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Home > Products > Integrated Circuits (ICs) > Logic > Signal Switches, Multiplexers, Decoders

STMicroelectronics 74AC138TTR

Name: 74AC138TTR
Brand: STMicroelectronics
SKU: 74AC138TTR
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: 74AC138TTR

Manufacturer:: STMicroelectronics

Category:: Signal Switches, Multiplexers, Decoders

Package:: 16-TSSOP (0.173", 4.40mm Width)

Datasheet:: 74AC138TTR.pdf

Description:: IC DECODER/DEMUX 1X3:8 16TSSOP

Quantity:: RFQ Add To RFQ list

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Inventory:1,348

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Product details

Overview

74AC138TTR from STMicroelectronics is an advanced high-speed CMOS 3-to-8 line decoder with inverting outputs, designed for memory address decoding and data routing in digital systems. It features propagation delay of 4.5 ns (typ.) at 5 V, symmetrical output drive (±24 mA), operating voltage range of 2–6 V, and three enable inputs (G1, G2A, G2B) supporting cascaded decoder configurations. Used in industrial control logic and microprocessor peripheral interfacing.

For engineers reviewing the 74AC138TTR datasheet, 74AC138TTR pinout, 74AC138TTR application, or 74AC138TTR equivalent, key selection criteria include propagation delay matching, 50 Ω transmission line drive capability, ESD immunity (2 kV), latch-up robustness, and TSSOP-16 footprint compatibility with legacy 74-series layouts.

Technical Context

The 74AC138TTR implements a fully decoded 3-bit binary input (A, B, C) to eight active-low outputs (Y0–Y7), with three independent enable inputs enabling hierarchical addressing. Its sub-micron C2MOS process ensures low ICC (4 µA max) and high noise immunity (VIH/VIL = 28% VCC min).

All outputs exhibit balanced tPLH ≅ tPHL propagation delays and symmetrical impedance (|IOH| = IOL ≥ 24 mA), supporting clean signal integrity on 50 Ω transmission lines. Input rise/fall time specification (8 ns/V) enforces controlled edge rates to minimize ringing in high-speed bus environments.

Key Specifications

Parameter	Value and Actual Design Meaning
tPD (typ)	4.5 ns at VCC = 5 V - enables ≤220 MHz address decode timing in synchronous memory systems
VCC Range	2 V to 6 V - supports mixed-voltage board designs including 3.3 V and 5 V logic domains
IOL / IOH	24 mA min - drives standard TTL loads and 50 Ω transmission lines without external buffers
VNIH / VNIL	28% VCC min - provides robust noise margin against crosstalk in dense PCB layouts
ICC (max)	4 µA at TA = 25°C - enables ultra-low static power in battery-backed or standby logic circuits
ESD Rating	2 kV HBM - protects against handling damage during manual assembly and rework
Operating Temp	−55°C to +125°C - qualified for extended industrial and automotive under-hood applications

Pinout & Package

TSSOP-16 package: 4.9 × 6.4 mm body, 0.65 mm pitch, 16-pin surface-mount with exposed pad not present; RoHS-compliant, moisture sensitivity level MSL3.

Pin/Terminal	Circuit Role	Design Meaning
1, 2, 3	A, B, C	Binary address select inputs - determine active-low output Y0–Y7 per truth table
4, 5	G2A, G2B	Active-high enable inputs - both must be low for decode function to activate
6	G1	Active-low enable input - must be high for decode function to activate
7, 9–15	Y0–Y7	Inverting decoded outputs - only one low at a time when enabled and address valid
8	GND	Ground reference - return path for all internal logic and output current
16	VCC	Positive supply - powers internal gates and output drivers; bypassing required near pin

Key Features

Feature	Design Value
Propagation delay balance	tPLH ≅ tPHL ensures minimal skew between rising/falling edges on same output
Cascade-ready enables	G1 (active-low), G2A/G2B (active-high) allow direct chaining of multiple 74AC138s for 4-to-16 or larger decoding
50 Ω line driving	Guaranteed performance into 50 Ω loads eliminates need for external series termination resistors
Input hysteresis margin	VNIH/VNIL = 28% VCC minimizes false triggering from slow-rising or noisy address signals
Latch-up immunity	Enhanced C2MOS process prevents destructive latch-up under transient overvoltage conditions

Applications

Memory Address Decoding

Microcontroller Peripheral Selection

Use Scenario: Selecting one of eight RAM/ROM chips in a 64 KB memory map using A15–A13 address bits.

IC Role / Device Role / Timing Role: 3-to-8 inverting decoder generating chip-select signals synchronized to address bus transitions.

Use Value: 4.5 ns typical propagation delay ensures setup/hold compliance with 25 ns SRAM access cycles.

Use Scenario: Routing UART, SPI, or GPIO peripherals to a single microcontroller bus with shared control lines.

IC Role / Device Role / Timing Role: Address-space demultiplexer enabling one peripheral at a time via decoded CSn signals.

Use Value: Balanced tPLH/tPHL and 24 mA drive support reliable peripheral enable timing across temperature extremes.

Industrial PLC I/O Expansion

Digital Test Equipment Signal Routing

Use Scenario: Expanding discrete input/output points in programmable logic controllers using modular backplane addressing.

