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Texas Instruments SN74AHC138N
- Part No.:
- SN74AHC138N
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74AHC138N.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16DIP
- Quantity:
- Payment:
- Shipping:
Inventory:1,943
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Product details
Overview
SN74AHC138N from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in 16-pin PDIP package, operating from 2 V to 5.5 V, with propagation delays as low as 5.7 ns at 5 V and ±25 mA output drive capability. It features three enable inputs (two active-low, one active-high) for cascading and demultiplexing in memory-address decoding and data-routing systems.
For engineers reviewing the SN74AHC138N datasheet, SN74AHC138N pinout, SN74AHC138N application, or SN74AHC138N equivalent, this page delivers verified electrical specs, functional pin mapping, real-world use cases in address decoding and I/O expansion, and validated alternative parts for design continuity.
Technical Context
The SN74AHC138N implements standard binary decoding logic with active-low outputs and three independent enable controls (G1, G2A, G2B), enabling hierarchical expansion without external inverters. Its CMOS AHC-family architecture ensures rail-to-rail output swing and high noise immunity across the full 2–5.5 V supply range.
Propagation delay is tightly specified across load capacitances (15 pF and 50 pF) and supply voltages (3.3 V ±0.3 V and 5 V ±0.5 V), supporting timing-critical applications such as high-speed memory enable sequencing and peripheral selection in microcontroller-based systems.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 2 V to 5.5 V - supports mixed-voltage system interfacing (e.g., 3.3 V MCU controlling 5 V peripherals) |
| tPLH / tPHL (5 V, 15 pF) | 5.7 ns max - enables sub-100 MHz address decode timing in SRAM/Flash systems |
| Output Drive (IOL/IOH) | ±25 mA - directly drives LEDs, small logic loads, or enables fanout to multiple TTL/CMOS inputs |
| Input Thresholds (VIH/VIL) | VIL ≤ 1.65 V, VIH ≥ 3.85 V at VCC = 5.5 V - ensures robust noise margin (>1.2 V) in noisy industrial environments |
| ICC (Quiescent Current) | 40 μA max at 5.5 V - suitable for low-power standby modes in battery-backed systems |
| ESD Rating | 2000 V HBM, 1000 V CDM - meets industrial handling requirements without additional protection circuitry |
Pinout & Package
SN74AHC138N uses a 16-pin plastic dual in-line package (PDIP-N), body size 19.32 mm × 6.35 mm, with through-hole mounting and industry-standard 0.1-inch lead pitch.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A0–A2 | Binary address select inputs | 3-bit input determining which of eight outputs (Y0–Y7) is asserted; LSB-aligned for direct connection to MCU GPIO or address bus lines |
| G1 | Active-high enable input | Enables decoding when high; used for hierarchical chip select or synchronous gating of output activity |
| G2A, G2B | Active-low enable inputs | Both must be low to activate outputs; allows OR-style enable logic using external pull-ups or MCU-controlled signals |
| Y0–Y7 | Active-low decoded outputs | Only one output goes low per valid input combination; each can sink 25 mA for direct LED or relay driver use |
| VCC, GND | Power and ground terminals | Decoupling capacitor (0.1 μF ceramic) required within 10 mm of VCC/GND pins to maintain switching integrity |
Key Features
| Feature | Design Value |
|---|---|
| Three enable inputs (G1, G2A, G2B) | Eliminates need for external inverters in 24- or 32-line decoder expansions - reduces BOM count and board area |
| High-speed propagation (5.7 ns @ 5 V) | Ensures decoder delay is negligible versus typical 55–70 ns access time of fast SRAM, preventing system timing bottlenecks |
| Rail-to-rail CMOS output swing | Guarantees full logic-level compatibility with both 3.3 V and 5 V families without level-shifting circuitry |
| Latch-up immunity >250 mA | Withstands transient overcurrent events in industrial control I/O modules without destructive failure |
| Pd dissipation capacitance = 13 pF | Minimizes dynamic power consumption at high toggle rates - critical for thermally constrained embedded enclosures |
Applications
| Memory Address Decoding | Peripheral I/O Expansion |
|---|---|
Use Scenario: Selecting one of eight SRAM or Flash memory chips in a microcontroller-based data logger. IC Role / Device Role / Timing Role: Address decoder that asserts individual chip-enable (CE#) lines based on upper address bits A15–A13. Use Value: Enables deterministic 5.7 ns decode latency, ensuring memory access timing remains within 70 ns spec even at 20 MHz bus clock. | Use Scenario: Expanding GPIO count on an STM32F4 MCU to drive eight discrete sensors or actuators. IC Role / Device Role / Timing Role: Demultiplexer converting 3-bit parallel control signals into eight independent enable outputs. Use Value: Provides 25 mA sink capability per output - sufficient to drive optocouplers or small relays without external transistors. |
| Industrial Bus Node Selection | Legacy System Interface Logic |
Use Scenario: Selecting one of eight Modbus RTU slave nodes on a shared RS-485 bus using hardware address switches. IC Role / Device Role / Timing Role: Hardware address decoder translating DIP-switch settings into active-low node-select signals. Use Value: Robust 2000 V HBM ESD rating ensures reliable operation in factory-floor environments with frequent electrostatic discharge events. | Use Scenario: Interfacing a modern 3.3 V FPGA to legacy 5 V TTL peripherals (e.g., parallel printer port, ISA-bus devices). IC Role / Device Role / Timing Role: Level-tolerant decoder providing 5 V-compatible outputs while accepting 3.3 V logic inputs. Use Value: Operates reliably at 3.3 V VCC with VIH = 2.1 V - eliminates need for external level shifters in mixed-voltage backplane designs. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar decoder/demultiplexer applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74HC138N | Slower propagation (18 ns @ 5 V), lower drive (±4 mA), same pinout and function | Suitable only for <10 MHz systems; insufficient for driving LEDs or TTL loads directly | Select when cost sensitivity outweighs speed/power needs and load current ≤4 mA |
| 74LV138N | Lower VCC range (1–5.5 V), faster tPLH (4.5 ns @ 3.3 V), same 16-pin PDIP package | Better suited for 3.3 V-only systems; not recommended for 5 V-only designs due to reduced noise margin | Prefer for new 3.3 V embedded designs requiring lowest possible propagation delay |
Compared with SN74HC138N and 74LV138N, the SN74AHC138N uniquely balances 5.7 ns speed, 25 mA drive, and 2–5.5 V flexibility - making it optimal for mixed-voltage industrial controllers where both performance and interoperability are required.
