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

Texas Instruments SN74LS138DRG4

Name: SN74LS138DRG4
Brand: Texas Instruments
SKU: SN74LS138DRG4
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: SN74LS138DRG4

Manufacturer:: Texas Instruments

Category:: Signal Switches, Multiplexers, Decoders

Package:: 16-SOIC (0.154", 3.90mm Width)

Datasheet:: SN74LS138DRG4.pdf

Description:: IC DECODER/DEMUX 1X3:8 16SOIC

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Product details

Overview

SN74LS138DRG4 from Texas Instruments is a 3-line-to-8-line decoder/demultiplexer IC in a 16-pin SOIC package, operating from 4.75 V to 5.25 V with typical propagation delay of 22 ns at V_CC = 5 V and T_A = 25 °C. It features three enable inputs (G1, G2A, G2B) and eight active-low decoded outputs (Y0–Y7), used for memory address decoding and data routing in TTL-compatible digital systems.

For engineers reviewing the SN74LS138DRG4 datasheet, SN74LS138DRG4 pinout, SN74LS138DRG4 application, or SN74LS138DRG4 equivalent, this page delivers verified functional specifications, package dimensions, real-world use cases in legacy industrial control and instrumentation, and two validated alternative part numbers with documented electrical and timing differences.

Technical Context

The SN74LS138DRG4 implements standard TTL logic architecture with Schottky-clamped bipolar transistors, supporting wired-AND output expansion via its three active-low enables. Its decoding function maps binary inputs A0–A2 to one of eight mutually exclusive low-level outputs, with all outputs high when any enable condition fails.

Input thresholds are compatible with LS-TTL voltage levels (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V), and output drive capability meets I_OL = 24 mA / I_OH = –0.4 mA at V_CC = 5 V, enabling direct interface with other 74LS-series devices without level-shifting.

Key Specifications

Parameter	Value and Actual Design Meaning
Logic Family	74LS (Low-power Schottky TTL) - ensures compatibility with legacy TTL systems and lower power than standard 74-series.
Supply Voltage	4.75 V to 5.25 V - requires regulated +5 V rail; not tolerant of undervoltage or overvoltage operation.
Propagation Delay	22 ns (max) - defines maximum clock-to-output latency in synchronous address decode paths.
Output Drive	I_OL = 24 mA, I_OH = –0.4 mA - supports fan-out of up to 20 LS-TTL loads per output.
Operating Temperature	0 °C to 70 °C - commercial-grade rating; suitable for non-extended-environment embedded controllers.
Package	SOIC (D), 16-pin - surface-mount footprint with 1.27 mm pitch; compatible with standard reflow profiles (Level-1-260°C-UNLIM).

Pinout & Package

SN74LS138DRG4 is housed in a 16-pin SOIC (D) package measuring 10.4 mm × 5.4 mm × 2.0 mm max height, with gull-wing leads and pin 1 marked by a beveled corner or notch.

Pin/Terminal	Circuit Role	Design Meaning
1 (G1)	Active-high enable	Enables decoding only when high; ties to system address bus MSB or control signal for hierarchical selection.
2 (G2A)	Active-low enable	Must be low to activate; often connected to chip-select or write-enable signals.
3 (G2B)	Active-low enable	Second active-low enable; used with G2A for dual-control gating in multi-chip systems.
4 (C)	MSB input	Most significant address bit input (A2); determines upper/lower half of 8-output space.
5 (B)	Address input	Mid-significance address bit (A1); combines with C and A to select one of eight outputs.
6 (A)	LSB input	Least significant address bit (A0); completes 3-bit binary input vector for full decoding.
7 (Y0)	Active-low output	Low when A2A1A0 = 000; drives memory chip select or peripheral enable lines directly.
8 (GND)	Ground reference	Primary return path for all internal logic and output currents; must be low-impedance.
9 (Y1)	Active-low output	Low when A2A1A0 = 001; used for second device selection in banked memory or I/O mapping.
10 (Y2)	Active-low output	Low when A2A1A0 = 010; supports modular peripheral addressing in microcontroller-based systems.
11 (Y3)	Active-low output	Low when A2A1A0 = 011; enables discrete logic partitioning in state-machine control circuits.
12 (Y4)	Active-low output	Low when A2A1A0 = 100; routes signals to specific UART, timer, or ADC peripherals in legacy designs.
13 (Y5)	Active-low output	Low when A2A1A0 = 101; provides dedicated enable for interrupt controller or DMA channel selection.
14 (Y6)	Active-low output	Low when A2A1A0 = 110; isolates test-mode or diagnostic circuitry during normal operation.
15 (Y7)	Active-low output	Low when A2A1A0 = 111; commonly assigned to highest-priority memory block or boot ROM.
16 (V_CC)	Power supply	+5 V DC supply; requires local 0.1 µF ceramic decoupling capacitor placed within 5 mm of pin.

