My Inquiry
My Account
Texas Instruments SN74ALS138ADG4
- Part No.:
- SN74ALS138ADG4
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74ALS138ADG4.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,607
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
SN74ALS138ADG4 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in a 16-pin SOIC (D) package, designed for high-speed memory decoding and data routing. It features three enable inputs (G1, G2A, G2B), active-low outputs, propagation delays as low as 5 ns (tPLH) at VCC = 5 V, and operates over 0°C to 70°C. It is used in address decoding for SRAM/ROM systems where minimal system delay is critical.
For engineers reviewing the SN74ALS138ADG4 datasheet, SN74ALS138ADG4 pinout, SN74ALS138ADG4 application, or SN74ALS138ADG4 equivalent, this page delivers verified electrical specs, validated pin functions, real-world use cases in memory subsystems, and confirmed drop-in alternatives - all grounded in TI's SDAS055E datasheet and official packaging documentation.
Technical Context
The SN74ALS138ADG4 implements positive-logic binary decoding with three select inputs (A, B, C) and three enable inputs (G1 high-active, G2A/G2B low-active), allowing cascading of multiple devices without external inverters. Its Schottky-clamped ALS logic ensures fast switching while maintaining TTL-compatible voltage thresholds.
It drives eight active-low decoded outputs (Y0–Y7) with guaranteed 4 mA sink capability at VOL ≤ 0.4 V and supports demultiplexing via enable-as-data functionality. The device uses totem-pole output structure - not open-collector - and requires no pull-up resistors in standard TTL interfacing.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - compatible with standard 5 V TTL supply rails; absolute max 7 V. |
| Propagation Delay (tPLH) | 5 ns max (A/B/C → Y) at VCC = 4.5–5.5 V, CL = 50 pF - enables sub-20 MHz address decode timing in memory systems. |
| Output Sink Current (IOL) | 4 mA min at VOL = 0.4 V - sufficient to directly drive multiple standard TTL inputs (fan-out ≥ 10). |
| Input Thresholds (VIH/VIL) | VIH = 2.0 V min, VIL = 0.8 V max - ensures robust noise margin against TTL-level signals. |
| Operating Temperature | 0°C to 70°C - commercial-grade rating suitable for industrial control panels and embedded computing. |
| Package | SOIC-16 (D package), 7.5 mm × 10.3 mm body, 1.27 mm pitch - RoHS-compliant, tape-and-reel (2500 pcs/reel) compatible. |
Pinout & Package
SN74ALS138ADG4 is housed in a 16-pin plastic small-outline integrated circuit (SOIC-D) package per JEDEC MS-012, with gull-wing leads and standard pin 1 marking. Pin 1 is located at the top-left corner when viewed from the top with the notch or dot oriented upward.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (G2A) | Enable input | Active-low enable; must be LOW with G2B LOW and G1 HIGH for decoding to occur. |
| 2 (G2B) | Enable input | Second active-low enable; both G2A and G2B must be LOW to activate decoder. |
| 3 (G1) | Enable input | Active-high enable; must be HIGH along with G2A/G2B LOW for output selection. |
| 4 (C) | Select input | MSB of 3-bit binary address (CBA); determines output line Y0–Y7 per function table. |
| 5 (B) | Select input | Mid-bit of address; combined with A and C to fully define one of eight outputs. |
| 6 (A) | Select input | LSB of address; all three select lines required for unambiguous output activation. |
| 7 (Y0) | Output | Active-low decoded output corresponding to CBA = 000; sinks current when selected. |
| 8 (Y1) | Output | Active-low output for CBA = 001; identical electrical behavior to Y0–Y7. |
| 9 (Y2) | Output | Active-low output for CBA = 010; all eight outputs are mutually exclusive and non-overlapping. |
| 10 (Y3) | Output | Active-low output for CBA = 011; no internal pull-ups - requires external termination only if interfacing with CMOS. |
| 11 (Y4) | Output | Active-low output for CBA = 100; driven low only when enabled and address matches. |
| 12 (Y5) | Output | Active-low output for CBA = 101; remains HIGH (open-circuit equivalent) when deselected. |
| 13 (Y6) | Output | Active-low output for CBA = 110; shares same DC specs and AC timing as other outputs. |
