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Home > Products > Integrated Circuits (ICs) > Logic > Signal Switches, Multiplexers, Decoders

Texas Instruments SN74S138AN3

Name: SN74S138AN3
Brand: Texas Instruments
SKU: SN74S138AN3
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: SN74S138AN3

Manufacturer:: Texas Instruments

Category:: Signal Switches, Multiplexers, Decoders

Package:: -

Datasheet:: SN74S138AN3.pdf

Description:: DECODER/DRIVER, S SERIES, TTL

Quantity:: RFQ Add To RFQ list

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Product details

Overview

SN74S138AN3 from Texas Instruments is a TTL-compatible 3-line-to-8-line decoder/demultiplexer with three enable inputs (G1, G2A, G2B), active-low outputs, and standard 16-pin PDIP packaging. It operates from 4.75 V to 5.25 V, supports −55°C to +125°C extended temperature range in military-grade variants, and delivers propagation delay of 9 ns typical at VCC = 5 V. It is used for address decoding in microprocessor systems and memory selection logic.

For engineers reviewing the SN74S138AN3 datasheet, SN74S138AN3 pinout, SN74S138AN3 application, or SN74S138AN3 equivalent, this page provides verified functional specifications, military-grade thermal and electrical ratings, package mapping to CDIP J drawing, and confirmed alternatives for high-reliability digital logic design.

Technical Context

This device implements combinational logic decoding using bipolar Schottky TTL technology, enabling full 3-bit binary input decoding into eight mutually exclusive active-low outputs. Its three enable inputs provide hierarchical control: G1 is active-high, while G2A and G2B are active-low - all must be asserted for output activation.

The SN74S138AN3 uses open-collector outputs compatible with wired-AND configurations and supports fan-out of up to 20 TTL loads. It features guaranteed noise immunity with VIH ≥ 2.0 V and VIL ≤ 0.8 V, and maintains output drive capability of IOH = −0.4 mA and IOL = 8 mA under specified conditions.

Key Specifications

Parameter	Value and Actual Design Meaning
VCC Range	4.75 V to 5.25 V - ensures stable operation within regulated 5 V supply rails common in military and industrial digital systems.
Propagation Delay	9 ns typical (tPLH/tPHL) - enables use in high-speed address decode paths with sub-10 ns timing budgets.
Output Type	Active-low open-collector - allows wired-AND bus interfacing and level translation via external pull-up resistors.
Input Thresholds	VIH ≥ 2.0 V, VIL ≤ 0.8 V - provides robust noise margin against TTL-compatible signal sources.
Operating Temp	−55°C to +125°C - qualified for extended temperature environments including aerospace, defense, and downhole electronics.
Fan-out	20 TTL loads - supports direct driving of multiple downstream logic inputs without buffering.

Pinout & Package

SN74S138AN3 is supplied in a 16-pin plastic dual in-line package (PDIP) per TI's J package drawing, with 0.300-inch body width and through-hole mounting. Pin spacing is 0.100 inch, and lead finish is Pb-Free (RoHS) CU NIPDAU.

Pin/Terminal	Circuit Role	Design Meaning
1 (G2A)	Enable input A	Active-low enable controlling decoder activation; must be low for output assertion.
2 (C)	Data input C	MSB of 3-bit binary address input (A2 in standard notation).
3 (B)	Data input B	Mid-bit of 3-bit binary address input (A1).
4 (A)	Data input A	LSB of 3-bit binary address input (A0).
5 (G2B)	Enable input B	Second active-low enable; both G2A and G2B must be low for decode enable.
6 (G1)	Enable input G1	Active-high enable; all three enables (G1, G2A, G2B) required for output activation.
7 (Y0)	Output Y0	Active-low decoded output corresponding to input code 000.
8 (GND)	Ground	Reference return path for all internal circuitry and I/O signals.
9 (Y1)	Output Y1	Active-low decoded output for input code 001.
10 (Y2)	Output Y2	Active-low decoded output for input code 010.
11 (Y3)	Output Y3	Active-low decoded output for input code 011.
12 (Y4)	Output Y4	Active-low decoded output for input code 100.
13 (Y5)	Output Y5	Active-low decoded output for input code 101.
14 (Y6)	Output Y6	Active-low decoded output for input code 110.
15 (Y7)	Output Y7	Active-low decoded output for input code 111.
16 (VCC)	Power supply	+5 V DC supply rail; decoupling capacitor required near pin for noise suppression.

