My Inquiry
My Account
Texas Instruments SN74S138ANG4
- Part No.:
- SN74S138ANG4
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74S138ANG4.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16DIP
- Quantity:
- Payment:
- Shipping:
Inventory:1,461
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
SN74S138ANG4 from Texas Instruments is a high-speed TTL 3-to-8 line decoder/demultiplexer in a 16-pin PDIP package, featuring active-low outputs, three enable inputs (G1, G2A, G2B), propagation delay of 9.5 ns (typical at VCC = 5 V), and operating temperature range of 0°C to 70°C. It is used in address decoding for microprocessor systems and data routing in digital logic circuits.
For engineers reviewing the SN74S138ANG4 datasheet, SN74S138ANG4 pinout, SN74S138ANG4 application, or SN74S138ANG4 equivalent, this page delivers verified technical context, exact pin functions, real-world use cases in embedded control and memory addressing, and validated alternative options with documented functional and application-level differences.
Technical Context
The SN74S138ANG4 implements combinational logic decoding using Schottky-clamped bipolar transistor technology, enabling fast switching with guaranteed fan-out of 20 TTL loads. Its three enable inputs provide hierarchical expansion capability-G1 is active-high while G2A and G2B are active-low-allowing cascading of multiple devices without external gating logic.
It decodes three binary-weighted address inputs (A0, A1, A2) into eight mutually exclusive active-low outputs (Y0–Y7), with output states fully defined only when all enables are asserted. The device exhibits no internal latching or clocking behavior and operates strictly asynchronously.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74S (Schottky TTL), compatible with standard TTL input thresholds and drive levels |
| Propagation Delay | 9.5 ns typical (max 15 ns), enabling reliable operation in 33-MHz address decode paths |
| Supply Voltage | 4.75 V to 5.25 V-tight regulation required to maintain timing and noise margin |
| Output Drive | IOH = –1.0 mA / IOL = 20 mA-sufficient to directly drive multiple TTL inputs or small LED loads |
| Operating Temperature | 0°C to 70°C-commercial-grade rating suitable for industrial control panels and instrumentation |
| Enable Logic | G1 (active-high), G2A/G2B (active-low)-supports hierarchical decoding with inverted and non-inverted control signals |
Pinout & Package
SN74S138ANG4 is supplied in a 16-pin plastic dual in-line package (PDIP-N), 0.300-inch wide body, with 0.100-inch lead pitch and through-hole mounting compatibility.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (G2A) | Active-low enable input A | Must be low to activate decoder; used for chip select or hierarchical gating |
| 2 (G2B) | Active-low enable input B | Second active-low enable; both G2A and G2B must be low for function |
| 3 (G1) | Active-high enable input | Must be high to activate decoder; complements G2A/G2B for flexible control |
| 4 (C) | Address input (MSB) | Most significant bit of 3-bit address bus; determines Y4–Y7 vs Y0–Y3 group |
| 5 (B) | Address input (middle) | Mid-significance address bit; combines with A and C for full 3-bit decode |
| 6 (A) | Address input (LSB) | Least significant bit; final input determining unique output selection |
| 7 (GND) | Ground reference | Power return path; must be low-impedance for stable noise margins |
| 8 (Y7) | Active-low decoded output | Asserted only when A=1, B=1, C=1 and all enables active; drives downstream logic |
| 9 (Y6) | Active-low decoded output | Asserted only when A=0, B=1, C=1; one of eight mutually exclusive outputs |
| 10 (Y5) | Active-low decoded output | Asserted only when A=1, B=0, C=1; supports discrete peripheral selection |
| 11 (Y4) | Active-low decoded output | Asserted only when A=0, B=0, C=1; used in memory bank selection |
| 12 (Y3) | Active-low decoded output | Asserted only when A=1, B=1, C=0; enables I/O port mapping |
| 13 (Y2) | Active-low decoded output | Asserted only when A=0, B=1, C=0; supports interrupt vector decoding |
| 14 (Y1) | Active-low decoded output | Asserted only when A=1, B=0, C=0; used in status register addressing |
| 15 (Y0) | Active-low decoded output | Asserted only when A=0, B=0, C=0; default output for base address access |
| 16 (VCC) | Positive supply | +5 V DC power rail; requires local 0.1 µF ceramic bypass capacitor |
Key Features
