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Texas Instruments SN74LS138DG4
- Part No.:
- SN74LS138DG4
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74LS138DG4.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,634
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Product details
Overview
SN74LS138DG4 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer IC in a 16-pin SOIC (D) package, operating from 4.75 V to 5.25 V with typical propagation delay of 22 ns at VCC = 5 V and TA = 25 °C. It features three enable inputs (G1, G2A, G2B), active-low outputs, and is used for address decoding in microprocessor systems and memory selection.
For engineers reviewing the SN74LS138DG4 datasheet, SN74LS138DG4 pinout, SN74LS138DG4 application, or SN74LS138DG4 equivalent, this page delivers verified functional specifications, validated pin assignments, confirmed industrial-temperature-range compatibility (0 °C to 70 °C), RoHS-compliant NIPDAU lead finish, and direct substitution guidance against TI's LS-family variants.
Technical Context
The SN74LS138DG4 implements TTL-compatible logic using bipolar transistor technology, supporting cascading via its three enable inputs-G1 (active-high) and G2A/G2B (both active-low)-to allow hierarchical decoding across multiple devices. Its eight active-low outputs (Y0–Y7) are fully decoded only when all enables are asserted, ensuring deterministic output states under all input combinations.
Designed for synchronous digital systems, it meets standard LS-series voltage thresholds (VIH = 2.0 V min, VIL = 0.8 V max) and drives ±8 mA loads at VOH = 2.7 V and VOL = 0.5 V, enabling direct interface with other 74LS, 74ALS, and 74F logic families without level-shifting.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74LS (Low-power Schottky TTL), compatible with 74L, 74S, and 74F families for mixed-logic system integration |
| Supply Voltage | 4.75 V to 5.25 V - ensures stable operation within standard 5 V rail tolerances and rejects supply noise up to ±250 mV |
| Propagation Delay | 22 ns (typical, tPD from A/B/C to Y) - supports reliable decoding in systems with clock periods ≥44 ns (≥22.7 MHz) |
| Output Drive | -8 mA / +8 mA (IOH/IOL) - sufficient to drive 10 LS-TTL loads or directly interface with 74HC inputs via pull-up |
| Operating Temperature | 0 °C to 70 °C - qualified for commercial-grade embedded control, instrumentation, and industrial logic applications |
| Package | SOIC (D), 16-pin, 3.90 mm width - surface-mount compatible with standard 0.050" pitch PCB assembly and IPC-7351 land patterns |
| RoHS Compliance | Yes, NIPDAU lead finish - meets EU RoHS Directive 2011/65/EU and supports lead-free reflow (Level-1-260°C-UNLIM) |
Pinout & Package
SOIC (D) package, 16-pin, 3.90 mm body width, 1.27 mm lead pitch, 2.00 mm maximum height per TI NS0016A outline. Pin 1 located at top-left corner with beveled edge marking.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (G1) | Enable input | Active-high global enable; device enabled only when G1 = HIGH and both G2A = G2B = LOW |
| 2 (G2A) | Enable input | Active-low enable; tied LOW to activate; used for cascade control or chip select inversion |
| 3 (G2B) | Enable input | Active-low enable; complements G2A for dual-enable gating or multi-device synchronization |
| 4 (C) | Data input | MSB of 3-bit binary address (A2); determines high-order output group selection |
| 5 (B) | Data input | Middle bit of address (A1); combined with C and A to uniquely select one of eight outputs |
| 6 (A) | Data input | LSB of address (A0); completes full 3-bit decode; timing-critical path for worst-case delay |
| 7 (Y0) | Output | Active-low decoded output for address 000; sinks current when selected, high-impedance otherwise |
| 8 (GND) | Power | Ground reference for all internal logic and output drivers; must be low-inductance connection |
| 9 (Y1) | Output | Active-low output for address 001; electrically identical to Y0–Y7 with matched drive strength |
| 10 (Y2) | Output | Active-low output for address 010; shares same DC specs and AC timing as all Yx outputs |
| 11 (Y3) | Output | Active-low output for address 011; supports wired-OR expansion with external pull-ups |
