STMicroelectronics 74ACT138TTR

Overview

74ACT138TTR from STMicroelectronics is an advanced high-speed CMOS 3-to-8 line decoder with inverting outputs, designed for address decoding in memory systems and logic selection in digital control circuits. It operates from 4.5V to 5.5V, delivers 5ns typical propagation delay (t_PD), supports ±24mA symmetrical output drive, and features three enable inputs (G1, G2A, G2B) for cascading. Used in industrial microcontroller bus interfaces requiring TTL-compatible input thresholds and 50Ω transmission-line driving.

For engineers reviewing the 74ACT138TTR datasheet, 74ACT138TTR pinout, 74ACT138TTR application, or 74ACT138TTR equivalent, key selection criteria include guaranteed 5ns propagation delay at 5V, 24mA output sink/source capability, ESD-hardened 2kV inputs, and TSSOP-16 package compatibility with high-density PCB layouts.

Technical Context

The 74ACT138TTR implements a fully decoded 3-bit binary input (A, B, C) to eight active-low outputs (Y0–Y7), with combinational logic gated by three independent enables: G1 (active-high), G2A and G2B (both active-low). All enable conditions must be satisfied for decoding - G1 = HIGH and G2A = G2B = LOW - otherwise all outputs remain HIGH.

Its sub-micron C2MOS process ensures balanced t_PLH/t_PHL delays (≤10.5ns over temperature), symmetrical output impedance (|I_OH| = I_OL ≥24mA), and 4µA max quiescent ICC at 25°C. Input thresholds (VIH ≥2.0V, VIL ≤0.8V at VCC = 4.5–5.5V) guarantee robust interfacing with TTL, NMOS, and CMOS families.

Key Specifications

Pinout & Package

TSSOP-16 package: 4.4mm × 5.0mm body, 0.65mm pitch, 1.1mm height, lead-free and RoHS-compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ACT138DR and 74LCX138MTCX, the 74ACT138TTR uniquely combines TSSOP-16 miniaturization, full 5V operation, TTL-compatible thresholds, and identical enable architecture - making it optimal for legacy 5V industrial upgrades requiring footprint retention.

Availability

74ACT138TTR is available at Aetrix Electronics and suitable for memory address decoding, industrial PLC I/O expansion, automotive body control modules, and test equipment signal routing requiring stable component supply and long-term lifecycle support.

Supply support for 74ACT138TTR 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, designing and manufacturing analog, digital, and mixed-signal ICs for industrial, automotive, and consumer markets.

The 74ACT logic family targets high-speed, low-power 5V digital systems requiring TTL compatibility and robust noise immunity - optimized for industrial control, instrumentation, and legacy system upgrades.

FAQ

Is the 74ACT138TTR pin-compatible with standard 74LS138 devices?

Yes - it uses identical pinout and logic function (3-to-8 inverting decoder with three enables), but features CMOS input thresholds (VIH ≥2.0V, VIL ≤0.8V) and higher output drive (24mA vs. 8mA for LS), allowing direct replacement in most 5V TTL systems without redesign.

What is the maximum operating temperature range for continuous operation?

The 74ACT138TTR is rated for continuous operation from –55°C to +125°C ambient temperature, validated per STMicroelectronics' recommended operating conditions and DC/AC electrical specifications across this full range.

Does the device require external pull-up resistors on outputs?

No - outputs are actively driven HIGH (IOH ≥24mA) and LOW (IOL ≥24mA); pull-ups are unnecessary unless open-drain emulation or wired-OR logic is specifically required in the application.

Can G2A and G2B be tied together and driven by a single control signal?

Yes - G2A and G2B are logically OR'd internally (both must be LOW to enable), so connecting them to the same net simplifies enable control; however, doing so reduces flexibility for cascaded decoder architectures where independent gating is needed.