My Inquiry
My Account
Texas Instruments SN74HCT138NE4
- Part No.:
- SN74HCT138NE4
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74HCT138NE4.pdf
- Description:
- 3-LINE TO 8-LINE DECODERS/DEMULT
- Quantity:
- Payment:
- Shipping:
Inventory:3,472
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
SN74HCT138NE4 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in 16-pin PDIP package, operating at 4.5–5.5 V, with 17 ns typical propagation delay, ±4-mA output drive, and TTL-compatible inputs. It serves as a high-speed memory address decoder or data routing switch in microcontroller-based systems requiring precise enable-controlled output selection.
For engineers reviewing the SN74HCT138NE4 datasheet, SN74HCT138NE4 pinout, SN74HCT138NE4 application, or SN74HCT138NE4 equivalent, this page delivers verified electrical specs, functional mode mapping, real-world use cases, and validated alternative options for industrial control, embedded memory expansion, and logic-level signal routing designs.
Technical Context
The SN74HCT138NE4 implements active-low 3-to-8 decoding with three enable inputs (G1, G2A, G2B): one active-high (G1) and two active-low (G2A, G2B), enabling cascading without external inverters. Its function table defines eight mutually exclusive low-active outputs (Y0–Y7) selected by binary inputs A, B, C only when all enables are asserted.
Designed for memory-decoding applications, it minimizes system decoding delay - its 17 ns tpd at 5.5 V and fast enable path ensure total decoder + memory enable time remains below typical memory access time, making system-level delay negligible. Input hold current is ≤1 µA max, supporting clean TTL-voltage interface behavior across –40°C to +85°C.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply voltage | 4.5 V to 5.5 V - compatible with standard 5-V TTL logic rails and immune to minor rail droop during switching. |
| Propagation delay (tpd) | 17 ns typical at VCC = 5.5 V - enables sub-60-MHz synchronous operation in address decode paths. |
| Output drive | ±4 mA at 5 V - directly drives 10 LSTTL loads without buffering, reducing BOM count in legacy logic systems. |
| Input compatibility | TTL-voltage thresholds (VIH = 2.0 V, VIL = 0.8 V) - interoperable with 74LS, 74F, and microcontroller GPIOs without level shifters. |
| Quiescent current (ICC) | 80 µA max - supports low-static-power operation in always-on control logic stages. |
| Operating temperature | –40°C to +85°C - qualified for industrial-grade embedded applications including PLC I/O modules and instrumentation. |
| Input capacitance (Ci) | 10 pF max - limits capacitive loading on driving gates, preserving signal integrity in fan-out-critical buses. |
Pinout & Package
SN74HCT138NE4 uses a 16-pin plastic dual in-line package (PDIP-N), body size 19.31 mm × 6.35 mm, with through-hole mounting and industry-standard 0.1-inch pin pitch. Pin 1 is marked by a notch or dot at the top-left corner of the package.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (G2A) | Active-low enable input | Must be LOW to activate decoding; used with G2B and G1 to gate all outputs - critical for hierarchical decoder expansion. |
| 2 (Y0) | Active-low decoded output | Asserted LOW when A=0, B=0, C=0 and all enables active - drives memory chip-select or peripheral enable lines. |
| 3 (Y1) | Active-low decoded output | Asserted LOW when A=1, B=0, C=0 - provides discrete channel selection in 8-channel demux configurations. |
| 4 (Y2) | Active-low decoded output | Asserted LOW when A=0, B=1, C=0 - supports modular address space partitioning in FPGA/CPLD glue logic. |
| 5 (Y3) | Active-low decoded output | Asserted LOW when A=1, B=1, C=0 - enables selective activation of up to eight peripherals from three address bits. |
| 6 (Y4) | Active-low decoded output | Asserted LOW when A=0, B=0, C=1 - used in memory bank selection where C acts as MSB of block address. |
| 7 (Y5) | Active-low decoded output | Asserted LOW when A=1, B=0, C=1 - supports interleaved memory mapping in 8-bit microprocessor systems. |
| 8 (GND) | Ground reference | Primary return path for all internal logic and output currents - must be low-impedance and decoupled near VCC pin. |
| 9 (Y6) | Active-low decoded output | Asserted LOW when A=0, B=1, C=1 - facilitates compact I/O expansion in industrial HMI controllers. |
| 10 (Y7) | Active-low decoded output | Asserted LOW when A=1, B=1, C=1 - final output for full 3-bit address space coverage in 8-device select schemes. |
