My Inquiry
My Account
Texas Instruments SN74AHC138D
- Part No.:
- SN74AHC138D
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74AHC138D.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,175
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
SN74AHC138D 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 (VCC = 5 V, CL = 15 pF), ±25 mA output drive, and three independent enable inputs (two active-low, one active-high) for cascading in memory decoding systems.
For engineers reviewing the SN74AHC138D datasheet, SN74AHC138D pinout, SN74AHC138D application, or SN74AHC138D equivalent, this device is selected for high-speed address decoding in microcontroller peripherals, FPGA I/O expansion, and legacy bus demultiplexing where low propagation delay, rail-to-rail logic compatibility, and deterministic enable-controlled output gating are required.
Technical Context
The SN74AHC138D implements positive-logic binary decoding with three address inputs (A0–A2) and three enables (G1, G2A, G2B), where only one of eight active-low outputs (Y0–Y7) goes low when all enables are asserted per function table. Its architecture supports direct demultiplexing by using an enable input as data path control.
It uses advanced CMOS AHC technology delivering high noise immunity (VIH/VIL thresholds scale with VCC), latch-up immunity >250 mA (JESD 17), and ESD robustness (2000 V HBM, 1000 V CDM), making it suitable for industrial control backplanes and mixed-voltage system interfaces.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 2 V to 5.5 V - supports interoperability across 3.3 V and 5 V logic domains without level shifters |
| tPLH / tPHL (5 V, 15 pF) | 5.7 ns max - enables sub-100 MHz address decode timing in SRAM/ROM systems |
| Output Drive (IOL/IOH) | ±8 mA at 5 V - sufficient to directly drive multiple 74AHC inputs or small LED loads |
| Input Thresholds (VCC = 5 V) | VIH = 3.85 V, VIL = 1.65 V - provides >1.3 V noise margin under worst-case VCC tolerance |
| Power Dissipation Capacitance | 13 pF - predicts dynamic power consumption ≤ 0.33 mW/MHz at 5 V, critical for low-power decoding |
| Operating Temperature | −40 °C to +85 °C - qualified for commercial and industrial ambient environments |
| ESD Rating (HBM) | 2000 V - exceeds JEDEC JESD22-A114 requirement, reducing board-level protection needs |
Pinout & Package
SN74AHC138D is housed in a 16-pin SOIC (D) package measuring 9.9 mm × 6.0 mm body size, with standard 1.27 mm lead pitch and 2.00 mm max height per IPC-7351 SOP outline NS0016A.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A0, A1, A2 | Binary address inputs | Select one of eight outputs via 3-bit code; high-impedance when device disabled |
| G1 | Active-high enable | Primary global enable; all outputs high unless G1 = HIGH and G2A/G2B asserted |
| G2A, G2B | Active-low enables | G2A and G2B must both be LOW to activate decoding; enables hierarchical cascading |
| Y0–Y7 | Active-low decoded outputs | Only one output is LOW per valid input combination; all others remain HIGH |
| VCC, GND | Power supply terminals | Decoupling capacitor (0.1 µF ceramic) required within 10 mm of VCC/GND pins per layout guidelines |
Key Features
| Feature | Design Value |
|---|---|
| Three enable inputs (G1, G2A, G2B) | Enables 24-line decoding without external inverters and 32-line with only one inverter |
| Propagation delay ≤5.7 ns (5 V) | Reduces effective system decode latency below typical 55 ns SRAM access time |
| Rail-to-rail input voltage range | Accepts VI from 0 to VCC, eliminating need for external biasing on unused inputs |
| Latch-up immunity >250 mA | Ensures robust operation during hot-swap or transient overvoltage events in backplane systems |
| SOIC-16 footprint compatibility | Direct drop-in replacement for legacy 74LS138/74HC138 in existing PCB layouts |
Applications
| Memory Address Decoding | FPGA I/O Expansion |
|---|---|
Use Scenario: Selecting one of eight SRAM or ROM chips in a microcontroller-based embedded system with limited address lines. IC Role / Device Role / Timing Role: 3-to-8 address decoder that gates chip-select signals based on upper address bits and control strobes. Use Value: Eliminates discrete gate logic; propagation delay <9.5 ns ensures no added wait states in 50 MHz bus cycles. |
Use Scenario: Expanding limited FPGA GPIO count to drive eight peripheral enable lines (e.g., sensors, DACs, displays). IC Role / Device Role / Timing Role: Demultiplexer converting 3-bit FPGA output into eight independent active-low enables. Use Value: Enables single-cycle enable assertion with deterministic timing, avoiding FPGA routing delays. |
| Legacy Bus Demultiplexing | Industrial Control Backplane |
Use Scenario: Routing a shared data bus to one of eight instrument modules in test equipment using ISA-like control protocol. IC Role / Device Role / Timing Role: Data-path selector controlled by bus address and /IOR or /IOW strobes. Use Value: Active-low outputs interface directly with TTL/CMOS peripherals; enable inputs synchronize with bus cycle timing. |
Use Scenario: Isolating fault conditions across eight PLC output channels using enable-controlled signal gating. IC Role / Device Role / Timing Role: Safety-critical enable distributor that asserts only one channel's driver enable at a time. Use Value: Built-in enable arbitration prevents simultaneous activation; latch-up immunity withstands field transients. |
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 |
|---|---|---|---|
| SN74HC138DR | Slower propagation delay (21 ns @ 5 V), higher ICC (80 µA max), same pinout and logic function | Lower speed margin; unsuitable for >10 MHz address buses but adequate for 8-bit MCU peripherals | Choose for cost-sensitive, non-timing-critical designs where AHC speed is unnecessary |
| 74LVC138AD,118 | 3.3 V only (1.65–3.6 V), lower VCC min, 5.5 ns delay (3.3 V), 50 mA drive, different pinout (TSSOP16) | Not compatible with 5 V systems; requires level translation if interfacing with 5 V controllers | Prefer for modern 3.3 V-only designs needing higher drive strength and tighter timing control |
Compared with SN74HC138DR and 74LVC138AD,118, the SN74AHC138D uniquely balances 5 V compatibility, sub-10 ns timing, and SOIC-16 footprint-making it the optimal choice for upgrading legacy 74LS138 systems while maintaining PCB layout continuity.
