Texas Instruments SN74HCT138PWRG4

Overview

SN74HCT138PWRG4 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in TSSOP-16 package, operating at 4.5–5.5 V with 17 ns typical propagation delay, ±4-mA output drive, and TTL-compatible inputs. It serves as a high-speed memory address decoder or data routing switch in embedded control and digital logic systems.

For engineers reviewing the SN74HCT138PWRG4 datasheet, SN74HCT138PWRG4 pinout, SN74HCT138PWRG4 application, or SN74HCT138PWRG4 equivalent, key selection criteria include propagation delay under 34 ns at 5.5 V, enable-input cascading capability, LSTTL load compatibility, and industrial temperature range (–40°C to +85°C) for reliable operation in memory subsystems and bus decoding.

Technical Context

The SN74HCT138PWRG4 implements active-low 3-to-8 decoding with three independent enable inputs (G1, G2A, G2B): one active-high and two active-low. This architecture enables seamless cascading of multiple devices without external inverters-e.g., a 24-line decoder requires no additional logic, while a 32-line implementation needs only one inverter.

Its TTL-compatible input thresholds (VIH = 2.0 V min, VIL = 0.8 V max) ensure direct interfacing with legacy 5-V logic families, and its low ICC (80 µA max) supports power-sensitive applications where static current budget is constrained.

Key Specifications

Pinout & Package

TSSOP-16 package: 5.00 mm × 4.40 mm body, 0.65 mm lead pitch, 1.2 mm max height, RoHS-compliant NiPdAu lead finish, MSL Level-1 (260°C peak reflow).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC138PW and 74ACT138SCX, the SN74HCT138PWRG4 uniquely balances TTL compatibility, 17-ns speed, and industrial temperature rating-making it optimal for legacy 5-V embedded systems where interoperability and timing predictability are prioritized over ultra-low power or extreme speed.

Availability

SN74HCT138PWRG4 is available at Aetrix Electronics and suitable for memory address decoding, peripheral multiplexing, interrupt vector selection, and LED matrix row driving requiring stable component supply across industrial production cycles.

Supply support for SN74HCT138PWRG4 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic ICs with broad industrial, automotive, and consumer applications.

The SN74HCT138PWRG4 belongs to TI's 74HCT logic family, designed specifically for high-speed memory decoding and data-routing systems requiring TTL-compatible inputs, low propagation delay, and robust industrial operation.

FAQ

What is the maximum propagation delay of the SN74HCT138PWRG4 at 5.5 V?

The maximum propagation delay of the SN74HCT138PWRG4 is 34 ns at VCC = 5.5 V and TA = 25°C, as specified in the Switching Characteristics table under "Enable → Any Y" condition. This value ensures compatibility with fast memory devices whose access times exceed 34 ns, preserving system-level timing margins in decoding paths.

Can the SN74HCT138PWRG4 operate with a 3.3-V supply?

No, the SN74HCT138PWRG4 is not rated for 3.3-V operation. Its recommended operating voltage range is strictly 4.5 V to 5.5 V. Applying 3.3 V may result in undefined output states, increased propagation delay, or failure to meet VIH/VIL thresholds-TI does not characterize or guarantee functionality below 4.5 V.

How many enable inputs does the SN74HCT138PWRG4 have, and what are their logic polarities?

The SN74HCT138PWRG4 has three enable inputs: G1 (active-high), G2A (active-low), and G2B (active-low). All three must be asserted simultaneously (G1 = high, G2A = low, G2B = low) for the decoder to respond to A/B/C inputs and drive Y0–Y7 outputs.

Is the SN74HCT138PWRG4 pin-compatible with other package variants of the same part number?

Yes, the SN74HCT138PWRG4 (TSSOP-16) shares identical pinout and electrical behavior with other 16-pin variants like SN74HCT138DRG4 (SOIC-16) and SN74HCT138NSR (SOP-16). Pin functions-including G1, G2A, G2B, A–C, Y0–Y7, VCC, and GND-are positionally identical across these packages, enabling drop-in replacement where board layout permits.

Does the SN74HCT138PWRG4 require external pull-up resistors on its outputs?

No, the SN74HCT138PWRG4 features push-pull outputs capable of actively driving both high and low logic levels. Its outputs can source up to 4 mA and sink up to 4 mA at 5 V, eliminating the need for external pull-ups in standard LSTTL-load applications. Pull-ups are only required if interfacing with open-drain systems or non-standard voltage domains.