Diodes Incorporated 74AHCT138S16-13

Overview

74AHCT138S16-13 from Diodes Incorporated is a 3-to-8 line decoder/demultiplexer in SO-16 package, designed for pin compatibility with 74LS138. It accepts three binary address inputs (A0–A2), features three enable inputs (E1, E2 active-low; E3 active-high), and delivers eight active-low outputs (Y0–Y7) with propagation delay as low as 4.3 ns at VCC = 4.5V. Used in memory chip select decoding and peripheral demultiplexing.

For engineers reviewing the 74AHCT138S16-13 datasheet, 74AHCT138S16-13 pinout, 74AHCT138S16-13 application, or 74AHCT138S16-13 equivalent, this device supports high-speed TTL-compatible logic interfacing, operates across industrial temperature range (−40°C to +125°C), and provides Schmitt-trigger inputs for noise immunity in noisy digital control environments.

Technical Context

The 74AHCT138S16-13 implements a combinational logic decoder with three-stage enable gating: E1 and E2 must be low while E3 must be high for output activation. Its internal architecture ensures only one output goes low per valid address/enable combination, with all outputs high during disable.

It uses advanced CMOS process to achieve TTL-level input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V) while maintaining low static current (ICC ≤ 40 µA over temperature) and robust ESD protection (2 kV HBM, 1 kV CDM). Input clamp diodes allow safe operation with inputs up to 6.0 V independent of VCC.

Key Specifications

Pinout & Package

74AHCT138S16-13 is housed in a 16-pin SOIC (Small Outline Integrated Circuit) package with 1.27 mm pitch, 10.0 mm × 4.0 mm body, and gull-wing leads suitable for reflow soldering. Pin 1 is marked by a notch or dot; pin numbering follows standard SO-16 convention.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74AHCT138DR and 74VHC138M, the 74AHCT138S16-13 offers the lowest propagation delay in its class and integrated Schmitt-trigger inputs-critical for reliable operation in industrial control panels where EMI is present and signal integrity cannot be guaranteed by layout alone.

Availability

74AHCT138S16-13 is available at Aetrix Electronics and suitable for memory chip select decoding, peripheral demultiplexing, and single-line peripheral control requiring stable component supply across automotive, industrial automation, and embedded computing programs.

Supply support for 74AHCT138S16-13 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

Diodes Incorporated is a global manufacturer of discrete semiconductors and analog ICs, headquartered in Plano, Texas, with design centers across Asia and manufacturing in China, Taiwan, and the U.S.

The 74AHCT logic family targets high-speed, low-power, TTL-compatible interface applications in industrial, computing, and communications equipment where reliability and pin compatibility with legacy 74LS are essential.

FAQ

What is the maximum clock frequency supported by the 74AHCT138S16-13?

The 74AHCT138S16-13 is a combinational logic device with no internal clock; its usable frequency depends on propagation delay and system timing margins. With tPD ≤ 10.4 ns (max, CL = 15 pF), it supports address decoding in systems with bus cycles ≥ 20 ns - effectively enabling reliable operation up to 50 MHz in synchronous memory interfaces when combined with appropriate setup/hold timing.

Can the 74AHCT138S16-13 operate at 3.3 V supply?

No - the 74AHCT138S16-13 requires VCC between 4.5 V and 5.5 V per its recommended operating conditions. Operation below 4.5 V violates specification and may cause undefined output states or increased propagation delay. For 3.3 V systems, consider the 74LVC138 or 74AHC138, which are specified down to 2.0 V or 3.0 V respectively.

Are the Y0–Y7 outputs truly open-drain?

No - the outputs are push-pull CMOS, capable of actively driving both high and low. Each output can source up to 0.1 V below VCC at IOH = −50 µA and sink up to 0.36 V at IOL = 8 mA. They are not open-drain and do not require external pull-up resistors for standard logic interfacing.

How does the enable logic work across E1, E2, and E3?

E1 and E2 are active-low enables; E3 is active-high. The decoder activates only when E1 = LOW, E2 = LOW, and E3 = HIGH. Any deviation - such as E1 = HIGH or E3 = LOW - forces all Y0–Y7 outputs HIGH regardless of A0–A2 values. This three-input enable scheme enables hierarchical cascading without external logic gates.