Key Features

Feature	Design Value
Three enable inputs with independent polarity	Allows hierarchical decoding across multiple SN74LS138DRG4 devices without external logic gates.
Active-low 3-to-8 decoding outputs	Directly interfaces with active-low chip-select inputs on SRAM, EPROM, and peripheral ICs.
TTL-compatible input thresholds	Accepts standard LS-TTL logic levels without level translation, simplifying integration into mixed-logic systems.
24-mA sink capability per output	Drives LEDs, relays, or multiple downstream TTL inputs without external buffers in low-speed applications.
Commercial temperature range (0 °C to 70 °C)	Validated for use in office equipment, test instruments, and industrial control panels with ambient cooling.

Applications

Memory Address Decoding	Peripheral Selection in Microcontroller Systems
Use Scenario: Selecting one of eight 8K-byte memory blocks in an 8085-based system using A15–A13 as inputs and chip-select lines as outputs. IC Role / Device Role / Timing Role: Address decoder that translates upper address bits into discrete chip-select signals with <22 ns latency. Use Value: Eliminates need for discrete NAND/NOT gates while maintaining deterministic setup/hold timing for memory access cycles.	Use Scenario: Routing I/O requests from an 8-bit microcontroller to UART, SPI flash, ADC, and DAC peripherals via dedicated CS lines. IC Role / Device Role / Timing Role: Demultiplexer enabling time-shared bus arbitration between four peripherals using three GPIO pins. Use Value: Reduces GPIO count required for peripheral management and avoids software-controlled bit-banging delays.
Industrial Control Logic	Legacy Test Equipment Signal Routing
Use Scenario: Controlling eight solenoid valves in a PLC rack where each valve corresponds to one decoded output line. IC Role / Device Role / Timing Role: Digital output expander converting parallel control bits into isolated actuator enables. Use Value: Provides galvanically isolated driver stage compatibility when paired with ULN2003 arrays.	Use Scenario: Switching calibration reference signals among eight DMM channels in automated test fixtures. IC Role / Device Role / Timing Role: Precision signal selector ensuring minimal crosstalk and consistent propagation delay across all paths. Use Value: Maintains measurement repeatability by eliminating variable routing delays introduced by multiplexed analog switches.

Memory Address Decoding

Peripheral Selection in Microcontroller Systems

Use Scenario: Selecting one of eight 8K-byte memory blocks in an 8085-based system using A15–A13 as inputs and chip-select lines as outputs.

IC Role / Device Role / Timing Role: Address decoder that translates upper address bits into discrete chip-select signals with <22 ns latency.

Use Value: Eliminates need for discrete NAND/NOT gates while maintaining deterministic setup/hold timing for memory access cycles.

Use Scenario: Routing I/O requests from an 8-bit microcontroller to UART, SPI flash, ADC, and DAC peripherals via dedicated CS lines.

IC Role / Device Role / Timing Role: Demultiplexer enabling time-shared bus arbitration between four peripherals using three GPIO pins.

Use Value: Reduces GPIO count required for peripheral management and avoids software-controlled bit-banging delays.

Industrial Control Logic

Legacy Test Equipment Signal Routing

Use Scenario: Controlling eight solenoid valves in a PLC rack where each valve corresponds to one decoded output line.

IC Role / Device Role / Timing Role: Digital output expander converting parallel control bits into isolated actuator enables.

Use Value: Provides galvanically isolated driver stage compatibility when paired with ULN2003 arrays.

Use Scenario: Switching calibration reference signals among eight DMM channels in automated test fixtures.

IC Role / Device Role / Timing Role: Precision signal selector ensuring minimal crosstalk and consistent propagation delay across all paths.

Use Value: Maintains measurement repeatability by eliminating variable routing delays introduced by multiplexed analog switches.

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	Same logic function and timing, but in 16-pin PDIP package with through-hole mounting and 0–70 °C rating.	Suitable for prototyping, breadboarding, or legacy PCBs requiring through-hole assembly.	Select SN74LS138N when manual soldering, socket-based testing, or mechanical robustness in vibration-prone environments is required.
SN74HC138DR	CMOS version with wider V_CC range (2 V–6 V), lower I_CC, and higher noise immunity, but slower propagation delay (21 ns typical at 4.5 V).	Used in mixed-voltage systems or battery-powered devices where power efficiency outweighs speed requirements.	Choose SN74HC138DR for new designs targeting lower static power, broader supply tolerance, or compatibility with 3.3 V logic families.

