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Texas Instruments SN74ALS638AN
- Part No.:
- SN74ALS638AN
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74ALS638AN.pdf
- Description:
- IC TRANSCEIVER INVERT 5.5V 20DIP
- Quantity:
- Payment:
- Shipping:
Inventory:1,646
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Product details
Overview
SN74ALS638AN from Texas Instruments is an octal bus transceiver with inverting logic, open-collector A-bus outputs, and 3-state B-bus outputs, operating at 4.5–5.5 V supply voltage with 0°C to 70°C temperature range. It enables bidirectional data flow between open-collector and 3-state buses in legacy industrial control backplanes and TTL-compatible memory expansion systems.
For engineers reviewing the SN74ALS638AN datasheet, SN74ALS638AN pinout, SN74ALS638AN application, or SN74ALS638AN equivalent, key selection criteria include direction-control (DIR) and output-enable (OE) timing behavior, A-bus sink current capability (24 mA standard / 48 mA -1 version), B-bus VOL under 15 mA load, and compatibility with 300-mil PDIP layout constraints.
Technical Context
This device implements asynchronous bidirectional bus translation using dual-output architecture: A-side ports are open-collector with VIH/VIL thresholds of 2 V/0.8 V and support up to 48 mA sink per pin (SN74ALS638A-1 variant); B-side ports are 3-state with VOH ≥ 2.4 V at –15 mA and VOL ≤ 0.5 V at 24 mA.
Propagation delays are asymmetric: A→B paths exhibit 2–12 ns tPLH/tPHL, while B→A paths range 8–30 ns; OE-to-B enable/disable times (tPZH/tPZL) are 5–25 ns, confirming suitability for burst-mode bus arbitration in non-synchronous systems.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Function | Inverting octal bus transceiver with DIR/OE control |
| Supply Voltage | 4.5–5.5 V - compatible with standard TTL power rails |
| A-Bus Output Type | Open-collector - supports wired-AND, level shifting, and pull-up resistor interfacing |
| B-Bus Output Type | 3-state - enables multiplexed bus sharing without contention |
| Max Sink Current (A port) | 24 mA (standard), 48 mA (–1 version) - drives standard TTL loads directly |
| Propagation Delay (A→B) | 2–12 ns - ensures fast local bus handshaking in backplane designs |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade industrial equipment |
Pinout & Package
SN74ALS638AN uses a 20-pin plastic DIP (N package), 300-mil width, with 0.1-inch lead pitch. Pin 1 is marked by notch or dot; package height is 4.95 mm max.
| 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 | Power return path for all internal logic and I/O stages |
| 11–18 (B1–B8) | B-Bus I/O Terminals | 3-state outputs; high-impedance when OE = HIGH |
| 19 (OE) | Output Enable Input | Low = outputs active; High = all outputs disabled (A open, B high-Z) |
| 20 (VCC) | Positive Supply | Connects to +5 V rail; decoupling capacitor required near pin |
Key Features
| Feature | Design Value |
|---|---|
| Inverting Logic Path | Ensures signal polarity consistency across A↔B translation in legacy TTL bus architectures |
| Asymmetric Propagation Delay | A→B delay (2–12 ns) is faster than B→A (8–30 ns), optimizing master-slave read/write timing asymmetry |
| Open-Collector A Outputs | Enables wired-AND bus arbitration and direct interface to higher-voltage or mixed-logic systems via pull-up |
| 3-State B Outputs | Allows multiple SN74ALS638AN devices to share a common B-bus without hardware contention |
| –1 Version IOL Rating | 48 mA sink capability on A ports supports driving heavier capacitive loads or multiple TTL inputs |
Applications
| Industrial Backplane Bus Interface | Legacy Memory Expansion Module |
|---|---|
|
Use Scenario: Interfacing microprocessor address/data buses to isolated peripheral slots in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional bus translator isolating CPU bus from field I/O modules using DIR-controlled data flow and OE-gated isolation during slot reset. Use Value: Prevents bus contention during hot-swap events and supports TTL-level signal integrity over 15 cm backplane traces. |
Use Scenario: Adding external RAM/ROM to 8-bit microcontrollers with limited address space, requiring shared data bus access. IC Role / Device Role / Timing Role: Direction-controlled transceiver enabling CPU read/write cycles to external memory banks via time-multiplexed A/B bus segments. Use Value: Eliminates need for discrete bus buffers and simplifies PCB routing with single-chip 8-bit bidirectional interface. |
| Test Equipment Signal Routing | Automated Test Fixture Control |
|
Use Scenario: Routing digital stimulus signals between pattern generator and DUT in boundary-scan test systems. IC Role / Device Role / Timing Role: Isolating test controller outputs from DUT inputs using OE-driven high-Z state during measurement phases. Use Value: Guarantees signal integrity during high-speed vector capture by eliminating back-driving during sampling windows. |
Use Scenario: Controlling relay matrices and sensor interfaces in production-line functional testers with shared control bus. IC Role / Device Role / Timing Role: Enabling centralized command distribution from test host to multiple fixture zones via open-collector A-bus wiring. Use Value: Supports daisy-chained fault signaling and reduces cabling complexity through wired-AND status reporting. |
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 | True (non-inverting) logic function; identical pinout, package, and electrical specs except polarity | Required where signal inversion would break existing bus protocol handshake sequences | Select SN74ALS639AN only when system-level timing analysis confirms inverting logic introduces setup/hold violations |
| SN74AS638AN | Faster propagation (A→B: 2–7 ns vs. 2–12 ns); higher IOL (64 mA vs. 24 mA); same pinout and logic function | Suitable for high-speed backplanes (>20 MHz clock domains) but increases power consumption (ICC up to 122 mA) | Choose SN74AS638AN only if measured tPHL/tPLH margins fall below 3 ns in target layout; verify thermal derating at full load |
Compared with SN74ALS638AN, SN74ALS639AN provides identical timing and drive strength with true logic-critical for protocol-compliant bus extensions-while SN74AS638AN delivers 40% lower propagation delay at the cost of doubled ICC and stricter layout decoupling requirements.