IC Role / Device Role / Timing Role: Cascaded decoder providing 1-of-8 selection for isolated I/O module slots.

Use Value: −55°C to +125°C rating and 2 kV ESD immunity ensure reliability in electrically noisy factory environments.

Use Scenario: Switching test signals between DUT pins and measurement instruments in automated test fixtures.

IC Role / Device Role / Timing Role: High-speed signal path selector with deterministic enable timing and low-glitch behavior.

Use Value: 50 Ω transmission line drive capability maintains signal fidelity up to 100 MHz test frequencies.

Equivalent & Alternatives

The following parts are listed as comparable options for similar 3-to-8 inverting decoder applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
SN74AC138PWR	Same AC specs; slightly higher ICC (8 µA max); SOIC-16 vs TSSOP-16	Requires PCB redesign for SOIC footprint; less suitable for high-density layouts	Prefer when legacy SOIC assembly infrastructure exists and thermal dissipation is non-critical
74LVC138AD,118	Lower VCC range (1.65–3.6 V); 3.3 V optimized; 5.5 ns tPD (typ); 24 mA drive retained	Not 5 V tolerant; incompatible with mixed 5 V/3.3 V systems unless level-shifted	Prefer for pure 3.3 V embedded systems where lower dynamic power and smaller die size are prioritized

Compared with SN74AC138PWR and 74LVC138AD,118, the 74AC138TTR uniquely supports full 2–6 V operation with 5 V bus compatibility, TSSOP-16 space savings, and guaranteed 50 Ω line drive-making it optimal for industrial upgrades requiring pin-compatible 74-series replacement with enhanced speed and noise margin.

Availability

74AC138TTR is available at Aetrix Electronics and suitable for memory subsystem design, microcontroller peripheral interface, industrial I/O expansion, and automated test equipment requiring stable component supply across extended temperature ranges.

Supply support for 74AC138TTR 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, specializing in automotive, industrial, and power management ICs with strong analog and digital portfolio depth.

The 74AC138 belongs to ST's legacy high-speed CMOS logic family, engineered for drop-in replacement of 74LS/74F devices while delivering superior speed, noise immunity, and power efficiency in industrial control and computing infrastructure.

FAQ

Is the 74AC138TTR compatible with 5 V TTL logic levels?

Yes. The 74AC138TTR accepts TTL-compatible input thresholds (VIH ≥ 2.1 V, VIL ≤ 0.9 V at VCC = 3.0 V; VIH ≥ 3.15 V, VIL ≤ 1.35 V at VCC = 4.5 V) and delivers VOH ≥ 4.4 V and VOL ≤ 0.5 V at 24 mA load under 5 V operation-fully interoperable with standard 5 V TTL and CMOS families.

Can the 74AC138TTR drive multiple 74AC inputs directly?

Yes. With an output drive strength of ±24 mA and input leakage < ±1 µA, a single 74AC138TTR output can fan out to at least 10 standard 74AC inputs while maintaining specified VOH/VOL margins and propagation delay, assuming proper PCB layout and decoupling.

What is the maximum clock frequency supported for address decoding?

The device does not operate on a clock; it is combinatorial. However, with 4.5 ns typical propagation delay and balanced tPLH/tPHL, it supports reliable decoding of address transitions up to approximately 220 MHz (based on 1/(2 × tPD)), provided input slew rates meet the 8 ns/V requirement and load capacitance remains ≤50 pF.

Does the TSSOP-16 package require special soldering profile considerations?

Yes. As an MSL3 component, the 74AC138TTR requires pre-bake if exposed to ambient >30°C/60% RH for >168 hours, and reflow must follow JEDEC J-STD-020 profile with peak temperature ≤260°C, ramp rate ≤3°C/s, and time above 217°C limited to 60–150 seconds to prevent delamination or voiding.

74AC138TTR Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: 74AC

Package/Case:: 16-TSSOP (0.173", 4.40mm Width)

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

Type:: Decoder/Demultiplexer

Circuit:: 1 x 3:8

Independent Circuits:: 1

Current - Output High, Low:: 24mA, 24mA

Voltage Supply Source:: Single Supply

Voltage - Supply:: 2V ~ 6V

Operating Temperature:: -55°C ~ 125°C

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 16-TSSOP

74AC138TTR FAQ

1.How can I place an order for 74AC138TTR through Aetrix?

Please submit a Request for Quotation (RFQ) for 74AC138TTR 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 74AC138TTR reliable?

The price and inventory of 74AC138TTR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 74AC138TTR is usually 5 days.

3.What payment methods are accepted for 74AC138TTR?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 74AC138TTR transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for 74AC138TTR?

74AC138TTR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your 74AC138TTR 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 74AC138TTR?

For technical support, including 74AC138TTR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 74AC138TTR requirements.

6.How does Aetrix verify that 74AC138TTR is sourced from the original manufacturer or authorized distributors?

All 74AC138TTR 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 74AC138TTR meets industry standards.

7.What is the process for return or replacement of 74AC138TTR?

All 74AC138TTR units undergo pre-shipment inspection (PSI). If there is an issue with 74AC138TTR, 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 74AC138TTR part is unused and in its original packaging.

Return procedure for 74AC138TTR:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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