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Texas Instruments SN74ALS638A-1DWRG4
- Part No.:
- SN74ALS638A-1DWRG4
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS638A-1DWRG4.pdf
- Description:
- IC TXRX INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
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Product details
Overview
SN74ALS638A-1DWRG4 from Texas Instruments is an octal bus transceiver with inverting logic, open-collector A-bus outputs and 3-state B-bus outputs, rated for 0°C to 70°C operation, supporting bidirectional data flow between mixed-logic buses with 48 mA max IOL (A/B ports), used in legacy industrial backplane and TTL-level bus interface systems.
For engineers reviewing the SN74ALS638A-1DWRG4 datasheet, SN74ALS638A-1DWRG4 pinout, SN74ALS638A-1DWRG4 application, or SN74ALS638A-1DWRG4 equivalent, key selection criteria include its -1 version's enhanced 48 mA sink capability, DW package compatibility with SOIC-20 footprints, direction-control (DIR) and output-enable (OE) logic timing, and open-collector/3-state bus isolation behavior.
Technical Context
This device implements asynchronous bidirectional bus translation using separate DIR and OE control inputs: DIR selects data direction (A→B or B→A), while OE enables/disables both bus sides simultaneously. The A-bus outputs are open-collector, requiring external pull-ups; B-bus outputs are active-high 3-state, compatible with standard TTL loads.
It operates within 4.5 V–5.5 V VCC, supports 0°C–70°C ambient, and features propagation delays as low as 2 ns (A→B) and 5 ns (OE→B enable), with VOL ≤ 0.5 V at IOL = 48 mA and VOH ≥ 2.4 V at IOH = –15 mA on B ports - all specified under defined load conditions (CL = 50 pF, RL = 680 Ω for A, R1/R2 = 500 Ω for B).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - ensures compatibility with standard 5 V TTL and ALS logic supply rails. |
| IOL (max) | 48 mA - confirmed only for SN74ALS638A-1 variant; enables direct driving of higher-current loads without external buffers. |
| tPLH / tPHL (A→B) | 2 ns to 12 ns - defines minimum clock-to-output delay when transmitting from open-collector A bus to 3-state B bus. |
| VOL @ IOL=48 mA | ≤ 0.5 V - guarantees logic-low integrity at full sink current, critical for noise margin in noisy industrial environments. |
| VOH @ IOH=–15 mA | ≥ 2.4 V - ensures reliable high-level signaling into TTL-compatible inputs under worst-case loading. |
| Operating Temp | 0°C to 70°C - specifies commercial-grade thermal envelope suitable for non-automotive embedded control applications. |
| Logic Function | Inverting - output polarity on B bus is inverted relative to A bus input, per function table and device marking. |
Pinout & Package
SN74ALS638A-1DWRG4 is housed in a 20-pin SOIC (DW) package, 7.5 mm wide, 12.83 mm long, 2.65 mm max height, RoHS-compliant with NIPDAU lead finish and Level-1 MSL rating.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | Low = B→A data transfer; High = A→B data transfer; TTL-compatible threshold (VIL ≤ 0.8 V, VIH ≥ 2 V). |
| 2 (A1) | A-Bus Input/Output | Open-collector I/O port; requires external pull-up; sinks up to 48 mA when active low. |
| 3–9 (A2–A8) | A-Bus Input/Output | Seven additional open-collector A-bus ports, identical in function and rating to A1. |
| 10 (GND) | Ground Reference | Primary power return path; must be low-impedance for stable noise margin and switching performance. |
| 11–18 (B1–B8) | B-Bus Output | Eight 3-state outputs; driven high/low when enabled; high-impedance when OE = high. |
| 19 (OE) | Output Enable Input | Active-low control: Low = outputs enabled; High = all B outputs high-Z, A outputs pulled high via external resistors. |
| 20 (VCC) | Power Supply | +5 V nominal supply; absolute max 7 V; decoupling capacitor required near pin for transient current handling. |
Key Features
| Feature | Design Value |
|---|---|
| Inverting Logic Path | Ensures signal inversion across A→B transmission, enabling compatibility with legacy inverted bus protocols and level-shifting schemes. |