Availability
SN74AHC138D is available at Aetrix Electronics and suitable for memory decoding, FPGA I/O expansion, legacy bus demultiplexing, and industrial control backplane applications requiring stable component supply and long-term industrial temperature support.
Supply support for SN74AHC138D 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 portfolio coverage.
The SN74AHC138D belongs to TI's AHC logic family, engineered for high-speed, low-power decoding in memory and data-routing systems where propagation delay and supply voltage flexibility are critical design constraints.
FAQ
What is the maximum clock frequency supported by SN74AHC138D in demultiplexer mode?
The SN74AHC138D does not operate on a clock; it is combinational logic. Its usable switching rate is determined by propagation delay and system setup/hold timing. With tPHL/tPLH ≤9.5 ns (5 V, 15 pF), it supports reliable operation in address decode paths up to ~50 MHz bus cycles, assuming proper PCB layout and load capacitance ≤15 pF. The SN74AHC138D itself imposes no clock limit.
Can SN74AHC138D interface directly with 3.3 V microcontrollers while powered at 5 V?
No - SN74AHC138D VCC must match the logic high level of its inputs. Driving A0–A2 or enables from a 3.3 V MCU while SN74AHC138D is powered at 5 V violates VIH specification (requires ≥3.85 V at VCC = 5 V). To interface, either operate SN74AHC138D at 3.3 V (within 2–5.5 V range) or use a level translator. The SN74AHC138D datasheet confirms VIH scales with VCC.
How many SN74AHC138D devices can be cascaded to decode 5 address lines into 32 outputs?
Two SN74AHC138D devices can decode 5 address lines into 32 outputs: use A4–A2 to select one of four SN74AHC138D units (via G1/G2 enables), and A1–A0 to select among eight outputs per unit. The SN74AHC138D datasheet explicitly shows a 32-bit decoding scheme requiring only one external inverter - confirming this topology is validated and electrically supported.
Is SN74AHC138D pin-compatible with older 74LS138 in SOIC-16 package?
Yes - SN74AHC138D uses identical SOIC-16 pinout, terminal numbering, and function mapping as 74LS138 and 74HC138. All address inputs (A0–A2), enables (G1, G2A, G2B), outputs (Y0–Y7), VCC, and GND occupy matching positions. This allows direct PCB replacement without layout changes, provided timing and drive requirements are verified.
Does SN74AHC138D require pull-up or pull-down resistors on unused inputs?
Yes - all unused inputs (including enables and address lines) must be tied to VCC or GND per TI application report SCBA004. Floating inputs cause increased ICC, erratic output behavior, and potential latch-up. For SN74AHC138D, connecting unused enables to inactive state (e.g., G1 to GND, G2A/G2B to VCC) ensures predictable disable behavior and meets recommended operating conditions.
SN74AHC138D Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AHC
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Bulk
- 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
SN74AHC138D FAQ
1.How can I place an order for SN74AHC138D through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AHC138D 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 SN74AHC138D reliable?
The price and inventory of SN74AHC138D are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AHC138D is usually 5 days.
3.What payment methods are accepted for SN74AHC138D?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AHC138D transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74AHC138D?
SN74AHC138D orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AHC138D 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 SN74AHC138D?
For technical support, including SN74AHC138D datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AHC138D requirements.
6.How does Aetrix verify that SN74AHC138D is sourced from the original manufacturer or authorized distributors?
All SN74AHC138D 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 SN74AHC138D meets industry standards.
7.What is the process for return or replacement of SN74AHC138D?
All SN74AHC138D units undergo pre-shipment inspection (PSI). If there is an issue with SN74AHC138D, 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 SN74AHC138D part is unused and in its original packaging.
Return procedure for SN74AHC138D:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
SN74AHC138D 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…