| Feature | Design Value |
|---|---|
| High-speed decoding | 9.5 ns typical propagation delay enables use in 33-MHz bus systems without wait states |
| Three enable inputs | G1 (active-high), G2A/G2B (active-low) allow flexible hierarchical decoding across multiple ICs |
| Active-low outputs | Direct interface with common-base TTL inputs, open-collector drivers, and LED indicators |
| Standard pinout compatibility | Matches industry-standard 74xx138 footprint-enables drop-in replacement in legacy designs |
| Commercial temperature range | 0°C to 70°C operation certified per TI's production test flow for industrial control applications |
Applications
| Microprocessor Address Decoding | Memory Bank Selection |
|---|---|
Use Scenario: Selecting one of eight peripheral devices (UART, timer, GPIO) attached to an 8-bit microcontroller address bus. IC Role / Device Role / Timing Role: SN74S138ANG4 acts as a synchronous address decoder, asserting a single active-low chip-select line based on A0–A2 and enable conditions. Use Value: Eliminates need for discrete NAND gates; reduces PCB area and signal routing complexity by consolidating decode logic into one IC. | Use Scenario: Partitioning a 64 KB address space into eight 8 KB memory banks for SRAM or EPROM. IC Role / Device Role / Timing Role: SN74S138ANG4 generates bank-select signals synchronized to address strobes, ensuring glitch-free memory access. Use Value: Enables deterministic memory mapping with sub-10 ns setup/hold timing margins, critical for zero-wait-state operation. |
| I/O Port Expansion | Interrupt Vector Routing |
Use Scenario: Expanding parallel I/O capability using eight 8-bit latched ports controlled via shared data/address bus. IC Role / Device Role / Timing Role: SN74S138ANG4 selects individual port ICs (e.g., 74LS244/245) during write/read cycles using address and control lines. Use Value: Provides deterministic, low-latency port selection without software overhead-ideal for real-time control loops. | Use Scenario: Assigning priority-encoded interrupt vectors to eight different hardware sources in an embedded controller. IC Role / Device Role / Timing Role: SN74S138ANG4 routes interrupt request lines to dedicated vector lines (INT0–INT7) based on source ID. Use Value: Delivers fixed-latency interrupt acknowledgment (<15 ns max), supporting deterministic response in safety-critical systems. |
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 |
|---|---|---|---|
| SN74LS138N | Slower propagation delay (22 ns typ), lower drive (IOL = 8 mA), standard TTL (not Schottky) | Suitable for lower-speed systems (<10 MHz); higher power consumption at same frequency | Select when cost sensitivity outweighs speed requirement and existing LS-family design reuse is prioritized |
| SN74HC138N | CMOS technology, wider VCC range (2–6 V), lower Icc (8 µA), but slower at 5 V (21 ns typ) | Enables mixed-voltage system integration; unsuitable for direct TTL fan-out without level translation | Choose for battery-powered or low-power applications where 5-V TTL compatibility is not mandatory |
Compared with SN74LS138N and SN74HC138N, SN74S138ANG4 delivers the fastest propagation delay and highest output sink current in the 138 family, making it optimal for timing-critical address decode in legacy 5-V TTL systems where speed and drive strength are primary constraints.
Availability
SN74S138ANG4 is available at Aetrix Electronics and suitable for industrial control panels, legacy instrumentation interfaces, and military-grade repair programs requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74S138ANG4 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic ICs with broad industrial, automotive, and aerospace qualification programs.
The SN74S138ANG4 belongs to TI's legacy 74S logic family, designed specifically for high-speed digital systems requiring sub-10 ns propagation delays and robust TTL-compatible interfacing in commercial-temperature environments.
FAQ
What is the maximum clock frequency supported by SN74S138ANG4?
The SN74S138ANG4 is an asynchronous combinational logic device with no internal clock. Its usable frequency depends on system-level timing: with a 9.5 ns typical propagation delay, it supports clean address decode in bus systems up to approximately 33 MHz when paired with appropriate setup/hold margins. SN74S138ANG4 does not operate on a clock signal but responds immediately to input changes.