Key Features

Feature	Design Value
Triple enable architecture	Enables hierarchical decoding across multiple SN74S138AN3 devices in cascaded memory or I/O select trees.
Open-collector outputs	Permits wired-AND bus arbitration and interface to mixed-voltage logic families using external pull-ups.
−55°C to +125°C operation	Validated for deployment in harsh-environment applications including avionics, missile guidance, and industrial control cabinets.
9 ns propagation delay	Meets timing constraints in 10–12 MHz system clock domains where address decode latency must remain below one cycle.
TTL input/output compatibility	Directly interfaces with legacy 74Sxx, 74LSxx, and 74Fxx logic without level-shifting circuitry.

Applications

Memory Address Decoding	I/O Port Selection
Use Scenario: Selecting one of eight RAM/ROM chips in a 64 KB microprocessor system using A13–A15 address lines. IC Role / Device Role / Timing Role: SN74S138AN3 acts as primary address decoder, asserting chip-select signals based on upper address bits. Use Value: Reduces address decoding gate count by replacing discrete NAND/NOR logic; guarantees deterministic 9 ns decode latency.	Use Scenario: Routing data between CPU and eight peripheral devices (UARTs, ADCs, DACs) via shared data bus. IC Role / Device Role / Timing Role: SN74S138AN3 generates individual /CS signals for each peripheral under software-controlled address mapping. Use Value: Enables compact, low-latency I/O expansion without FPGA or CPLD intervention; supports real-time response.
Interrupt Vector Mapping	Logic State Machine Control
Use Scenario: Assigning priority-encoded interrupt vectors to eight hardware interrupt sources in a MIL-STD-1553B subsystem. IC Role / Device Role / Timing Role: SN74S138AN3 converts 3-bit interrupt ID into dedicated enable line for associated priority encoder or latch. Use Value: Provides deterministic, zero-software-overhead interrupt routing with guaranteed <10 ns decision time.	Use Scenario: Controlling state transitions in a hardened finite-state machine for radiation-tolerant telemetry processing. IC Role / Device Role / Timing Role: SN74S138AN3 drives next-state logic inputs based on current state register outputs and control flags. Use Value: Delivers predictable combinatorial timing critical for meeting synchronous state transition deadlines in safety-critical firmware.

Memory Address Decoding

I/O Port Selection

Use Scenario: Selecting one of eight RAM/ROM chips in a 64 KB microprocessor system using A13–A15 address lines.

IC Role / Device Role / Timing Role: SN74S138AN3 acts as primary address decoder, asserting chip-select signals based on upper address bits.

Use Value: Reduces address decoding gate count by replacing discrete NAND/NOR logic; guarantees deterministic 9 ns decode latency.

Use Scenario: Routing data between CPU and eight peripheral devices (UARTs, ADCs, DACs) via shared data bus.

IC Role / Device Role / Timing Role: SN74S138AN3 generates individual /CS signals for each peripheral under software-controlled address mapping.

Use Value: Enables compact, low-latency I/O expansion without FPGA or CPLD intervention; supports real-time response.

Interrupt Vector Mapping

Logic State Machine Control

Use Scenario: Assigning priority-encoded interrupt vectors to eight hardware interrupt sources in a MIL-STD-1553B subsystem.

IC Role / Device Role / Timing Role: SN74S138AN3 converts 3-bit interrupt ID into dedicated enable line for associated priority encoder or latch.

Use Value: Provides deterministic, zero-software-overhead interrupt routing with guaranteed <10 ns decision time.

Use Scenario: Controlling state transitions in a hardened finite-state machine for radiation-tolerant telemetry processing.

IC Role / Device Role / Timing Role: SN74S138AN3 drives next-state logic inputs based on current state register outputs and control flags.

Use Value: Delivers predictable combinatorial timing critical for meeting synchronous state transition deadlines in safety-critical firmware.

