Texas Instruments SN74AHC138PWRG4

Overview

SN74AHC138PWRG4 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in a 16-pin TSSOP package, operating from 2 V to 5.5 V, with propagation delays as low as 5.7 ns at 5 V and ±8 mA output drive capability. It features three enable inputs (two active-low, one active-high) for cascading and demultiplexing in high-speed memory systems.

For engineers reviewing the SN74AHC138PWRG4 datasheet, SN74AHC138PWRG4 pinout, SN74AHC138PWRG4 application, or SN74AHC138PWRG4 equivalent, key selection criteria include VCC range compatibility, enable-input logic configuration, propagation delay vs. load capacitance, output current capability, and TSSOP thermal performance (RθJA = 135.9°C/W).

Technical Context

The SN74AHC138PWRG4 implements positive-logic binary decoding with three address inputs (A0–A2) and three independent enables (G1, G2A, G2B), where only one of eight active-low outputs (Y0–Y7) is asserted per valid input combination. Its enable architecture allows direct 24-line expansion without external inverters and supports data routing via G1 as a demultiplexer control line.

Designed for high-speed memory decoding, it delivers sub-10 ns propagation delays at 3.3 V (CL = 15 pF) and maintains rail-to-rail output swing across its full 2–5.5 V supply range. Input thresholds scale with VCC (VIH = 0.7×VCC, VIL = 0.3×VCC), ensuring robust noise immunity in mixed-voltage systems.

Key Specifications

Pinout & Package

TSSOP-16 (PW) package: 5.0 mm × 6.4 mm body size, 1.2 mm max height, lead pitch 0.65 mm, exposed thermal pad not present (non-VQFN). RoHS-compliant, NIPDAU/SN lead finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LV138APWR and 74HC138PW,118, the SN74AHC138PWRG4 offers the fastest propagation (5.7 ns), lowest static current (40 μA), and VCC-scaled input thresholds-making it optimal for high-speed, mixed-voltage, and low-power decode paths where timing margin is constrained.

Availability

SN74AHC138PWRG4 is available at Aetrix Electronics and suitable for high-speed memory decoding, peripheral selection logic, LED matrix scanning, and data demultiplexing requiring stable component supply and industrial temperature support (−40°C to +85°C).

Supply support for SN74AHC138PWRG4 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 delivering analog, embedded processing, and logic solutions with emphasis on reliability, precision, and energy efficiency.

The SN74AHC138PWRG4 belongs to TI's advanced high-speed CMOS (AHC) logic family, engineered for minimal propagation delay and broad supply voltage operation in memory and data-routing subsystems.

FAQ

What is the maximum operating frequency supported by the SN74AHC138PWRG4?

The SN74AHC138PWRG4 does not specify a maximum clock frequency because it is a combinational logic device-not a clocked sequential circuit. Its usable switching rate depends on propagation delay and system-level timing margins. With a 5.7 ns max tPD at 5 V, it supports address decode cycles up to approximately 175 MHz in ideal conditions, though real-world limits are set by board layout, load capacitance, and setup/hold timing of connected devices. The SN74AHC138PWRG4 datasheet defines performance via switching characteristics, not frequency ratings.

Can the SN74AHC138PWRG4 operate reliably at 2.5 V supply voltage?

Yes, the SN74AHC138PWRG4 is fully specified from 2 V to 5.5 V, including 2.5 V operation. At 2.5 V, VIH is guaranteed ≥1.5 V and VIL ≤0.5 V, providing 1.0 V noise margin. Propagation delay increases to 13 ns (max) at CL = 15 pF, and output drive drops to ±50 μA, which remains sufficient for driving CMOS inputs. All DC and AC parameters in the SN74AHC138PWRG4 datasheet are validated across this full range.

How should unused enable inputs be handled on the SN74AHC138PWRG4?

All unused enable inputs on the SN74AHC138PWRG4 must be held at valid logic levels to prevent undefined output states. G1 (active-high) should be tied to VCC if unused; G2A and G2B (active-low) must each be tied to GND if not used in the design. Floating enables cause indeterminate output behavior and increased ICC due to internal input stage contention. This requirement is explicitly stated in the SN74AHC138PWRG4 datasheet Section 4.2 and TI application report SCBA004.

Does the SN74AHC138PWRG4 have built-in ESD protection, and what levels are certified?

Yes, the SN74AHC138PWRG4 includes on-die ESD protection rated per JESD22: 2000 V Human-Body Model (HBM) and 1000 V Charged-Device Model (CDM). These values exceed standard industrial requirements (IEC 61000-4-2 Level 2) and eliminate the need for external TVS diodes in typical PCB handling and assembly environments. The protection circuitry is integrated into all I/O pins and is verified during TI's production test flow for every SN74AHC138PWRG4 unit.

Is the SN74AHC138PWRG4 pin-compatible with older 74LS138 or 74HC138 devices?

The SN74AHC138PWRG4 shares identical pinout and function table with 74HC138 and 74LS138 in TSSOP-16 (PW) packaging, making it a direct PCB drop-in replacement. However, electrical differences exist: SN74AHC138PWRG4 uses CMOS input thresholds (VCC-scaled), delivers faster switching (5.7 ns vs. 24 ns for HC), and draws lower ICC. While no layout change is needed, verify that downstream loads accept its rail-to-rail output swing and that timing budgets accommodate its reduced delay. The SN74AHC138PWRG4 datasheet confirms functional and mechanical compatibility with HC/LS families in PW package.