Can SN74S138ANG4 drive LEDs directly?
Yes, SN74S138ANG4 can drive LEDs directly via its active-low outputs. Each output sinks up to 20 mA (IOL), sufficient for standard 5-mm LEDs with a series resistor (e.g., 220 Ω at 5 V yields ~14 mA). Ensure VCC remains within 4.75–5.25 V and that total package power dissipation stays within limits under sustained load.
Is SN74S138ANG4 RoHS compliant?
No, SN74S138ANG4 is not RoHS compliant. It uses lead-based solder (SNPB finish) and is designated as "No" in TI's RoHS column. This part is intended for legacy repair, military/aerospace, or industrial applications where exemption from RoHS Directive 2011/65/EU applies.
How many SN74S138ANG4 devices can be cascaded for larger decoding?
Multiple SN74S138ANG4 devices can be cascaded using their enable inputs: one device's outputs (e.g., Y0–Y3) drive G2A/G2B of subordinate units, while G1 remains tied high. This allows expansion to 4-to-16, 5-to-32, or larger decoding trees. SN74S138ANG4's three enable pins are explicitly designed for this hierarchical configuration without external logic.
What is the pin 1 marking and orientation for SN74S138ANG4?
SN74S138ANG4 uses standard PDIP orientation: pin 1 is located at the left end of the top row, identified by a circular indentation or notch at the top-left corner of the package. The part marking "SN74S138AN" appears on the top surface, aligned left-to-right starting near pin 1. No additional suffix (e.g., G4) appears in the physical marking.
SN74S138ANG4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74S
- Package/Case:
- 16-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Discontinued at Digi-Key
- 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:
- Through Hole
- Supplier Device Package:
- 16-PDIP
SN74S138ANG4 FAQ
1.How can I place an order for SN74S138ANG4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74S138ANG4 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 SN74S138ANG4 reliable?
The price and inventory of SN74S138ANG4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74S138ANG4 is usually 5 days.
3.What payment methods are accepted for SN74S138ANG4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74S138ANG4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74S138ANG4?
SN74S138ANG4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74S138ANG4 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 SN74S138ANG4?
For technical support, including SN74S138ANG4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74S138ANG4 requirements.
6.How does Aetrix verify that SN74S138ANG4 is sourced from the original manufacturer or authorized distributors?
All SN74S138ANG4 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 SN74S138ANG4 meets industry standards.
7.What is the process for return or replacement of SN74S138ANG4?
All SN74S138ANG4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74S138ANG4, 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 SN74S138ANG4 part is unused and in its original packaging.
Return procedure for SN74S138ANG4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
SN74S138ANG4 Tags
-
SN74HC138DR
Texas Instruments
-
TC7SB3157CFU,LF(CT
Toshiba Semiconductor and Storage
-
74CBTLV3257PW,118
Nexperia USA Inc.
-
SN74CBTLV3257PWR
Texas Instruments
-
74CBTLV3257GUX
Nexperia USA Inc.
-
74HC154BQ,118
Nexperia USA Inc.
-
P3S0200GMX
NXP USA Inc.
-
SN74CB3Q3245PWR
Texas Instruments
-
SN74CB3Q3257RGYR
Texas Instruments
-
TCA9543APWR
Texas Instruments
-
TCA9546APWR
Texas Instruments
-
SN74HC138N
Texas Instruments
Tech Hub
A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.
The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…
The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…
A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…
A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …
An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…
Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…
An engineering guide to LED driver operation, constant-current and constant-voltage outputs, linear and switching topologies, dimming, IC selection, calculations, replacement compatibility, and fault c…
Operational amplifier guide covering op amp basics, feedback, ideal vs real op amps, common configurations, buffer circuits, offset, bias current, gain-bandwidth, slew rate, rail-to-rail limits and sel…
Jumper cables guide covering safe connection order, red and black clamp placement, final ground connection, cable gauge, length, clamp quality, copper vs CCA cables, jump starter comparison and battery…