| 11 (C) | Binary address input | MSB of 3-bit select code - determines upper/lower half of output group when combined with B and A. |
| 12 (B) | Binary address input | Middle bit of select code - pairs with C and A to uniquely define one of eight output states per enable condition. |
| 13 (A) | Binary address input | LSB of select code - toggles between adjacent outputs (e.g., Y0/Y1 or Y4/Y5) for fine-grained peripheral addressing. |
| 14 (G1) | Active-high enable input | Must be HIGH to activate decoding - used as primary global enable or data input in demultiplexing mode. |
| 15 (G2B) | Active-low enable input | Second active-low enable - paired with G2A to form dual-enable gating, reducing need for external NAND logic. |
| 16 (VCC) | Positive supply | +5 V power rail - requires local 0.1-µF ceramic bypass capacitor placed within 5 mm of pin for noise suppression. |
Key Features
| Feature | Design Value |
|---|---|
| Three enable inputs (G1, G2A, G2B) | Enables 24-line decoding without external inverters and 32-line decoding with only one inverter - reduces PCB area and component count in multi-chip select systems. |
| TTL-compatible input thresholds | Accepts standard 74LS/74F logic levels directly - eliminates level-shifter ICs in mixed-logic-family designs. |
| Low ICC (80 µA max) | Minimizes standby power in battery-backed or energy-sensitive control modules where decode logic remains powered continuously. |
| 17 ns tpd at 5.5 V | Supports tight timing budgets in high-speed memory subsystems - ensures address decode completes before memory access window closes. |
| ±4-mA output drive | Drives LSTTL loads directly - avoids buffer stages in legacy industrial backplanes and test equipment signal routing. |
Applications
| Memory Address Decoding | Peripheral Device Selection |
|---|---|
|
Use Scenario: Selecting one of eight SRAM or EPROM chips in a microcontroller-based data logger with 64 KB address space. IC Role / Device Role / Timing Role: Acts as address-space partitioner, asserting individual chip-select (CS) lines based on upper address bits A15–A13. Use Value: Eliminates manual gating logic; 17 ns tpd ensures CS assertion aligns with memory access timing, preventing bus contention. |
Use Scenario: Enabling specific sensors (temperature, pressure, humidity) in an environmental monitoring node. IC Role / Device Role / Timing Role: Functions as digital multiplexer controller, routing MCU GPIO commands to one sensor interface at a time. Use Value: Reduces required MCU GPIO count from eight to three plus enable lines, simplifying firmware and PCB layout. |
| Logic-Level Signal Routing | Industrial I/O Expansion |
|
Use Scenario: Directing UART, SPI, or I²C signals to one of eight test points on a production line fixture. IC Role / Device Role / Timing Role: Serves as bidirectional demultiplexer, using G1 as data input and Y0–Y7 as routed output channels. Use Value: Enables single-port serial diagnostics across multiple DUTs without protocol translation or additional transceivers. |
Use Scenario: Expanding discrete input/output capability in a programmable logic controller (PLC) base unit. IC Role / Device Role / Timing Role: Decodes PLC scan-cycle address bus to assert enable signals for eight isolated relay driver ICs. Use Value: Provides deterministic, glitch-free enable sequencing - critical for safety-rated output staging in industrial automation. |
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 |
|---|---|---|---|
| SN74HC138N | CMOS version: wider VCC range (2–6 V), higher ICC (≤160 µA), slower tpd (29 ns typ at 6 V). | Suitable for mixed-voltage systems (e.g., 3.3-V MCU with 5-V peripherals) but not drop-in for strict 5-V TTL timing budgets. | Choose SN74HC138N only if supply flexibility or lower drive strength suffices; verify timing margins in target clock domain. |
| 74LS138N | Legacy bipolar TTL: 4.75–5.25 V range, higher ICC (≈36 mA), faster tpd (≈15 ns), no 5.5-V tolerance. | Compatible with vintage 74LS systems but incompatible with modern 5.5-V tolerant designs and consumes >400× more quiescent power. | Select 74LS138N solely for legacy board repair or LS-family-only environments; avoid in new designs due to power and voltage limitations. |
Compared with SN74HC138N and 74LS138N, the SN74HCT138NE4 uniquely balances TTL input compatibility, 5-V robustness, low static power, and sub-20-ns speed - making it the optimal choice for industrial 5-V logic upgrades and memory decode in cost-sensitive embedded systems.
