Nexperia USA Inc. 74HCT138BQ,115

Overview

74HCT138BQ,115 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) and one active-HIGH enable input (E3), eight mutually exclusive active-LOW outputs (Y0–Y7), and specified for -40 °C to +125 °C operation. It enables memory chip select decoding and parallel expansion to 1-of-32 decoding using four ICs and one inverter.

For engineers reviewing the 74HCT138BQ,115 datasheet, 74HCT138BQ,115 pinout, 74HCT138BQ,115 application, or 74HCT138BQ,115 equivalent, key selection considerations include TTL-level input compatibility, propagation delay of 20 ns (typ.) at VCC = 4.5 V and CL = 50 pF, active-LOW output polarity, DHVQFN16 thermal-enhanced packaging, and support for demultiplexing via enable-input-as-data routing.

Technical Context

The 74HCT138BQ,115 implements a combinational logic decoder with strict mutual exclusivity: only one output goes LOW when all enables are satisfied (E1 = LOW, E2 = LOW, E3 = HIGH) and address inputs A0–A2 define the selected line. Its enable architecture supports hierarchical decoding-E1/E2/E3 allow cascading without external logic inversion beyond a single inverter for 5-to-32 expansion.

Input clamping diodes permit interfacing to voltages exceeding VCC when used with current-limiting resistors. The device lacks 3-state outputs, so all eight outputs are always driven-either HIGH (inactive) or LOW (active)-with VOL ≤ 0.26 V at IO = 4.0 mA and VOH ≥ 3.98 V at IO = –4.0 mA under recommended conditions.

Key Specifications

Pinout & Package

DHVQFN16 package (SOT763-1): 2.5 mm × 3.5 mm × 0.85 mm body, no leads, thermally enhanced exposed pad (non-soldered by default), 16 terminals, pin 1 index marked on top surface.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HCT138PW,118 and SN74HCT138PWR, the 74HCT138BQ,115 offers superior thermal performance in space-constrained designs and lower high-temperature supply current-critical for sealed automotive or industrial enclosures where airflow is restricted and long-term reliability is prioritized.

Availability

74HCT138BQ,115 is available at Aetrix Electronics and suitable for memory decoding, industrial I/O expansion, automotive body control, and test equipment signal routing requiring stable component supply across extended temperature ranges and consistent lead-time visibility.

Supply support for 74HCT138BQ,115 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 focused on essential semiconductors-high-performance, reliable components for power management, logic, ESD protection, and analog applications.

The 74HCT138BQ,115 belongs to Nexperia's industry-standard logic family, designed specifically for robust, low-power decoding and demultiplexing in automotive, industrial, and computing systems demanding wide temperature operation and high noise immunity.

FAQ

What is the maximum clock frequency supported by the 74HCT138BQ,115 for address decoding?

The 74HCT138BQ,115 does not operate on a clock-it is purely combinational logic. Its usable input update rate is governed by propagation delay (20 ns typ. at VCC = 4.5 V) and input transition rate (≥83 ns/V at VCC = 6 V). For reliable operation with 10 ns address setup/hold, maximum effective toggle rate is ~10 MHz in worst-case timing paths.

Can the 74HCT138BQ,115 be used as a 1-to-8 demultiplexer, and how is data routed?

Yes: configure E3 as the data input (HIGH = logic 1, LOW = logic 0), hold E1 and E2 LOW, and use A0–A2 to select which Yx output reflects the E3 state. All unselected outputs remain HIGH; the selected output mirrors E3 inverted-so E3 = HIGH yields Yx = LOW, and E3 = LOW yields Yx = HIGH.

Is the exposed thermal pad on the DHVQFN package required to be soldered to PCB ground?

No. Per Nexperia's datasheet (SOT763-1), the exposed pad (terminal 1 index area) has no electrical or mechanical requirement to be soldered. If soldered, it must remain floating or connect to GND-never to VCC or signal nets-to avoid latch-up or thermal stress.

How does the 74HCT138BQ,115 differ from the 74HC138 variant in system integration?

The 74HCT138BQ,115 uses TTL-compatible inputs (VIH = 2.0 V, VIL = 0.8 V), enabling direct connection to 5 V microcontrollers and older logic without level shifters. The 74HC138 requires CMOS-level inputs (VIH ≈ 3.15 V at VCC = 4.5 V), making it unsuitable for mixed-voltage systems with legacy TTL sources.