects to memory ICs. IC Role / Device Role / Timing Role: Inverting transceiver synchronizing read/write cycles between CPU and memory modules using OE-gated 3-state B outputs and open-collector A outputs for chip select decoding. Use Value: 48 mA A-bus sink strength reliably drives multiple memory chip enable inputs under worst-case VCC and temperature conditions. |
| Parallel Printer Port Controller | TTL-Based Diagnostic Bus |
Use Scenario: Managing bi-directional handshaking (STROBE, ACK, BUSY) and 8-bit data between MCU and parallel printer in embedded instrumentation. IC Role / Device Role / Timing Role: Direction-controlled transceiver routing MCU-generated strobes (A→B) and printer feedback signals (B→A) over shared physical lines. Use Value: Asymmetric B→A delay (8–30 ns) accommodates slower peripheral response while maintaining tight A→B timing for command issuance. |
Use Scenario: Isolating and routing diagnostic signals (e.g., fault flags, sensor alerts) across modular rack-mounted units with shared open-collector alarm bus and local 3-state monitoring bus. IC Role / Device Role / Timing Role: Fault-tolerant bus coupler enabling centralized polling (B→A) and distributed alerting (A→B) via DIR-selectable paths. Use Value: Open-collector A outputs allow wire-OR of multiple unit alarms; 3-state B outputs prevent contention during local diagnostics. |
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 |
|---|---|---|---|
| SN74ALS638ADWR | Standard version with 24 mA max A-bus IOL (vs. 48 mA in -1) | Limited drive strength for heavily loaded A-bus nodes | Select when load current ≤24 mA and cost optimization is prioritized |
| SN74ALS639A-1DWR | True (non-inverting) logic function; otherwise identical pinout, timing, and drive specs | Requires no external inversion for applications needing same-phase A↔B data | Choose when signal polarity preservation is required and system logic design avoids added inverters |
Compared with SN74ALS638ADWR, the SN74ALS638A-1DWR delivers double A-bus sink current for robustness in marginal bus conditions; compared with SN74ALS639A-1DWR, it provides inverted logic essential for interfacing with legacy control protocols requiring complemented handshake signals.
Availability
SN74ALS638A-1DWR is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy memory expansion systems, and parallel peripheral controllers requiring stable component supply across long-lifecycle production programs.
Supply support for SN74ALS638A-1DWR 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 SN74ALS638A-1DWR belongs to TI's legacy ALS (Advanced Low-Power Schottky) logic family, designed specifically for high-speed, low-power interoperability in 5 V TTL-compatible systems with stringent noise immunity and drive requirements.
FAQ
What is the key functional difference between SN74ALS638A-1DWR and the standard SN74ALS638ADWR?
The SN74ALS638A-1DWR guarantees a minimum A-bus low-level output current (IOL) of 48 mA when VCC is between 4.75 V and 5.25 V, whereas the standard SN74ALS638ADWR is rated for only 24 mA. This higher drive strength allows the SN74ALS638A-1DWR to reliably interface with heavier bus loads, such as multiple TTL inputs or long PCB traces, without signal degradation. All other electrical and timing parameters remain identical between the two versions.
Can SN74ALS638A-1DWR be used interchangeably with SN74ALS639A-1DWR on the same PCB?
No - while SN74ALS638A-1DWR and SN74ALS639A-1DWR share identical pinout, package, supply, and timing specifications, they differ fundamentally in logic function: SN74ALS638A-1DWR is inverting, and SN74ALS639A-1DWR is true (non-inverting). Swapping them without adjusting upstream/downstream logic will invert critical control or data signals. The SN74ALS638A-1DWR must be used only where inverting behavior is explicitly required by the system design.
What are the absolute maximum voltage ratings for the A-bus and B-bus pins of SN74ALS638A-1DWR?
The A-bus I/O pins (A1–A8) of SN74ALS638A-1DWR tolerate up to 7 V, consistent with open-collector TTL compatibility and pull-up flexibility. The B-bus I/O pins (B1–B8) are limited to 5.5 V maximum, reflecting their 3-state CMOS/TTL output structure. Exceeding either rating risks permanent damage. VCC must not exceed 7 V, and input voltages at DIR or OE must also stay within 0–7 V.
Does SN74ALS638A-1DWR support hot-swap or live-insertion into a powered backplane?
No - SN74ALS638A-1DWR lacks explicit hot-swap protection features such as power-up sequencing control, Ioff (power-off protection), or bus-fault current limiting. Its absolute maximum ratings do not cover dynamic insertion stress, and uncontrolled voltage sequencing during insertion may violate VI or VCC limits. For hot-swap applications, dedicated hot-swap controllers or buffers with Ioff and power sequencing must be used alongside the SN74ALS638A-1DWR.
How does the direction-control (DIR) and output-enable (OE) logic interact in SN74ALS638A-1DWR?
In SN74ALS638A-1DWR, OE is dominant: when OE is high (disabled), both A and B outputs enter high-impedance states regardless of DIR state. When OE is low (enabled), DIR determines data flow direction - DIR low enables B→A transfer, and DIR high enables A→B transfer. This hierarchical control allows system-level isolation (via OE) followed by fine-grained directional routing (via DIR), supporting flexible bus arbitration schemes in multi-master environments.
SN74ALS638A-1DWR 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, 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-1DWR FAQ
1.How can I place an order for SN74ALS638A-1DWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS638A-1DWR 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-1DWR reliable?
The price and inventory of SN74ALS638A-1DWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS638A-1DWR is usually 5 days.
3.What payment methods are accepted for SN74ALS638A-1DWR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS638A-1DWR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS638A-1DWR?
SN74ALS638A-1DWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS638A-1DWR 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-1DWR?
For technical support, including SN74ALS638A-1DWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS638A-1DWR requirements.
6.How does Aetrix verify that SN74ALS638A-1DWR is sourced from the original manufacturer or authorized distributors?
All SN74ALS638A-1DWR 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-1DWR meets industry standards.
7.What is the process for return or replacement of SN74ALS638A-1DWR?
All SN74ALS638A-1DWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS638A-1DWR, 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-1DWR part is unused and in its original packaging.
Return procedure for SN74ALS638A-1DWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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