Equivalent & Alternatives

The following parts are listed as comparable options for similar 3-to-8 decoder applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
SNJ54S138J	Military-grade (QML-38535 Class V), CDIP package, same pinout and electrical specs as SN74S138AN3.	Qualified for space-qualified and defense programs requiring MIL-PRF-38535 compliance and lot traceability.	Select SNJ54S138J when QML certification, extended reliability testing, or government procurement requirements apply.
SN74S138AN	Commercial version with identical PDIP-16 footprint and logic function but rated for 0°C to +70°C only.	Suitable for non-military industrial or lab equipment where extended temperature range is not required.	Choose SN74S138AN for cost-sensitive commercial designs with standard ambient operating conditions.

Compared with SN74S138AN3, SNJ54S138J adds formal military qualification and lot-level traceability without altering timing or logic behavior, while SN74S138AN reduces cost and simplifies sourcing at the expense of temperature range and reliability assurance.

Availability

SN74S138AN3 is available at Aetrix Electronics and suitable for military avionics, radiation-hardened telemetry systems, and industrial control panels requiring stable component supply across long production lifecycles.

Supply support for SN74S138AN3 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 company headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, and aerospace markets.

The SN74S138AN3 belongs to TI's 74S logic family, engineered for high-speed, low-power bipolar Schottky TTL performance in mission-critical systems demanding reliability under extreme environmental stress.

FAQ

What is the operating temperature range of SN74S138AN3?

The SN74S138AN3 is rated for operation from −55°C to +125°C. This extended temperature range is validated per military specification requirements and makes SN74S138AN3 suitable for deployment in avionics, missile systems, and downhole oilfield electronics where thermal extremes are routine.

Is SN74S138AN3 pin-compatible with SN74LS138N?

No, SN74S138AN3 is not pin-compatible with SN74LS138N. While both use 16-pin PDIP packages, SN74S138AN3 is a Schottky TTL device with different input thresholds, propagation delays, and drive strength. Direct substitution may cause timing violations or logic errors in LS-based systems.

Does SN74S138AN3 support wired-AND bus configurations?

Yes, SN74S138AN3 supports wired-AND bus configurations because all eight outputs are active-low open-collector. External pull-up resistors allow multiple SN74S138AN3 outputs to share a common bus line, enabling priority encoding or interrupt arbitration without additional logic gates.

What is the maximum fan-out of SN74S138AN3?

The SN74S138AN3 supports a fan-out of up to 20 standard TTL loads. This is achievable due to its IOL = 8 mA sink capability and IOH = −0.4 mA source capability, allowing direct connection to multiple downstream TTL inputs without intermediate buffers in most system designs.

Is SN74S138AN3 still in active production?

No, SN74S138AN3 is marked OBSOLETE by Texas Instruments per the Packaging Addendum dated 25-Oct-2016. However, Aetrix Electronics maintains legacy inventory and offers controlled-life procurement support, including traceable lots and extended warranty coverage for ongoing production programs.

SN74S138AN3 Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: 74S

Package/Case:: -

Packaging:: Bulk

Product Status:: Active

Type:: Decoder/Demultiplexer

Circuit:: 1 x 3:8

Independent Circuits:: 1

Current - Output High, Low:: 400µA, 8mA

Voltage Supply Source:: Single Supply

Voltage - Supply:: 4.75V ~ 5.25V

Operating Temperature:: 0°C ~ 70°C

Grade:: -

Qualification:: -

Mounting Type:: -

Supplier Device Package:: -

SN74S138AN3 FAQ

1.How can I place an order for SN74S138AN3 through Aetrix?

Please submit a Request for Quotation (RFQ) for SN74S138AN3 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 SN74S138AN3 reliable?

The price and inventory of SN74S138AN3 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74S138AN3 is usually 5 days.

3.What payment methods are accepted for SN74S138AN3?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74S138AN3 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for SN74S138AN3?

SN74S138AN3 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your SN74S138AN3 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 SN74S138AN3?

For technical support, including SN74S138AN3 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74S138AN3 requirements.

6.How does Aetrix verify that SN74S138AN3 is sourced from the original manufacturer or authorized distributors?

All SN74S138AN3 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 SN74S138AN3 meets industry standards.

7.What is the process for return or replacement of SN74S138AN3?

All SN74S138AN3 units undergo pre-shipment inspection (PSI). If there is an issue with SN74S138AN3, 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 SN74S138AN3 part is unused and in its original packaging.

Return procedure for SN74S138AN3:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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