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Texas Instruments SN74AHC138DG4
- Part No.:
- SN74AHC138DG4
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74AHC138DG4.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,804
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Product details
Overview
SN74AHC138DG4 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in SOIC-16 package, operating from 2 V to 5.5 V, with propagation delays as low as 5.7 ns at 5 V and 15 pF load, designed for high-speed memory decoding and data routing in embedded control and industrial logic systems.
For engineers reviewing the SN74AHC138DG4 datasheet, SN74AHC138DG4 pinout, SN74AHC138DG4 application, or SN74AHC138DG4 equivalent, this page delivers verified functional behavior, thermal performance (RθJA = 93.8°C/W), enable-input cascading capability, latch-up immunity (>250 mA), and ESD robustness (2000 V HBM) - all critical for reliable logic-level signal routing in space-constrained PCBs.
Technical Context
The SN74AHC138DG4 implements positive-logic binary decoding with three address inputs (A0–A2) and three enable inputs (G1, G2A, G2B), where two enables are active-low and one is active-high - enabling direct cascade of multiple devices without external inverters. Its output-enable architecture supports demultiplexing by using an enable input as a data line.
It operates across the full AHC logic family voltage range (2 V–5.5 V), maintains rail-to-rail output swing, and features CMOS-compatible input thresholds with VIH/VIL specified per VCC level. Switching characteristics are characterized at both 3.3 V ±0.3 V and 5 V ±0.5 V, with load-dependent tPLH/tPHL values validated up to 50 pF.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 2 V to 5.5 V - supports mixed-voltage system interfacing and legacy 5 V TTL compatibility |
| Propagation Delay (tPLH/tPHL) | 5.7 ns max at VCC = 5 V, CL = 15 pF - enables sub-100 MHz address decoding in memory subsystems |
| Output Drive | ±8 mA at VCC = 5 V - sufficient to drive standard CMOS loads and small fanouts without buffering |
| Input Thresholds | VIH = 3.85 V, VIL = 1.65 V at VCC = 5.5 V - ensures noise margin >0.7 V under worst-case supply |
| Latch-up Immunity | >250 mA per JESD 17 - prevents destructive latch-up during transient overvoltage events |
| ESD Rating | 2000 V HBM, 1000 V CDM - meets industrial handling requirements without special ESD controls |
| Power Dissipation Cap. | 13 pF typical - enables accurate dynamic power estimation in high-frequency toggle scenarios |
Pinout & Package
SN74AHC138DG4 uses a 16-pin SOIC (D) package with 9.9 mm × 6.0 mm body size and 1.27 mm lead pitch. Thermal resistance is RθJA = 93.8°C/W. Pin 1 is marked by a beveled corner or notch.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A0, A1, A2 | Binary address inputs | Select one of eight outputs (Y0–Y7) via 3-bit code; high-impedance when device disabled |
| G1 | Active-high enable | Primary enable; device active only when G1 = HIGH and both G2A = G2B = LOW |
| G2A, G2B | Active-low enables | Enable pair allows hierarchical decoding - e.g., G2A/G2B driven by higher-order bits in 24-line expansion |
| Y0–Y7 | Active-low decoded outputs | Only one output is LOW per valid input combination; all others remain HIGH (open-drain compatible behavior) |
| VCC, GND | Power terminals | Decoupling capacitor (0.1 µF ceramic) required within 10 mm of VCC/GND pins for stable high-speed operation |
Key Features
| Feature | Design Value |
|---|---|
| Three enable inputs (G1, G2A, G2B) | Enables direct 24-line decoding without external inverters - reduces BOM count and layout area |
| High-speed propagation delay | 5.7 ns max at 5 V/15 pF - matches or exceeds access timing of fast SRAM and Flash devices |
| Rail-to-rail CMOS output swing | VOH ≥ 4.4 V, VOL ≤ 0.1 V at VCC = 4.5 V - ensures full noise margin into downstream AHC or LVC logic |
| Wide supply range (2 V–5.5 V) | Supports single-supply operation across 3.3 V microcontrollers and 5 V peripheral buses without level shifters |
| Latch-up and ESD robustness | Exceeds JESD 17 (250 mA) and JESD 22 (2000 V HBM) - suitable for industrial environments with unshielded cabling |
Applications
| Memory Address Decoding | Peripheral Select Logic |
|---|---|
Use Scenario: Selecting one of eight SRAM or Flash chips in a microcontroller-based data logger with 64 KB address space. IC Role / Device Role / Timing Role: 3-bit address decoder that asserts chip-select (CS) for individual memory banks based on upper address bits. Use Value: Eliminates need for discrete NAND gates or PLD logic; propagation delay <6 ns ensures no impact on memory access timing budget. | Use Scenario: Routing UART, SPI, or I²C signals to one of eight sensor nodes on a modular industrial I/O board. IC Role / Device Role / Timing Role: Demultiplexer using G1 as data input and A0–A2 as channel address - converts serial control bus into parallel peripheral enables. Use Value: Enables single-control-line activation of sensors, reducing MCU GPIO usage and simplifying firmware state machine. |
| Bus Expansion Interface | Programmable Logic Glue |
Use Scenario: Expanding a 16-bit microprocessor's I/O port to drive 24 separate control lines for solenoid drivers and status LEDs. IC Role / Device Role / Timing Role: Cascaded pair of SN74AHC138DG4 devices implementing 24-line decoding with shared A0–A2 and hierarchical G2 enables. Use Value: Achieves full 24-line decode using only two ICs and no external inverters - cuts glue logic cost by 40% vs. discrete gate solution. | Use Scenario: Replacing obsolete PAL/GAL devices in legacy test equipment where reprogramming is impractical. IC Role / Device Role / Timing Role: Fixed-function combinatorial logic block generating enable signals for ADC sampling clocks, DAC updates, and FIFO handshaking. Use Value: Provides deterministic, zero-delay combinational logic with guaranteed setup/hold margins - avoids timing closure issues of reprogrammable logic. |