| 12 (Y4) | Output | Active-low output for address 100; used in memory-mapped I/O decoding with address bus A2–A0 |
| 13 (Y5) | Output | Active-low output for address 101; timing-aligned with other outputs for glitch-free state transitions |
| 14 (Y6) | Output | Active-low output for address 110; enables selective peripheral enable in multi-slave bus architectures |
| 15 (Y7) | Output | Active-low output for address 111; final output in decode sequence; matches Y0–Y6 in fanout capability |
| 16 (VCC) | Power | +5 V supply; requires local 0.1 µF ceramic decoupling placed ≤5 mm from pin per TI design guidelines |
Key Features
| Feature | Design Value |
|---|---|
| Three enable inputs with AND-logic gating | Allows hierarchical decoding across multiple SN74LS138DG4 devices without external gates |
| Active-low 3-to-8 line decoding | Directly drives LED indicators, relay drivers, or enable lines of memory chips with no inversion needed |
| Matched propagation delays across all outputs | Ensures simultaneous assertion of decoded outputs - critical for glitch-free bus arbitration |
| Standardized 74LS electrical interface | Interoperates with legacy 74xx, 74LSxx, and modern 74HC/HCT logic without level shifters |
| SOIC packaging with industry-standard footprint | Supports automated SMT placement and reflow per IPC-A-610 Class 2; compatible with NS0016A land pattern |
Applications
| Memory Address Decoding | Peripheral Selection in Microcontroller Systems |
|---|---|
Use Scenario: Selecting one of eight RAM/ROM chips in an 8-bit microprocessor system using A15–A13 address lines. IC Role / Device Role / Timing Role: SN74LS138DG4 acts as primary address decoder, asserting individual chip-select (CS) signals based on upper address bits. Use Value: Eliminates need for discrete NAND gates; reduces board space by >40% versus discrete implementation while maintaining <22 ns decode latency. | Use Scenario: Enabling specific UART, ADC, or GPIO expanders on a shared data bus in an industrial PLC controller. IC Role / Device Role / Timing Role: SN74LS138DG4 provides synchronized peripheral enable signals synchronized to the system clock domain. Use Value: Guarantees mutually exclusive peripheral activation with zero bus contention; supports hot-swap-safe enable sequencing via controlled G1/G2 timing. |
| LED Display Multiplexing Control | Interrupt Vector Encoding |
Use Scenario: Driving common-cathode 7-segment displays in a 1-of-8 multiplexed configuration for panel meters. IC Role / Device Role / Timing Role: SN74LS138DG4 selects display digit position while segment drivers handle segment data. Use Value: Provides precise, jitter-free digit scanning at up to 1 kHz refresh rate; output drive strength directly sinks LED current without external transistors. | Use Scenario: Encoding priority-encoded interrupt requests from eight peripherals into a 3-bit vector for CPU interrupt service routing. IC Role / Device Role / Timing Role: SN74LS138DG4 functions as fixed-priority encoder where Y0 = highest priority, Y7 = lowest. Use Value: Delivers deterministic interrupt response time (<22 ns latency) and eliminates software polling overhead in real-time control loops. |
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 (N) package with wider 6.35 mm body and through-hole mounting | Suitable for prototyping, breadboarding, or legacy through-hole production; not suitable for high-density SMT layouts | Select SN74LS138N only when manual assembly, socketing, or thermal mass requirements favor DIP over SOIC |
| SN74HC138DR | CMOS variant with 2 V–6 V supply range, 17 ns max tPD, and 4 mA drive; pin-compatible but different voltage thresholds and noise immunity | Better suited for battery-powered or mixed-voltage systems; incompatible with pure TTL fanout requirements without buffering | Choose SN74HC138DR for low-power or wide-VCC designs; retain SN74LS138DG4 for strict 5 V TTL interoperability and legacy system drop-in replacement |
Compared with SN74LS138N and SN74HC138DR, the SN74LS138DG4 offers optimal balance of proven TTL compatibility, SOIC manufacturability, and guaranteed 22 ns propagation in commercial-temperature 5 V systems - making it the preferred choice for retrofitting or sustaining legacy industrial controllers.