Compared with SN74LS138N and SN74HC138DR, the SN74LS138DRG4 offers optimal balance of proven TTL timing, SOIC manufacturability, and drop-in replacement capability in existing 74LS-based production boards - especially where board space and reflow compatibility are critical.

Availability

SN74LS138DRG4 is available at Aetrix Electronics and suitable for industrial control panels, legacy test instrumentation, and microcontroller-based peripheral expansion requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74LS138DRG4 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 and embedded processing technologies with broad portfolio coverage across industrial, automotive, and consumer markets.

The SN74LS138DRG4 belongs to TI's legacy 74LS logic family, designed specifically for reliable, low-cost digital signal routing and address decoding in commercial-grade electronic systems built before the widespread adoption of programmable logic.

FAQ

What is the maximum operating frequency of the SN74LS138DRG4?

The SN74LS138DRG4 does not specify a maximum clock frequency because it is a combinational logic device without internal clocking. Its usable switching rate is limited by propagation delay (22 ns max) and system-level setup/hold timing constraints. In practice, the SN74LS138DRG4 reliably supports address decode operations up to approximately 20 MHz in well-designed TTL systems with controlled trace lengths and proper termination.

Can the SN74LS138DRG4 be used with 3.3 V logic systems?

No, the SN74LS138DRG4 requires a 4.75 V to 5.25 V supply and is not 3.3 V tolerant. Its input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V) may accept 3.3 V logic highs marginally, but output voltage swing (≈0.35 V low, ≈3.4 V high) falls outside 3.3 V logic receiver specifications. For 3.3 V systems, use SN74HC138DR or SN74LVC138A instead of SN74LS138DRG4.

How many SN74LS138DRG4 devices can be cascaded for larger decoding?

Multiple SN74LS138DRG4 devices can be cascaded using their enable inputs: one device acts as a master to control the G1/G2A/G2B enables of up to eight slave SN74LS138DRG4 units, expanding decoding to 3-to-64 lines. This configuration preserves the SN74LS138DRG4's native timing behavior and requires no additional logic gates due to its three independent enable terminals.

Is the SN74LS138DRG4 RoHS compliant?

Yes, the SN74LS138DRG4 is RoHS compliant, as confirmed by Texas Instruments' packaging documentation showing "Yes" under RoHS column and "NIPDAU" (Nickel/Palladium/Gold) lead finish. It meets EU Directive 2011/65/EU requirements and contains no lead, mercury, cadmium, hexavalent chromium, PBB, or PBDE above threshold limits.

What is the meaning of the 'G4' suffix in SN74LS138DRG4?

The 'G4' suffix in SN74LS138DRG4 indicates Green (lead-free) packaging per TI's internal nomenclature, denoting compliance with RoHS and use of matte tin or NiPdAu plating. It is functionally identical to SN74LS138DR but reflects updated environmental compliance labeling - the SN74LS138DRG4 and SN74LS138DR share identical electrical specs, timing, and package dimensions.

SN74LS138DRG4 Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: 74LS

Package/Case:: 16-SOIC (0.154", 3.90mm Width)

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

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:: Surface Mount

Supplier Device Package:: 16-SOIC

SN74LS138DRG4 FAQ

1.How can I place an order for SN74LS138DRG4 through Aetrix?

Please submit a Request for Quotation (RFQ) for SN74LS138DRG4 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 SN74LS138DRG4 reliable?

The price and inventory of SN74LS138DRG4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS138DRG4 is usually 5 days.

3.What payment methods are accepted for SN74LS138DRG4?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS138DRG4 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for SN74LS138DRG4?

SN74LS138DRG4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your SN74LS138DRG4 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 SN74LS138DRG4?

For technical support, including SN74LS138DRG4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS138DRG4 requirements.

6.How does Aetrix verify that SN74LS138DRG4 is sourced from the original manufacturer or authorized distributors?

All SN74LS138DRG4 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 SN74LS138DRG4 meets industry standards.

7.What is the process for return or replacement of SN74LS138DRG4?

All SN74LS138DRG4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS138DRG4, 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 SN74LS138DRG4 part is unused and in its original packaging.

Return procedure for SN74LS138DRG4:

1.Submit a request within 90 days.

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

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