Availability
SN74ALS638AN is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy memory expansion modules, and automated test fixture control requiring stable component supply across long-lifecycle embedded programs.
Supply support for SN74ALS638AN 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.
SN74ALS638AN belongs to the 74ALS family of advanced low-power Schottky logic devices, designed specifically for reliable, noise-immune bus interfacing in commercial-temperature industrial control systems.
FAQ
What is the maximum sink current rating for SN74ALS638AN A-port outputs?
The standard SN74ALS638AN supports 24 mA per A-port output under recommended conditions (VCC = 4.5–5.5 V, TA = 0°C to 70°C). A variant labeled SN74ALS638A-1 increases this to 48 mA when VCC is maintained between 4.75 V and 5.25 V. The SN74ALS638AN part number refers to the standard 24 mA version in PDIP packaging.
Does SN74ALS638AN support level translation between 5 V and 3.3 V buses?
No. SN74ALS638AN is a 5 V-only device with VIH = 2 V and VIL = 0.8 V, and its B-port outputs are rated for VOH ≥ 2.4 V at –15 mA-not compatible with 3.3 V logic thresholds. A-port open-collector operation allows external pull-up to 3.3 V, but B-port 3-state outputs cannot safely drive or be driven by 3.3 V systems without additional level-shifting circuitry.
Can SN74ALS638AN be used in place of SN74ALS639AN?
Only with circuit-level redesign. SN74ALS638AN implements inverting logic while SN74ALS639AN is true (non-inverting); swapping them without inverting upstream/downstream signals will reverse data polarity and corrupt communication. Both share identical pinout, timing, and drive strength-making them electrically interchangeable only when logic inversion is explicitly accommodated.
What is the purpose of the DIR and OE pins on SN74ALS638AN?
DIR (pin 1) controls data direction: DIR = LOW enables B→A transfer; DIR = HIGH enables A→B transfer. OE (pin 19) globally disables outputs: OE = HIGH places all A-ports in open-collector high-impedance and all B-ports in 3-state high-Z, isolating both buses. These two controls allow precise bus arbitration in multi-master systems using SN74ALS638AN.
Is SN74ALS638AN RoHS compliant?
Yes. SN74ALS638AN carries RoHS "Yes" certification per TI's Packaging Information Addendum, with NIPDAU lead finish and compliance verified for lead-free reflow processes. The device meets EU Directive 2011/65/EU requirements and contains no restricted substances above threshold limits.
SN74ALS638AN 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, 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
SN74ALS638AN FAQ
1.How can I place an order for SN74ALS638AN through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS638AN 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 SN74ALS638AN reliable?
The price and inventory of SN74ALS638AN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS638AN is usually 5 days.
3.What payment methods are accepted for SN74ALS638AN?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS638AN transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS638AN?
SN74ALS638AN orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS638AN 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 SN74ALS638AN?
For technical support, including SN74ALS638AN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS638AN requirements.
6.How does Aetrix verify that SN74ALS638AN is sourced from the original manufacturer or authorized distributors?
All SN74ALS638AN 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 SN74ALS638AN meets industry standards.
7.What is the process for return or replacement of SN74ALS638AN?
All SN74ALS638AN units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS638AN, 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 SN74ALS638AN part is unused and in its original packaging.
Return procedure for SN74ALS638AN:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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