Toshiba Semiconductor and Storage 74HC138D

Overview

74HC138D from Toshiba is a high-speed CMOS 3-to-8 line decoder in SOIC16 package, implementing active-low decoded outputs (Y0–Y7) controlled by three binary address inputs (A, B, C) and three enable inputs (G1, G2A, G2B). It operates across 2.0–6.0 V supply, delivers 16 ns typical propagation delay at 5 V, and draws ≤4.0 µA quiescent current at 25 °C - enabling low-power memory address decoding and I/O selection in industrial control and embedded logic systems.

For engineers reviewing the 74HC138D datasheet, 74HC138D pinout, 74HC138D application, or 74HC138D equivalent, this device serves as a standard TTL-compatible decoder with cascading enables, balanced tPLH/tPHL timing, and robust ESD protection - critical for reliable address demultiplexing in multi-chip microcontroller systems and programmable logic interfaces.

Technical Context

The 74HC138D implements combinational logic decoding using silicon gate C2MOS technology, achieving LSTTL-equivalent speed while maintaining CMOS power efficiency. Its three enable inputs (G1, G2A, G2B) support hierarchical cascade connection - G1 active-high and G2A/G2B active-low - allowing direct use as a 1-of-8 selector in multi-level memory decoding trees.

All eight outputs are active-low and mutually exclusive when enabled; no output asserts unless all enables satisfy G1 = HIGH, G2A = LOW, G2B = LOW. Input thresholds meet HC-family compatibility: VIH ≥ 3.15 V (at VCC = 4.5 V), VIL ≤ 1.35 V, ensuring noise-immune interfacing with 5 V microcontrollers and FPGA I/O banks.

Key Specifications

Pinout & Package

74HC138D is housed in a 16-pin Small Outline Integrated Circuit (SOIC16) package, 7.5 mm wide, with 1.27 mm pitch and surface-mount gull-wing leads. Pin 1 is marked with a notch or dot; the package is RoHS-compliant and rated for reflow soldering per JEDEC J-STD-020.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC138N and 74HCT138D, the 74HC138D offers optimal balance of surface-mount reliability, sub-µA quiescent draw, and industrial temperature support - making it preferred for volume production of compact, energy-efficient embedded controllers where PCB space and power budget are constrained.

Availability

74HC138D is available at Aetrix Electronics and suitable for memory address decoding, peripheral selection logic, LED segment multiplexing, and interrupt prioritization requiring stable component supply across industrial temperature ranges and long-term production cycles.

Supply support for 74HC138D 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

Toshiba Electronic Devices & Storage Corporation designs and manufactures high-reliability semiconductor components for industrial, automotive, and consumer applications, with emphasis on logic, power, and memory ICs.

The 74HC138D belongs to Toshiba's HC-series high-speed CMOS logic family, engineered for drop-in replacement of LSTTL in cost-sensitive, low-power embedded systems requiring robust noise immunity and wide supply tolerance.

FAQ

What is the maximum operating temperature for the 74HC138D?

The 74HC138D is rated for continuous operation from -40 °C to +125 °C. At the upper limit, its maximum propagation delay increases to 45 ns (A/B/C → Y, VCC = 4.5 V, CL = 50 pF), and quiescent supply current rises to 160 µA - values confirmed in Toshiba's Rev. 3.0 datasheet Section 12.7. This makes the 74HC138D suitable for under-hood automotive modules and industrial motor drives where ambient heat exceeds 85 °C.

Does the 74HC138D support 3.3 V logic systems?

Yes, the 74HC138D supports 3.3 V operation with guaranteed functionality: VIH(min) = 2.31 V and VIL(max) = 0.99 V at VCC = 3.3 V (derived from proportional thresholds in Section 12.1), and output drive meets 3.3 V LVTTL requirements (VOH ≥ 3.1 V at IOL = 4 mA). The 74HC138D maintains 16 ns typical delay at 3.3 V, enabling direct interface with ARM Cortex-M microcontrollers and FPGA I/O banks without level translation.

How are the enable inputs configured for cascading multiple 74HC138D devices?

To cascade two 74HC138D decoders, tie G2A and G2B of the second device to G1 of the first, and connect the first device's Y7 output to G1 of the second. This configures the first 74HC138D as a higher-order selector: when Y7 is LOW (A=B=C=1), the second 74HC138D activates, decoding additional address bits. All three enables (G1, G2A, G2B) must simultaneously satisfy G1=HIGH and G2A=G2B=LOW for any 74HC138D to assert outputs - a feature explicitly documented in Section 2 of the Toshiba datasheet.

What is the output drive capability of the 74HC138D at 5 V supply?

At VCC = 5 V, the 74HC138D delivers IOH = -4.0 mA (high-level source) and IOL = 4.0 mA (low-level sink) while maintaining VOH ≥ 4.4 V and VOL ≤ 0.26 V - verified in Section 12.1 DC Characteristics. This allows the 74HC138D to directly drive up to four 74HC-series inputs or a single LED (with series resistor) without buffer stages, supporting fan-out-4 logic distribution in compact control panels.

Is the 74HC138D pin-compatible with other manufacturers' 74HC138 variants?

Yes, the 74HC138D adheres to JEDEC MS-012 SOIC16 mechanical dimensions and standard 74HC138 logic pinout - confirmed by Toshiba's Package Dimensions drawing and truth table in Sections 4 and 8. Pin-for-pin compatibility is maintained with NXP, ON Semiconductor, and Diodes Inc. 74HC138 offerings in SOIC16, including identical G1/G2A/G2B enable polarity, A/B/C input order, and Y0–Y7 output sequence - enabling seamless second-source substitution in production.