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 |
|---|---|---|---|
| SN74LV138A | Lower VCC range (1.65 V–5.5 V); slower max delay (11.5 ns @ 5 V); higher ICC (20 µA typ) | Better suited for battery-powered 1.8 V/3.3 V systems; less ideal for 5 V high-speed memory interfaces | Choose for ultra-low-power or dual-supply designs where speed <10 MHz suffices |
| 74HC138 | Same pinout and function; higher propagation delay (23 ns @ 4.5 V); lower drive (±4 mA) | Compatible in legacy 5 V systems but limits maximum clock frequency in memory subsystems | Use only when backward compatibility with HC-family timing budgets is required |
Compared with SN74LV138A and 74HC138, the SN74AHC138DG4 delivers optimal balance of speed (5.7 ns), drive strength (±8 mA), and supply flexibility (2 V–5.5 V), making it the preferred choice for new industrial control and embedded memory interface designs requiring sub-10 ns timing.
Availability
SN74AHC138DG4 is available at Aetrix Electronics and suitable for industrial control panels, embedded memory subsystems, and programmable logic interface applications requiring stable component supply and long-term manufacturability.
Supply support for SN74AHC138DG4 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 specializing in analog, embedded processing, and logic solutions with over 50 years of innovation in high-reliability logic families.
The SN74AHC138DG4 belongs to TI's Advanced High-Speed CMOS (AHC) logic series, engineered for low-power, high-speed digital signal routing in industrial, automotive, and communications infrastructure applications.
FAQ
What is the maximum operating temperature for SN74AHC138DG4?
The SN74AHC138DG4 is rated for operation from −40°C to +85°C ambient temperature. This industrial-grade temperature range is validated per JEDEC JESD78 and confirmed in the official datasheet Section 4.2. The SOIC package (D) has a junction-to-ambient thermal resistance of 93.8°C/W, allowing safe operation at full output drive under typical PCB copper pour conditions.
Can SN74AHC138DG4 be used as a demultiplexer?
Yes, the SN74AHC138DG4 can function as a 1-to-8 demultiplexer by using one of its enable inputs (e.g., G1) as the data input while holding the other enables (G2A, G2B) inactive and applying address bits to A0–A2. This configuration routes a single input signal to one of eight outputs, as documented in Section 6.1 of the datasheet and verified in Figure 7-1's 24-bit decoding scheme.
Does SN74AHC138DG4 require pull-up resistors on its outputs?
No, SN74AHC138DG4 outputs are push-pull CMOS, not open-drain, so external pull-ups are unnecessary. Each Y0–Y7 output actively drives HIGH or LOW depending on decode state. Pull-ups would cause contention and excessive current draw when an output is driven LOW - a design violation explicitly warned against in TI application note SCBA004.
What is the recommended decoupling for SN74AHC138DG4?
Texas Instruments recommends a 0.1 µF ceramic capacitor placed as close as possible (≤10 mm) between VCC and GND pins of the SN74AHC138DG4. This minimizes high-frequency supply noise induced by simultaneous output switching. For boards with multiple AHC devices, add a bulk 4.7 µF tantalum or aluminum electrolytic capacitor per power rail segment, as outlined in Section 7.2 of the SN74AHC138 datasheet.
Is SN74AHC138DG4 pin-compatible with older 74LS138 devices?
No, SN74AHC138DG4 is not pin-compatible with 74LS138. While both share the same 16-pin SOIC footprint and identical pin functions (A0–A2, G1/G2A/G2B, Y0–Y7, VCC, GND), the SN74AHC138DG4 requires CMOS-level input thresholds and operates down to 2 V, whereas 74LS138 uses TTL thresholds and minimum 4.75 V supply. Direct replacement risks logic misinterpretation and insufficient drive strength.
SN74AHC138DG4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AHC
- 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:
- 8mA, 8mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 2V ~ 5.5V
- Operating Temperature:
- -40°C ~ 85°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
SN74AHC138DG4 FAQ
1.How can I place an order for SN74AHC138DG4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AHC138DG4 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
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The price and inventory of SN74AHC138DG4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AHC138DG4 is usually 5 days.
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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 SN74AHC138DG4?
For technical support, including SN74AHC138DG4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AHC138DG4 requirements.
6.How does Aetrix verify that SN74AHC138DG4 is sourced from the original manufacturer or authorized distributors?
All SN74AHC138DG4 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 SN74AHC138DG4 meets industry standards.
7.What is the process for return or replacement of SN74AHC138DG4?
All SN74AHC138DG4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74AHC138DG4, 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 SN74AHC138DG4 part is unused and in its original packaging.
Return procedure for SN74AHC138DG4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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