Availability
SN74HCT138NE4 is available at Aetrix Electronics and suitable for industrial control panels, embedded memory expansion modules, and logic-level signal routing applications requiring stable component supply and long-term manufacturability.
Supply support for SN74HCT138NE4 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 industrial, automotive, and communications markets.
The SN74HCT138NE4 belongs to TI's HCT (High-Speed CMOS TTL-compatible) logic family, engineered specifically for seamless replacement of 74LS devices in 5-V systems while delivering CMOS power efficiency and noise immunity.
FAQ
What is the maximum supply voltage rating for SN74HCT138NE4?
The absolute maximum supply voltage for SN74HCT138NE4 is 7 V, but the recommended operating range is strictly 4.5 V to 5.5 V. Operating above 5.5 V risks violating recommended conditions and may degrade reliability or cause parametric drift. All specifications - including tpd, VOH, and VOL - are guaranteed only within the 4.5–5.5 V window. The SN74HCT138NE4 must never be operated continuously at 7 V.
Can SN74HCT138NE4 drive standard 74LS inputs directly?
Yes, SN74HCT138NE4 can drive standard 74LS inputs directly. Its ±4-mA output drive meets the 74LS input current requirements (IIH = 20 µA, IIL = –0.4 mA), and its VOH ≥ 3.7 V and VOL ≤ 0.33 V at 4-mA load satisfy 74LS VIH (2.0 V) and VIL (0.8 V) thresholds. This makes SN74HCT138NE4 a true TTL-compatible replacement in legacy 74LS-based systems.
How does the enable logic work on SN74HCT138NE4?
SN74HCT138NE4 requires all three enables to be simultaneously asserted: G1 must be HIGH, and both G2A and G2B must be LOW. Only then will the A/B/C inputs determine which of Y0–Y7 goes LOW. If any enable is inactive, all outputs remain HIGH. This triple-enable structure allows flexible cascading - for example, using G1 as a system-wide master enable and G2A/G2B as sub-system selects - without external logic gates.
Is SN74HCT138NE4 suitable for demultiplexing applications?
Yes, SN74HCT138NE4 functions as a 1-to-8 demultiplexer when G1 is used as the data input and A/B/C as select lines. With G2A and G2B held LOW, the data applied to G1 appears inverted on the selected Y output (e.g., G1 = HIGH → selected Y = LOW). This mode is explicitly supported in TI's datasheet and enables serial-to-parallel conversion in test fixtures, sensor arrays, and diagnostic hardware using only one IC.
What is the thermal resistance (RθJA) of SN74HCT138NE4 in PDIP package?
The junction-to-ambient thermal resistance (RθJA) for SN74HCT138NE4 in the 16-pin PDIP (N) package is 67°C/W, as specified in the Thermal Information table of the official TI datasheet. This value assumes standard JEDEC 2S2P test board conditions. For reliable operation at maximum ambient temperature (85°C), power dissipation should remain below ~150 mW to limit junction temperature to <150°C - well within the device's absolute maximum rating.
SN74HCT138NE4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74HCT
- Package/Case:
- 16-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Active
- Type:
- Decoder/Demultiplexer
- Circuit:
- 1 x 3:8
- Independent Circuits:
- 1
- Current - Output High, Low:
- 4mA, 4mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- -40°C ~ 85°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 16-PDIP
SN74HCT138NE4 FAQ
1.How can I place an order for SN74HCT138NE4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74HCT138NE4 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 SN74HCT138NE4 reliable?
The price and inventory of SN74HCT138NE4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74HCT138NE4 is usually 5 days.
3.What payment methods are accepted for SN74HCT138NE4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74HCT138NE4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74HCT138NE4?
SN74HCT138NE4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74HCT138NE4 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 SN74HCT138NE4?
For technical support, including SN74HCT138NE4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74HCT138NE4 requirements.
6.How does Aetrix verify that SN74HCT138NE4 is sourced from the original manufacturer or authorized distributors?
All SN74HCT138NE4 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 SN74HCT138NE4 meets industry standards.
7.What is the process for return or replacement of SN74HCT138NE4?
All SN74HCT138NE4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74HCT138NE4, 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 SN74HCT138NE4 part is unused and in its original packaging.
Return procedure for SN74HCT138NE4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
SN74HCT138NE4 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…