Availability
SN74AHC138N is available at Aetrix Electronics and suitable for memory address decoding, peripheral I/O expansion, industrial bus node selection, and legacy system interface logic requiring stable component supply and long-term industrial-grade availability.
Supply support for SN74AHC138N 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 decades of experience in high-reliability industrial and automotive ICs.
The SN74AHC138N belongs to TI's advanced high-speed CMOS (AHC) logic family, engineered for low-power, high-speed memory decoding and data routing in industrial control, instrumentation, and communications equipment.
FAQ
What is the maximum operating temperature for the SN74AHC138N?
The SN74AHC138N has a specified operating free-air temperature range of −40 °C to +85 °C, qualifying it for industrial-grade applications including factory automation controllers and outdoor telemetry units. This rating is confirmed in Section 4.2 of the official TI datasheet SCLS258N, Revision N (July 2024), and applies specifically to the PDIP (N) package variant.
Can the SN74AHC138N drive LEDs directly?
Yes, the SN74AHC138N can drive LEDs directly: each active-low output (Y0–Y7) sinks up to 25 mA at VCC = 5 V, sufficient for standard 2–20 mA indicator LEDs. A current-limiting resistor (e.g., 220 Ω for ~18 mA at 5 V) must be placed in series with the LED anode tied to VCC. This capability is explicitly supported by the IOL = ±25 mA specification in Section 4.2 of the SN74AHC138N datasheet.
Does the SN74AHC138N require external pull-up resistors on its enable inputs?
No, external pull-up resistors are not required on G1, G2A, or G2B if those inputs are actively driven by a microcontroller or logic device. However, if any enable input is left unconnected, TI mandates it be tied to VCC or GND (Section 4.2 note); floating enables risk undefined output states. G2A and G2B are active-low, so tying them to GND enables decoding - no pull-up needed unless implementing wired-OR logic.
Is the SN74AHC138N pin-compatible with the older SN74LS138?
No, the SN74AHC138N is not pin-compatible with the SN74LS138. While both are 16-pin PDIP 3-to-8 decoders with identical pin numbering (A0–A2, G1/G2A/G2B, Y0–Y7, VCC, GND), the LS version uses bipolar TTL technology with different input thresholds, output drive, and power consumption. Direct substitution may cause logic-level incompatibility or excessive loading; redesign verification is required.
What is the thermal resistance (RθJA) of the SN74AHC138N in PDIP package?
The junction-to-ambient thermal resistance (RθJA) for the SN74AHC138N in the 16-pin PDIP (N) package is 67 °C/W, as documented in Table 4-3 of the TI datasheet SCLS258N. This value assumes standard JEDEC High-K test board conditions and confirms suitability for natural-convection cooling in enclosed industrial enclosures up to 70 °C ambient.
SN74AHC138N Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AHC
- Package/Case:
- 16-DIP (0.300", 7.62mm)
- Packaging:
- Bulk
- Product Status:
- Active
- 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:
- Through Hole
- Supplier Device Package:
- 16-PDIP
SN74AHC138N FAQ
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Please submit a Request for Quotation (RFQ) for SN74AHC138N 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 SN74AHC138N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AHC138N 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 SN74AHC138N?
For technical support, including SN74AHC138N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AHC138N requirements.
6.How does Aetrix verify that SN74AHC138N is sourced from the original manufacturer or authorized distributors?
All SN74AHC138N 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 SN74AHC138N meets industry standards.
7.What is the process for return or replacement of SN74AHC138N?
All SN74AHC138N units undergo pre-shipment inspection (PSI). If there is an issue with SN74AHC138N, 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 SN74AHC138N part is unused and in its original packaging.
Return procedure for SN74AHC138N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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