Texas Instruments SN74HC138PWRE4

Overview

SN74HC138PWRE4 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in TSSOP-16 package, operating from 2 V to 6 V, with 15 ns typical propagation delay at 6 V, ±4-mA output drive at 5 V, and active-low outputs enabling direct LED column sinking in multiplexed displays.

For engineers reviewing the SN74HC138PWRE4 datasheet, SN74HC138PWRE4 pinout, SN74HC138PWRE4 application, or SN74HC138PWRE4 equivalent, this page delivers verified functional modes, thermal metrics for TSSOP-16, enable-input cascading logic, and real-world timing behavior under 50-pF load conditions.

Technical Context

The SN74HC138PWRE4 implements combinational decoding using three binary select inputs (A, B, C) and three enable terminals (G1 high-active, G2A/G2B low-active), where all outputs remain high unless all enables are asserted and exactly one input combination is selected-yielding a single active-low output among Y0–Y7.

Its CMOS architecture ensures rail-to-rail input thresholds, 80-µA maximum ICC at 6 V, and compatibility with LSTTL loads; propagation delay varies from 38 ns (min, 6 V) to 225 ns (max, 2 V) across the full operating temperature range of –40°C to +85°C.

Key Specifications

Pinout & Package

TSSOP-16 package (5.00 mm × 4.40 mm), 0.65-mm pitch, moisture sensitivity level 1 (260°C peak reflow), RoHS-compliant NiPdAu lead finish.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC138PWRE4, SN74HCT138PWRE4 offers guaranteed TTL input compatibility at the cost of higher static current, while 74LV138PW,118 trades 5-V operation and industrial temperature range for lower power and faster 3.3-V performance.

Availability

SN74HC138PWRE4 is available at Aetrix Electronics and suitable for LED matrix drivers, memory address decoders, industrial I/O expanders, and factory automation logic controllers requiring stable component supply across automotive, industrial, and consumer production programs.

Supply support for SN74HC138PWRE4 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 ICs, with over 90 years of innovation in high-reliability, high-performance components.

The SN74HC138PWRE4 belongs to TI's HC logic family, designed for low-power, high-speed decoding in memory systems and data-routing applications where propagation delay and output drive are critical.

FAQ

What is the maximum clock frequency supported by SN74HC138PWRE4 for reliable decoding?

The SN74HC138PWRE4 is a combinational logic device-not clocked-so it has no clock input or maximum clock frequency. Its usable switching rate depends on propagation delay: at 6 V, tpd ≤38 ns (max), supporting address/data transitions up to ~26 MHz in worst-case timing paths. System-level timing must account for setup/hold at upstream registers and load capacitance.

Can SN74HC138PWRE4 drive LEDs directly without current-limiting resistors?

No. While SN74HC138PWRE4 provides ±4-mA output drive at 5 V, it cannot safely sink LED forward current without external series resistors. Each Yx output must include a resistor sized to limit current to ≤4 mA (e.g., 270 Ω for 5-V supply and 2-V LED drop). Exceeding rated output current risks parametric shift or long-term reliability degradation.

How do the three enable inputs (G1, G2A, G2B) interact in SN74HC138PWRE4 operation?

All three enables must be simultaneously active for decoding: G1 must be HIGH, and both G2A and G2B must be LOW. If any enable is violated, all eight outputs (Y0–Y7) go HIGH regardless of A/B/C state. This allows hierarchical expansion-e.g., using G1 of one device as a decoded output from another SN74HC138PWRE4 to build larger decoders.

Is SN74HC138PWRE4 compatible with 3.3-V microcontrollers driving its inputs?

Yes. At VCC = 3.3 V, SN74HC138PWRE4 guarantees VIH ≥2.31 V and VIL ≤0.99 V, matching standard 3.3-V CMOS logic levels. Input current remains ≤1 µA, placing negligible load on MCU GPIOs. No level-shifting circuitry is required for direct interface.

What thermal derating applies to SN74HC138PWRE4 in TSSOP-16 package at 85°C ambient?

For SN74HC138PWRE4 in TSSOP-16, RθJA = 141.6°C/W. At TA = 85°C and maximum ICC = 80 µA at 6 V (0.48 mW), junction temperature rise is only ~0.07°C - well within 150°C absolute max. Derating is unnecessary for normal operation; however, simultaneous switching of multiple outputs increases dynamic power and local heating.