Nexperia USA Inc. 74HCT138PW,112

Overview

74HCT138PW,112 from Nexperia is a 3-to-8 line inverting decoder/demultiplexer with TTL-compatible inputs, operating from 4.5 V to 5.5 V, featuring three active-LOW enable inputs (E1, E2), one active-HIGH enable input (E3), and eight mutually exclusive active-LOW outputs (Y0–Y7); used for memory chip select decoding and address demultiplexing in industrial microcontroller systems.

For engineers reviewing the 74HCT138PW,112 datasheet, 74HCT138PW,112 pinout, 74HCT138PW,112 application, or 74HCT138PW,112 equivalent, key selection criteria include enable logic configuration (E1/E2 LOW + E3 HIGH), propagation delay at 5 V (19–53 ns), output drive capability (±4 mA), TSSOP16 package thermal profile, and compatibility with 5 V TTL logic families.

Technical Context

The device implements a binary-to-octal decoding function where A0–A2 select exactly one of eight outputs, all driven LOW while all others remain HIGH-enabling direct connection to active-LOW chip select lines. Its triple-enable architecture supports cascading: four units plus one inverter expand to 1-of-32 decoding without external logic.

Input clamping diodes allow safe interfacing to voltages exceeding VCC when current-limiting resistors are used. The 74HCT variant guarantees TTL-level input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V at VCC = 5 V) and delivers CMOS-level output swing (VOH ≥ 3.98 V, VOL ≤ 0.26 V at IO = ±4 mA).

Key Specifications

Pinout & Package

TSSOP16 plastic thin shrink small outline package (SOT403-1), 16-pin, body width 4.4 mm, 0.65 mm pitch, exposed pad not electrically connected.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HC138PW,118, the 74HCT138PW,112 offers guaranteed TTL input compatibility at 5 V but sacrifices supply voltage flexibility; versus SN74LS138N, it delivers lower power, tighter timing control, and broader temperature support-making it preferable for new industrial designs.

Availability

74HCT138PW,112 is available at Aetrix Electronics and suitable for memory decoding, peripheral selection, demultiplexed control routing, and LED digit enable applications requiring stable component supply across industrial temperature ranges.

Supply support for 74HCT138PW,112 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

Nexperia is a global semiconductor expert delivering high-performance, reliable components for automotive, industrial, mobile, and computing markets, with leadership in logic, MOSFETs, and ESD protection.

The 74HCT138 belongs to Nexperia's high-speed TTL-compatible logic family, designed specifically for robust 5 V system interfacing where noise immunity, precise enable control, and industrial-grade reliability are critical.

FAQ

What is the maximum clock frequency supported by the 74HCT138PW,112?

The 74HCT138PW,112 is not a clocked device-it has no internal clock and operates combinatorially. Its usable switching rate is governed by propagation delay (19–53 ns at 5 V) and transition time (<22 ns). In practice, it reliably supports address decode cycles up to ~10 MHz in synchronous bus systems when paired with appropriate setup/hold timing margins.

Can the 74HCT138PW,112 drive LEDs directly?

Yes-each output can sink or source up to ±4 mA at VCC = 5 V with VOL ≤ 0.26 V and VOH ≥ 3.98 V. This supports direct driving of low-current indicator LEDs (e.g., 2 mA @ 1.8 V forward voltage) with a series resistor. For higher-current LEDs or multiplexed displays, verify total package power dissipation (max 500 mW, derated above 91 °C) and thermal layout.

How does the enable logic work when cascading multiple 74HCT138PW,112 devices?

To cascade four units into a 5-to-32 decoder, tie A0–A2 together across all devices, connect E1/E2 of each to decoded high-order bits (e.g., A3,A4), and drive E3 of each with the inverted output of a fifth 74HCT138 configured as a 2-to-4 decoder. Only one device activates per 5-bit address, ensuring mutually exclusive outputs across all 32 lines.

Is the exposed pad on the TSSOP16 package electrically connected?

No-the thermal pad on the SOT403-1 (TSSOP16) package is not electrically connected. Per Nexperia documentation, there is no electrical or mechanical requirement to solder it. If soldered, the land must remain floating or be connected to GND; it serves only thermal relief and does not affect logic functionality or pinout.