Texas Instruments CD74HCT138MTE4

Overview

CD74HCT138MTE4 from Texas Instruments is a high-speed CMOS 3-to-8 line decoder/demultiplexer with active-low outputs, designed for memory address decoding and data routing in industrial control and embedded systems. It operates at 4.5–5.5 V, delivers 14 ns typical propagation delay (V_CC = 4.5 V, C_L = 15 pF), supports -55°C to +125°C temperature range, and features three enable inputs (G2, G1, G0) for cascading.

For engineers reviewing the CD74HCT138MTE4 datasheet, CD74HCT138MTE4 pinout, CD74HCT138MTE4 application, or CD74HCT138MTE4 equivalent, this page provides verified functional modes, real-world timing behavior under load, LSTTL-compatible input thresholds, and precise package-level design guidance for SOIC-16 layout and thermal management.

Technical Context

The CD74HCT138MTE4 implements a single 3:8 decoder with three address inputs (A2–A0) and three independent strobe enables (G2, G1, G0). When any strobe is asserted-G2 high or G1/G0 low-all eight outputs (Y0–Y7) are forced high; only the selected output goes low when all enables are satisfied and address matches.

Its HCT logic family ensures direct compatibility with LSTTL inputs (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V), while maintaining CMOS power efficiency (I_CC ≤ 160 µA over full temp range) and noise immunity (NIL/NIH = 30% of V_CC).

Key Specifications

Pinout & Package

CD74HCT138MTE4 is supplied in a 16-pin SOIC (D) package measuring 9.90 mm × 3.90 mm, with standard 1.27 mm pitch and gull-wing leads. Pin 1 is marked by a beveled corner or dot; pin 8 is GND, pin 16 is V_CC.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT138DR and 74ACT138SCX, the CD74HCT138MTE4 offers the broadest temperature range (-55°C to +125°C), lowest ICC (≤160 µA), and proven reliability in long-lifecycle industrial deployments-making it optimal for cost-sensitive, thermally demanding, or maintenance-critical systems.

Availability

CD74HCT138MTE4 is available at Aetrix Electronics and suitable for industrial control panels, automotive body electronics, and aerospace data acquisition systems requiring stable component supply across extended temperature ranges and multi-year production cycles.

Supply support for CD74HCT138MTE4 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 90 years of innovation in high-reliability components.

The CD74HCT138MTE4 belongs to TI's legacy high-speed CMOS logic family, engineered for robust 5 V system interfacing, memory expansion, and industrial-grade signal routing where LSTTL compatibility and wide temperature operation are essential.

FAQ

What is the maximum clock frequency supported by CD74HCT138MTE4 for reliable address decoding?

The CD74HCT138MTE4 does not operate on a clock; it is combinational logic. Its 14 ns typical propagation delay (at V_CC = 4.5 V, C_L = 15 pF) supports reliable decoding in systems with address setup/hold times ≥20 ns - sufficient for 50 MHz microcontroller buses and 25 MHz synchronous memory interfaces. Maximum usable frequency depends on system-level timing margins, not internal clocking.

Can CD74HCT138MTE4 be used to demultiplex a serial data stream?

Yes - the CD74HCT138MTE4 can function as a 1-to-8 demultiplexer by using A2–A0 as the 3-bit channel address and one strobe input (e.g., G2) as the data enable. When G2 toggles synchronously with data edges, the selected Yx output mirrors the G2 state. This configuration is widely used for routing UART TX or SPI MOSI to multiple peripherals, provided timing constraints (t_pd, t_t) are met in the target system.

Does CD74HCT138MTE4 require external pull-up resistors on its outputs?

No - the CD74HCT138MTE4 has push-pull outputs capable of actively driving both high and low logic states. Each output sources up to 4 mA (V_OH ≥ 3.7 V) and sinks up to 4 mA (V_OL ≤ 0.4 V) at V_CC = 4.5 V. Pull-ups are unnecessary unless interfacing with open-drain systems or implementing wired-OR logic, which is not standard for this device.

How does the enable logic of CD74HCT138MTE4 differ from CD74HC138?

The CD74HCT138MTE4 uses identical enable architecture to the CD74HC138: G2 is active-high, G1 and G0 are active-low. However, CD74HCT138MTE4 accepts LSTTL-compatible input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V), whereas CD74HC138 requires CMOS thresholds (V_IL ≤ 1.35 V, V_IH ≥ 3.15 V at V_CC = 4.5 V). This makes CD74HCT138MTE4 interoperable with legacy 5 V TTL without level shifters.

Is CD74HCT138MTE4 pin-compatible with CD74HCT238?

Yes - CD74HCT138MTE4 and CD74HCT238 share identical pinout, package, and enable structure. The sole functional difference is output polarity: CD74HCT138MTE4 outputs are active-low (Yx = L when selected), while CD74HCT238 outputs are active-high (Yx = H when selected). No PCB changes are required to substitute one for the other; only firmware or downstream logic must accommodate the inverted output state.