Texas Instruments SN74AHC138PWRE4

Overview

SN74AHC138PWRE4 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in 16-pin TSSOP (PW) package, operating from 2 V to 5.5 V, with propagation delays as low as 5.7 ns at 5 V and 15 pF load, designed for high-speed memory decoding and data-routing systems where minimal system delay is critical.

For engineers reviewing the SN74AHC138PWRE4 datasheet, SN74AHC138PWRE4 pinout, SN74AHC138PWRE4 application, or SN74AHC138PWRE4 equivalent, this page delivers verified functional behavior, real-world timing constraints, cascading enable logic implementation guidance, and validated alternative options for memory address decoding and demux signal routing.

Technical Context

The SN74AHC138PWRE4 implements active-high binary address selection (A0–A2) combined with three independent enable inputs: one active-high (G1) and two active-low (G2A, G2B), enabling flexible hierarchical decoding without external inverters. Its positive-logic function table supports both decoder and demultiplexer modes, with any enable input usable as a data channel.

It uses advanced AHC CMOS technology delivering rail-to-rail output swing, low static current (≤40 μA at 5.5 V), and robust ESD protection (2000 V HBM, 1000 V CDM). Latch-up immunity exceeds 250 mA per JESD17, supporting reliable operation in noisy industrial and embedded control environments.

Key Specifications

Pinout & Package

SN74AHC138PWRE4 is housed in a 16-pin TSSOP (PW) package measuring 5.00 mm × 4.40 mm body size, with 0.65 mm lead pitch and exposed thermal pad (not electrically connected; may be grounded or left floating).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LV138APWR and 74HC138D,653, the SN74AHC138PWRE4 uniquely balances 5.7 ns speed, 2–5.5 V flexibility, and 2000 V HBM robustness-making it the optimal choice for new industrial controllers and high-reliability embedded memory systems.

Availability

SN74AHC138PWRE4 is available at Aetrix Electronics and suitable for memory address decoding, FPGA I/O expansion, industrial bus arbitration, and test equipment signal routing requiring stable component supply and long-term production continuity.

Supply support for SN74AHC138PWRE4 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

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and logic solutions with over 90 years of innovation in high-reliability IC design.

The SN74AHC138PWRE4 belongs to TI's AHC logic family, engineered for high-speed, low-power decoding in memory subsystems and data-path routing where propagation delay and noise immunity are critical.

FAQ

What is the maximum operating frequency supported by SN74AHC138PWRE4?

The SN74AHC138PWRE4 does not specify a clock frequency since it is a combinational logic device. Its usable switching rate is determined by propagation delay (5.7 ns max at 5 V) and load capacitance. For a 15 pF load, it reliably supports input transition rates up to ~100 MHz in burst-mode operation, provided setup/hold times are met and VCC remains stable within 2–5.5 V.

Can SN74AHC138PWRE4 be used as a demultiplexer, and how is that configured?

Yes, SN74AHC138PWRE4 functions as a 1-to-8 demultiplexer when one enable input (typically G1) serves as the data input while A0–A2 act as select lines. With G2A and G2B held low, asserting G1 high routes the logic state to the selected Yx output (active-low), making SN74AHC138PWRE4 ideal for serial-to-parallel data distribution in control logic.

Does SN74AHC138PWRE4 require external pull-up resistors on its outputs?

Yes, SN74AHC138PWRE4 outputs are active-low and do not include internal pull-ups. External pull-up resistors (typically 1–10 kΩ to VCC) are required to establish defined high states on Y0–Y7 when deselected. This configuration enables wired-OR bus structures and compatibility with TTL or mixed-voltage loads.

What is the thermal resistance (RθJA) of the SN74AHC138PWRE4 in its TSSOP package?

The SN74AHC138PWRE4 in the PW (TSSOP-16) package has a junction-to-ambient thermal resistance (RθJA) of 135.9 °C/W, as specified in TI's SCLS258N datasheet. This value assumes standard JEDEC 2-layer board conditions; adding a copper pour under the thermal pad reduces RθJA significantly, improving sustained output current capability.

How does the enable logic of SN74AHC138PWRE4 simplify cascading with multiple devices?

SN74AHC138PWRE4 uses three enables-G1 (active-high), G2A (active-low), and G2B (active-low with internal inversion)-to enable direct 24-line decoding without external inverters. For example, connecting G2B of a second SN74AHC138PWRE4 to Y0 of the first allows seamless expansion, as G2B's inversion eliminates the need for discrete inverter logic between stages.