| 48 mA Sink Capability (-1 version) | Supports direct connection to higher-current loads (e.g., LEDs, relays, or multiple TTL inputs) without external drivers. |
| Asynchronous Bidirectional Control | Independent DIR and OE pins allow dynamic bus direction switching and complete isolation - no clock or synchronization required. |
| Mixed-Interface Bus Bridging | Native support for interfacing open-collector (A) and 3-state (B) buses eliminates need for discrete level-shifting or buffering components. |
| SOIC-20 Package with Standard Footprint | Enables drop-in replacement in space-constrained PCB layouts designed for industry-standard 20-pin SOIC footprints (JEDEC MS-013). |
Applications
| Industrial Backplane Interface | Legacy TTL System Expansion |
|---|---|
|
Use Scenario: Interfacing microcontroller address/data buses to legacy parallel backplanes with open-collector arbitration lines. IC Role / Device Role / Timing Role: SN74ALS638A-1DWRG4 acts as bidirectional bus translator, isolating CPU-side 3-state signals from shared open-collector bus segments during arbitration. Use Value: Enables deterministic bus sharing using DIR-controlled direction and OE-based isolation, reducing contention risk in multi-master systems. |
Use Scenario: Adding peripheral modules (e.g., EPROM, I/O expanders) to vintage 8-bit computer systems using TTL-level signaling. IC Role / Device Role / Timing Role: SN74ALS638A-1DWRG4 serves as inverting transceiver between CPU data bus and peripheral data bus, matching voltage/current requirements of 74LS/ALS families. Use Value: Provides 48 mA sink drive for peripherals requiring stronger low-side current, improving signal integrity over long traces in retro-computing designs. |
| Test Equipment Signal Routing | Programmable Logic Interface |
|
Use Scenario: Configurable signal routing in automated test equipment where DUT interfaces require selectable bus direction and isolation. IC Role / Device Role / Timing Role: SN74ALS638A-1DWRG4 functions as controllable bus coupler, with DIR selecting stimulus/response path and OE enabling safe hot-swap isolation. Use Value: Eliminates need for mechanical switches or relays; supports software-defined signal paths with sub-12 ns propagation delay and guaranteed VOL at full load. |
Use Scenario: Connecting GAL/PAL outputs to external bus structures requiring open-collector wired-AND or 3-state multiplexing. IC Role / Device Role / Timing Role: SN74ALS638A-1DWRG4 bridges programmable logic device outputs to system buses, translating PAL active-low outputs to open-collector A-bus or 3-state B-bus formats. Use Value: Preserves logic inversion inherent in many PAL architectures while providing robust drive strength and bus isolation via OE control. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS638AN | Dual-in-line (N) package, 20-pin PDIP; same electrical specs but no -1 version IOL enhancement (rated 24 mA max). | Suitable for through-hole prototyping or legacy board rework where SOIC footprint is unavailable. | Select SN74ALS638AN only when manual assembly or socket-based testing is required; not recommended for new SOIC-based designs. |
| SN74AS638A | Faster propagation (2–7 ns A→B), higher IOL (64 mA), but increased ICC (up to 122 mA) and tighter VIH/VIL thresholds. | Better suited for high-speed synchronous bus systems where timing budget is constrained and power dissipation is acceptable. | Choose SN74AS638A only if speed >12 ns A→B delay is unacceptable and system can accommodate higher supply current and stricter input levels. |
Compared with SN74ALS638AN and SN74AS638A, SN74ALS638A-1DWRG4 uniquely balances enhanced 48 mA drive, SOIC packaging, and ALS-family power efficiency - making it optimal for cost-sensitive, space-constrained industrial upgrades requiring proven reliability without speed or power penalties.
Availability
SN74ALS638A-1DWRG4 is available at Aetrix Electronics and suitable for industrial backplane interface, legacy TTL system expansion, and test equipment signal routing requiring stable component supply, long-lifecycle support, and RoHS-compliant sourcing.
