Nexperia USA Inc. 74AHCT138BQ,115

Overview

74AHCT138BQ,115 from Nexperia is a 3-to-8 line inverting decoder/demultiplexer in DHVQFN16 package, operating at 4.5–5.5 V with TTL-compatible inputs, 13.5 ns max propagation delay (CL = 50 pF), and -40 °C to +125 °C temperature range. It enables memory chip select decoding and parallel expansion to 1-of-32 decoding via cascaded enable logic.

For engineers reviewing the 74AHCT138BQ,115 datasheet, 74AHCT138BQ,115 pinout, 74AHCT138BQ,115 application, or 74AHCT138BQ,115 equivalent, key selection criteria include TTL-level input compatibility, active-LOW/active-HIGH enable configuration, output drive capability (8 mA sink), thermal-enhanced QFN packaging, and guaranteed operation across industrial and extended temperature ranges.

Technical Context

The device implements combinational logic decoding with three binary address inputs (A0–A2) and eight mutually exclusive active-LOW outputs (Y0–Y7). Selection requires simultaneous assertion of two active-LOW enables (E1, E2) and one active-HIGH enable (E3), enabling precise hierarchical control in multi-chip systems.

Its architecture supports dual functional modes: as a decoder for address-based chip selection, or as an 8-output demultiplexer when one enable input serves as data path and others as strobes - all without external logic. Input Schmitt-trigger action ensures noise immunity on address and enable lines.

Key Specifications

Pinout & Package

DHVQFN16 (SOT763-1) package: 2.5 × 3.5 × 0.85 mm body, no leads, thermally enhanced exposed pad (non-soldered by default), 16 terminals in quad arrangement with terminal 1 index area marked.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS138N, 74AHCT138BQ,115 delivers 46% faster propagation, 99.7% lower quiescent current, and extended temperature support - critical for battery-powered and thermally constrained applications. Versus 74AHC138BQ,115, it trades CMOS input thresholds for guaranteed TTL interoperability, simplifying mixed-logic-system integration.

Availability

74AHCT138BQ,115 is available at Aetrix Electronics and suitable for memory chip select decoding, microcontroller peripheral expansion, industrial I/O multiplexing, and automotive body control modules requiring stable component supply across extended temperature ranges.

Supply support for 74AHCT138BQ,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 delivering high-performance, reliable, and energy-efficient logic, analog, and discrete components for automotive, industrial, and consumer applications.

The 74AHCT series targets industrial and automotive systems requiring TTL-compatible CMOS logic with extended temperature operation, low power, and high noise immunity - optimized for robust digital control and interface functions.

FAQ

What is the maximum clock frequency supported by 74AHCT138BQ,115?

The 74AHCT138BQ,115 is a combinational logic device with no internal clock; its operational speed is defined by propagation delay. With a maximum tpd of 13.5 ns (E1/E2→Yn, CL = 50 pF, VCC = 5 V), it supports address/data switching rates up to approximately 74 MHz in worst-case cascaded configurations - limited by system-level setup/hold timing, not device clocking.

Can 74AHCT138BQ,115 operate at 3.3 V supply?

No - the 74AHCT138BQ,115 is specified only for 4.5 V to 5.5 V operation per its recommended conditions table. At 3.3 V, VIH minimum (2.0 V) may be met, but VOH and VOL parameters are not guaranteed, and internal gate thresholds become unreliable. For 3.3 V systems, use the 74AHC138BQ,115 variant instead.

Is the exposed thermal pad on the DHVQFN16 package required to be soldered?

No - the exposed pad (terminal 1) has no electrical function and requires no solder connection. If soldered, it must remain floating or be tied to GND; doing so improves thermal performance by up to 15 °C/W but is optional. PCB land pattern should follow Nexperia's SOT763-1 layout guidelines to avoid solder voiding.

How does the enable logic prevent partial output activation?

All eight outputs remain HIGH unless all three enables are simultaneously asserted: E1 = LOW, E2 = LOW, and E3 = HIGH. This triple-condition requirement ensures no output goes LOW during power-up, reset, or enable signal skew - eliminating spurious chip selects or demux glitches that could corrupt memory or peripheral states.