Texas Instruments CD74HC138MTG4

Overview

CD74HC138MTG4 from Texas Instruments is a high-speed CMOS 3-to-8 line decoder/demultiplexer with active-low outputs, operating from 2 V to 6 V, featuring 13 ns typical propagation delay at 5 V/15 pF, -55°C to +125°C temperature range, and three enable inputs (G2, G1, G0) for cascading in memory address decoding and I/O port selection applications.

For engineers reviewing the CD74HC138MTG4 datasheet, CD74HC138MTG4 pinout, CD74HC138MTG4 application, or CD74HC138MTG4 equivalent, key selection criteria include its inverting output logic, wide supply voltage tolerance, industrial-grade thermal range, LSTTL-compatible fanout, and SOIC-16 package compatibility with standard PCB footprints.

Technical Context

The CD74HC138MTG4 implements a silicon-gate CMOS 3:8 decoder with three address inputs (A0–A2) and three strobe enables (G2, G1, G0), where any active strobe forces all eight outputs (Y0–Y7) high. Its function table defines strict low-active output behavior only when all enables are asserted and a valid 3-bit address is applied.

It uses standard CMOS input thresholds (VIH = 3.15 V min, VIL = 1.35 V max at VCC = 4.5 V), delivers VOH ≥ 3.98 V and VOL ≤ 0.33 V at 4 mA load, and exhibits balanced transition times (tt = 15 ns typ) and low dynamic power dissipation (Cpd = 67 pF).

Key Specifications

Pinout & Package

CD74HC138MTG4 is housed in a 16-pin SOIC (D) package measuring 9.90 mm × 3.90 mm, with standard JEDEC MS-012AC footprint and gull-wing leads compatible with automated SMT assembly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC138DR and MC74HC138ADTR2G, CD74HC138MTG4 offers identical decode functionality and SOIC-16 mechanical compatibility but carries TI's legacy industrial qualification and specific marking (HC138M), making it preferred for long-lifecycle legacy system maintenance.

Availability

CD74HC138MTG4 is available at Aetrix Electronics and suitable for memory address decoding, I/O port selection, LED multiplexing, and test equipment signal routing requiring stable component supply across extended temperature ranges and long-term industrial program support.

Supply support for CD74HC138MTG4 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 ICs, with over 90 years of innovation in industrial, automotive, and aerospace electronics.

CD74HC138MTG4 belongs to TI's CD74HC high-speed CMOS logic family, designed specifically for reliable, low-power address decoding and signal routing in harsh-environment industrial control and instrumentation systems.

FAQ

What is the maximum clock frequency supported by CD74HC138MTG4 for address decoding?

The CD74HC138MTG4 does not operate on a clock; it is a combinational logic device. Its usable switching rate is determined by propagation delay (13 ns typical) and output transition time (15 ns typical), supporting reliable operation in systems with address bus toggle rates up to approximately 30 MHz under loaded conditions (CL = 15 pF). For CD74HC138MTG4, timing margins must be verified against specific board trace capacitance and load conditions.

Can CD74HC138MTG4 drive LEDs directly without external transistors?

Yes, CD74HC138MTG4 can directly sink up to 4 mA per output (Y0–Y7) at VCC = 4.5 V with VOL ≤ 0.33 V, sufficient for low-current indicator LEDs with appropriate series resistors. For CD74HC138MTG4, this capability eliminates external drivers in multiplexed display applications, though total package current must remain within ±25 mA per output and ±50 mA for VCC/GND pins.

Does CD74HC138MTG4 support 3.3 V microcontroller interfaces?

Yes, CD74HC138MTG4 operates from 2 V to 6 V and features CMOS-compatible input thresholds - at VCC = 3.3 V, VIH = 2.31 V (min) and VIL = 0.99 V (max) - ensuring reliable recognition of 3.3 V logic levels. For CD74HC138MTG4, no level-shifting circuitry is required when interfacing with standard 3.3 V microcontrollers.

How are the enable inputs G0, G1, and G2 used in cascaded configurations?

In cascading, G2 (active-high) serves as the primary enable, while G1 and G0 (both active-low) provide secondary gating. For example, two CD74HC138MTG4 devices can decode 4-bit addresses: the most significant bit selects which device is enabled via G2, while A2–A0 select the output within that device. All three enables must be satisfied for any output to activate - a design feature confirmed in the CD74HC138MTG4 function table.

Is CD74HC138MTG4 pin-compatible with CD74HCT138 variants?

No - although CD74HC138MTG4 and CD74HCT138 share identical pinout and package, they differ electrically: CD74HC138MTG4 uses CMOS input thresholds (VIH = 70% VCC), while CD74HCT138 uses TTL-compatible thresholds (VIH = 2.0 V min). Interchanging them may cause logic misreads in mixed-voltage systems; CD74HC138MTG4 must be used where CMOS-level compatibility is required.