Supply support for SN74ALS638A-1DWRG4 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 specializing in analog, embedded processing, and logic solutions, with decades of heritage in TTL, ALS, and AS logic families.
SN74ALS638A-1DWRG4 belongs to TI's legacy 74ALS logic product line, engineered for robust, low-power, medium-speed bus interfacing in industrial and instrumentation applications where reliability and backward compatibility are critical.
FAQ
What is the key functional difference between SN74ALS638A-1DWRG4 and the standard SN74ALS638A?
The SN74ALS638A-1DWRG4 is the enhanced "-1" version of the SN74ALS638A, with a confirmed maximum low-level output current (IOL) rating of 48 mA - double the 24 mA limit of the standard version. This applies only when VCC is maintained between 4.75 V and 5.25 V, and directly impacts drive capability for open-collector A-bus loads. All other electrical and timing specifications remain identical to the base SN74ALS638A.
Does SN74ALS638A-1DWRG4 support true bidirectional data flow without external logic?
Yes. SN74ALS638A-1DWRG4 natively supports bidirectional data flow using two dedicated control inputs: DIR selects direction (A→B or B→A), and OE enables or disables both bus sides simultaneously. No external gates or timing circuitry are needed - the device handles asynchronous handshaking entirely internally, as verified by its function table and logic diagram.
Can SN74ALS638A-1DWRG4 be used with 3.3 V logic systems?
No. SN74ALS638A-1DWRG4 is strictly a 5 V device: its recommended VCC range is 4.5 V–5.5 V, and its input thresholds (VIH ≥ 2 V, VIL ≤ 0.8 V) and output drive characteristics are optimized for TTL/ALS-level signaling. Direct connection to 3.3 V systems risks violating absolute maximum ratings and invalidating logic thresholds; level-shifting circuitry is required for interoperability.
What is the significance of the "DWRG4" suffix in SN74ALS638A-1DWRG4?
The "DWRG4" suffix identifies the specific packaging and compliance variant: "DW" = SOIC-20 package, "R" = tape-and-reel packaging (though this part uses tube per TI documentation), "G4" = RoHS-compliant, lead-free (NIPDAU) finish. TI's official packaging addendum confirms SN74ALS638A-1DWRG4 is a RoHS-compliant SOIC-20 variant with Level-1 MSL rating and 0°C–70°C temperature grade.
How does the open-collector A-bus interface with standard pull-up resistors?
The A-bus outputs of SN74ALS638A-1DWRG4 are open-collector and require external pull-up resistors to VCC (or another logic rail). Typical values range from 1.8 kΩ to 10 kΩ depending on bus capacitance and speed requirements. With IOL = 48 mA and VOL ≤ 0.5 V, a 2.2 kΩ pull-up yields ~5 V – (48 mA × 2.2 kΩ) ≈ –100 V - confirming that practical resistor values ensure valid high-level voltage while maintaining fast rise times and noise immunity.
SN74ALS638A-1DWRG4 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-1DWRG4 FAQ
1.How can I place an order for SN74ALS638A-1DWRG4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS638A-1DWRG4 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-1DWRG4 reliable?
The price and inventory of SN74ALS638A-1DWRG4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS638A-1DWRG4 is usually 5 days.
3.What payment methods are accepted for SN74ALS638A-1DWRG4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS638A-1DWRG4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS638A-1DWRG4?
SN74ALS638A-1DWRG4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS638A-1DWRG4 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-1DWRG4?
For technical support, including SN74ALS638A-1DWRG4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS638A-1DWRG4 requirements.
6.How does Aetrix verify that SN74ALS638A-1DWRG4 is sourced from the original manufacturer or authorized distributors?
All SN74ALS638A-1DWRG4 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-1DWRG4 meets industry standards.
7.What is the process for return or replacement of SN74ALS638A-1DWRG4?
All SN74ALS638A-1DWRG4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS638A-1DWRG4, 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-1DWRG4 part is unused and in its original packaging.
Return procedure for SN74ALS638A-1DWRG4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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