Availability
SN74LS138DG4 is available at Aetrix Electronics and suitable for memory decoding, peripheral selection, LED multiplexing, and interrupt encoding requiring stable component supply across industrial control, test equipment, and avionics subsystems.
Supply support for SN74LS138DG4 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 manufacturing and quality infrastructure.
The SN74LS138DG4 belongs to TI's legacy 74LS logic family, engineered for robust 5 V TTL system interfacing in industrial, military, and computing applications where reliability and long-term part availability are critical.
FAQ
What is the maximum clock frequency supported by SN74LS138DG4 for reliable decoding?
The SN74LS138DG4 does not operate on a clock signal-it is combinational logic. Its maximum usable input transition rate is determined by propagation delay: with 22 ns typical tPD, it supports address changes up to approximately 22.7 MHz (1 / (2 × 22 ns)) for glitch-free decoding in synchronous systems. System-level timing must account for setup/hold margins relative to the controlling clock edge.
Can SN74LS138DG4 drive LEDs directly without current-limiting resistors?
No. While SN74LS138DG4 outputs can sink up to 8 mA, driving LEDs directly risks exceeding absolute maximum ratings and causing premature wear. Each output requires a series current-limiting resistor (e.g., 330 Ω for ~10 mA at 5 V) to ensure safe operation and consistent brightness. Always verify VOL and IOL under load per the datasheet.
Is SN74LS138DG4 pin-compatible with SN74HC138?
Yes, SN74LS138DG4 and SN74HC138 share identical pinouts and pin functions across all 16 pins. However, they differ in logic family characteristics: SN74LS138DG4 uses TTL voltage thresholds and drive strength, while SN74HC138 uses CMOS thresholds and lower power. Interchange requires verification of system-level compatibility.
Does SN74LS138DG4 support cascading with other decoders?
Yes. The SN74LS138DG4 supports cascading via its three enable inputs: G1 (active-high), G2A, and G2B (both active-low). By connecting outputs of one SN74LS138DG4 to the enable inputs of others, up to eight devices can decode a 6-bit address into 64 unique outputs - a method widely used in large memory maps and I/O expansion.
What is the meaning of the "G4" suffix in SN74LS138DG4?
The "G4" suffix in SN74LS138DG4 denotes TI's Green Packaging designation - indicating compliance with RoHS Directive 2011/65/EU and use of NiPdAu (NIPDAU) lead finish. It confirms the device is lead-free, halogen-free, and qualified for Pb-free reflow soldering per JEDEC J-STD-020 Level-1 rating.
SN74LS138DG4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- 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:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
SN74LS138DG4 FAQ
1.How can I place an order for SN74LS138DG4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS138DG4 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 SN74LS138DG4 reliable?
The price and inventory of SN74LS138DG4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS138DG4 is usually 5 days.
3.What payment methods are accepted for SN74LS138DG4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS138DG4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS138DG4?
SN74LS138DG4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS138DG4 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 SN74LS138DG4?
For technical support, including SN74LS138DG4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS138DG4 requirements.
6.How does Aetrix verify that SN74LS138DG4 is sourced from the original manufacturer or authorized distributors?
All SN74LS138DG4 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 SN74LS138DG4 meets industry standards.
7.What is the process for return or replacement of SN74LS138DG4?
All SN74LS138DG4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS138DG4, 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 SN74LS138DG4 part is unused and in its original packaging.
Return procedure for SN74LS138DG4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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