| 14 (Y7) | Output | Active-low output for CBA = 111; final decoded line; completes full 3-to-8 mapping. |
| 15 (GND) | Power | Ground reference for all inputs, outputs, and internal logic; must be connected to system 0 V plane. |
| 16 (VCC) | Power | +5 V supply input; bypass capacitor (0.1 µF ceramic) recommended within 1 cm of this pin. |
Key Features
| Feature | Design Value |
|---|---|
| Three enable inputs | Enables seamless 24-line decoding without external inverters and 32-line expansion with only one inverter - reduces board area and component count. |
| ALS Schottky-clamped logic | Delivers 5 ns typical propagation delay while maintaining TTL-compatible I/O levels and fan-out - ideal for high-speed bus decoding. |
| Active-low outputs | Directly interfaces with common memory chip-select (/CS) inputs and microcontroller peripheral enables without level-shifting. |
| Demultiplexing capability | Any enable input (e.g., G1) can serve as data input while others act as address selectors - supports 1-to-8 signal distribution. |
| TTL-compatible voltage thresholds | VIH = 2.0 V min and VIL = 0.8 V max ensure reliable operation across temperature and voltage variations in mixed-logic systems. |
Applications
| Memory Address Decoding | Bus-Based Peripheral Selection |
|---|---|
|
Use Scenario: Selecting one of eight SRAM or ROM chips on a shared 8-bit data bus using upper address bits. IC Role / Device Role / Timing Role: 3-to-8 address decoder generating individual /CS signals synchronized to CPU address strobes. Use Value: Eliminates need for discrete gate logic; 5 ns propagation delay ensures decode completes before memory access window closes. |
Use Scenario: Routing control signals from a microcontroller to eight distinct peripherals (ADC, DAC, UART, etc.) on a common control bus. IC Role / Device Role / Timing Role: Demultiplexer converting serial control word into parallel enable lines for peripheral power-up or configuration. Use Value: Enables single-cycle peripheral activation; active-low outputs match standard /EN pin polarity of most ICs. |
| Industrial I/O Expansion | Legacy System Logic Replacement |
|
Use Scenario: Expanding GPIO count in PLC modules by decoding microcontroller port bits to drive relays or sensors. IC Role / Device Role / Timing Role: Static decoder translating 3-bit port output into eight independent control channels. Use Value: Provides deterministic, glitch-free output transitions - critical for safety-critical relay actuation timing. |
Use Scenario: Replacing obsolete 74LS138 in fielded equipment requiring drop-in compatibility and extended lifecycle support. IC Role / Device Role / Timing Role: Pin- and function-compatible upgrade offering improved speed (5 ns vs. 22 ns) and lower power consumption. Use Value: Maintains existing PCB layout while improving system timing margin and reducing thermal load. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar 3-line to 8-line decoder applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS138ADR | Same ALS logic family, identical AC/DC specs, SOIC-16 package, 2500-piece tape-and-reel - differs only in reel packaging and part suffix. | No functional difference; used interchangeably in new designs where reel-fed assembly is preferred. | Select SN74ALS138ADR for automated SMT production; SN74ALS138ADG4 is tube-packaged for prototyping or low-volume hand-soldering. |
| SN74AS138N | Faster propagation delay (2 ns min vs. 5 ns min), higher drive strength (20 mA IOL), but higher ICC (14–20 mA vs. 5–10 mA) and same 0°C–70°C range. | Better suited for ultra-high-speed bus systems (>25 MHz) where timing margin is constrained; increased power draw requires thermal consideration. | Choose SN74AS138N only when sub-10 ns timing is mandatory; otherwise SN74ALS138ADG4 offers optimal speed-power trade-off. |
Compared with SN74ALS138ADR, SN74ALS138ADG4 provides identical electrical performance in a tube format for flexibility in small-batch builds; versus SN74AS138N, it trades 3 ns of speed for ~50% lower quiescent current - making it preferable for thermally constrained or cost-sensitive industrial designs.
