Texas Instruments CD74HC238MT

Overview

CD74HC238MT from Texas Instruments is a high-speed CMOS 3-to-8 line decoder/demultiplexer with noninverting (active-high) outputs, 16-pin SOIC package, -55°C to +125°C operating temperature range, typical propagation delay of 13 ns at V_CC = 4.5 V and C_L = 15 pF, and 2 V to 6 V supply voltage support. It serves as an address decoder in microcontroller-based memory systems and I/O port selection circuits.

For engineers reviewing the CD74HC238MT datasheet, CD74HC238MT pinout, CD74HC238MT application, or CD74HC238MT equivalent, this page delivers verified functional mode behavior, strobe-controlled demultiplexing capability, output polarity confirmation (Y₀–Y₇ active-high), thermal performance data, and real-world substitution guidance for industrial control and instrumentation designs.

Technical Context

The CD74HC238MT implements a 3-input address decoder with three independent enable inputs (G2, G1, G0) - one standard (G2) and two active-low (G1, G0) - enabling hierarchical cascading without external logic. Its noninverting output architecture forces all eight Y₀–Y₇ outputs low when any strobe is asserted, and asserts exactly one high output per valid A2:A0 combination when enabled.

It operates across the full HC voltage range (2 V–6 V), delivers 10 LSTTL load fanout at standard outputs, and maintains balanced t_PLH/t_PHL transition times under varying capacitive loads (C_L = 15 pF to 50 pF). The device uses silicon-gate CMOS technology with input leakage ≤ ±1 µA and ICC ≤ 160 µA over temperature.

Key Specifications

Pinout & Package

CD74HC238MT is supplied in a 16-pin SOIC (D) package with 9.90 mm × 3.90 mm body size, gull-wing leads, and RoHS-compliant NiPdAu lead finish. It is rated MSL Level-1 (unlimited floor life) and compatible with standard reflow profiles.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC238MT, CD74HC138M96 requires signal inversion for active-high loads but offers drop-in PCB compatibility, while SN74HC238N provides identical logic in a through-hole package with better thermal performance but larger board area.

Availability

CD74HC238MT is available at Aetrix Electronics and suitable for industrial control systems, aerospace data acquisition modules, and automotive engine management units requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HC238MT 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 IC design and manufacturing.

The CD74HC238MT belongs to TI's HC-series high-speed CMOS logic family, engineered for low-power, wide-voltage, and extended-temperature operation in mission-critical industrial and defense systems.

FAQ

What is the output behavior of CD74HC238MT when all enable inputs are asserted?

When G₂ is high and both G₁ and G₀ are low, CD74HC238MT enables normal decoding: exactly one of Y₀–Y₇ goes high based on A2:A0, while the other seven remain low. If any enable condition fails (e.g., G₂ low or G₁/G₀ high), all eight outputs are forced low - confirming its noninverting, enable-gated architecture. This behavior is verified in Table 7-2 of the official datasheet.

Can CD74HC238MT operate reliably at 3.3 V supply voltage?

Yes, CD74HC238MT supports 2 V to 6 V operation per its recommended conditions. At V_CC = 3.3 V, it maintains full functionality: VIH ≤ 2.31 V, VIL ≥ 1.0 V, VOH ≥ 3.15 V (IOH = –20 µA), and VOL ≤ 0.33 V (IOL = 4 mA). Propagation delay increases to ~18 ns (typ), remaining well within most 3.3 V system timing budgets.

Is CD74HC238MT pin-compatible with CD74HC138M96?

Yes, CD74HC238MT and CD74HC138M96 share identical 16-pin SOIC (D) packaging, pin assignments, and DC/AC electrical specifications - including supply range, enable logic, and address input behavior. The sole functional difference is output polarity: CD74HC238MT drives Y₀–Y₇ high on selection, whereas CD74HC138M96 drives them low.

What is the maximum capacitive load CD74HC238MT can drive while maintaining specified timing?

CD74HC238MT is characterized for C_L = 15 pF (tpd = 13 ns typ at V_CC = 4.5 V) and C_L = 50 pF (tpd = 30 ns max at V_CC = 4.5 V). Driving loads >50 pF increases propagation delay nonlinearly and may cause output transition time degradation. For >50 pF loads, buffer stages or reduced slew-rate design techniques are recommended to maintain timing integrity in CD74HC238MT applications.

Does CD74HC238MT require external pull-up or pull-down resistors on unused inputs?

Yes - per TI layout guidelines (Section 9.1), all unused inputs on CD74HC238MT (e.g., unconnected address or enable lines) must be terminated to V_CC or GND to prevent floating states. Leaving inputs unconnected risks undefined output behavior, increased ICC, and potential oscillation. For CD74HC238MT, tying unused enables to inactive states (e.g., G₀/G₁ to V_CC, G₂ to GND) ensures predictable disable behavior.