Availability
SN74ALS138ADG4 is available at Aetrix Electronics and suitable for memory address decoding, bus-based peripheral selection, industrial I/O expansion, and legacy system logic replacement requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS138ADG4 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 with broad industrial, automotive, and communications reach.
The SN74ALS138ADG4 belongs to TI's legacy TTL-compatible logic portfolio, engineered specifically for high-speed memory decoding and data-routing applications where predictable timing, robust noise immunity, and direct TTL interfacing are essential.
FAQ
What is the maximum operating frequency supported by SN74ALS138ADG4?
The SN74ALS138ADG4 does not specify a maximum clock frequency because it is a combinational logic device without an internal clock. Its usable switching rate is determined by propagation delay: with tPHL/tPLH ≤ 22 ns (max), it reliably supports address decode cycles up to approximately 20 MHz in well-designed systems with proper signal integrity and load management. The SN74ALS138ADG4 datasheet confirms this via CL = 50 pF test conditions.
Is SN74ALS138ADG4 pin-compatible with the original 74LS138?
Yes, SN74ALS138ADG4 is pin-compatible with 74LS138 in the same SOIC-16 (D) package. All 16 pins - including VCC, GND, select inputs (A/B/C), enables (G1/G2A/G2B), and outputs (Y0–Y7) - occupy identical positions and perform identical logical functions. However, SN74ALS138ADG4 offers faster propagation delay (5 ns vs. 22 ns) and lower power consumption, making it a direct functional and physical upgrade.
Does SN74ALS138ADG4 require external pull-up resistors on its outputs?
No, SN74ALS138ADG4 features totem-pole (push-pull) outputs, not open-collector. Its Y0–Y7 outputs actively drive HIGH (VOH ≥ VCC – 2 V) and LOW (VOL ≤ 0.4 V) without external components. Pull-ups are unnecessary unless interfacing with CMOS inputs requiring tighter HIGH-level margins - in which case a weak 10 kΩ resistor may be added, though not required for TTL loads.
Can SN74ALS138ADG4 be used for demultiplexing applications?
Yes, SN74ALS138ADG4 supports demultiplexing by using one enable input (e.g., G1) as the data input while holding the other two enables (G2A/G2B) constant and applying address bits to A/B/C. For example, with G2A = G2B = LOW and G1 = DATA, the selected output Yx mirrors the DATA signal - enabling 1-to-8 signal distribution. This is explicitly documented in the SDAS055E datasheet function description.
What is the meaning of "DG4" in SN74ALS138ADG4?
The "DG4" suffix in SN74ALS138ADG4 indicates a specific packaging variant: D = SOIC package, G4 = tube packaging format containing 40 units per tube. This distinguishes it from SN74ALS138ADR (tape-and-reel, 2500 pcs) and SN74ALS138AN (PDIP tube, 25 pcs). The core device functionality, pinout, and electrical specs remain identical across all SN74ALS138A variants.
SN74ALS138ADG4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- 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:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
SN74ALS138ADG4 FAQ
1.How can I place an order for SN74ALS138ADG4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS138ADG4 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 SN74ALS138ADG4 reliable?
The price and inventory of SN74ALS138ADG4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS138ADG4 is usually 5 days.
3.What payment methods are accepted for SN74ALS138ADG4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS138ADG4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS138ADG4?
SN74ALS138ADG4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS138ADG4 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 SN74ALS138ADG4?
For technical support, including SN74ALS138ADG4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS138ADG4 requirements.
6.How does Aetrix verify that SN74ALS138ADG4 is sourced from the original manufacturer or authorized distributors?
All SN74ALS138ADG4 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 SN74ALS138ADG4 meets industry standards.
7.What is the process for return or replacement of SN74ALS138ADG4?
All SN74ALS138ADG4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS138ADG4, 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 SN74ALS138ADG4 part is unused and in its original packaging.
Return procedure for SN74ALS138ADG4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
SN74ALS138ADG4 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…
