Texas Instruments SN74AHC238PWR

Overview

SN74AHC238PWR from Texas Instruments is a 3-to-8-line noninverting decoder/demultiplexer with three active-low strobes (G₀, G₁) and one active-high strobe (G₂), operating from 2V to 5.5V V_CC, delivering ≤10.5ns propagation delay at 5V/50pF, and supporting industrial temperature range (–40°C to 125°C). It enables memory device selection on shared data buses by decoding 3-bit address inputs (A₀–A₂) into eight independent chip-select outputs (Y₀–Y₇).

For engineers reviewing the SN74AHC238PWR datasheet, SN74AHC238PWR pinout, SN74AHC238PWR application, or SN74AHC238PWR equivalent, key selection considerations include strobe input logic polarity (G₀/G₁ low-active, G₂ high-active), output drive capability (±8mA at 5V), CMOS input compatibility, TSSOP-16 package thermal performance (R_θJA = 135.9°C/W), and functional behavior under cascaded enable conditions.

Technical Context

The SN74AHC238PWR implements a positive-logic 3:8 decoder with three independent enable paths: G₂ (active-high), G₁ (active-low), and G₀ (active-low). All outputs are forced low when any strobe is asserted - enabling hierarchical decoding and demultiplexing via strobe-as-data routing. Its balanced CMOS push-pull outputs provide symmetrical sourcing/sinking (±8mA at 5V), while standard CMOS inputs require fast transitions (<20ns/V at 5V) to prevent oscillation.

Functional operation follows a strict priority: outputs remain low unless all three strobes are simultaneously inactive (G₂ = HIGH, G₁ = LOW, G₀ = LOW), after which only the Y_n corresponding to the binary value of A₂A₁A₀ goes HIGH. The device exhibits no internal latching - output state updates synchronously with input changes, with propagation delays varying by strobe path (e.g., t_PHL = 5.4ns for G₁→Y at 5V/15pF).

Key Specifications

Pinout & Package

TSSOP-16 (PW) package: 5mm × 6.4mm body, 0.65mm lead pitch, exposed thermal pad not present (unlike WQFN variant). Pin 1 marked by beveled corner; pins numbered counterclockwise.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LV238APWR and 74HC238PW,118, the SN74AHC238PWR uniquely balances wide voltage operation (2V–5.5V), industrial temperature support, low quiescent current, and sub-11ns speed - making it the only option qualified for high-reliability 5V embedded control with tight timing budgets.

Availability

SN74AHC238PWR is available at Aetrix Electronics and suitable for memory subsystem design, industrial I/O expansion, and automotive body-control modules requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SN74AHC238PWR 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 50 years of innovation in high-reliability interface and signal-path components.

The SN74AHC238PWR belongs to TI's AHC logic family - designed specifically for low-power, high-speed translation between mixed-voltage domains in industrial automation, automotive electronics, and communications infrastructure.

FAQ

What is the maximum capacitive load the SN74AHC238PWR can drive while maintaining specified timing?

The SN74AHC238PWR is characterized up to 50pF load capacitance - all switching specifications (e.g., 10.5ns max t_PD) are guaranteed at this value. Driving larger loads increases propagation delay nonlinearly and may cause signal integrity issues; TI recommends limiting total trace + input capacitance to ≤50pF for full spec compliance. For heavier loads, buffer stages or series termination should be added.

How do the strobe inputs G₀, G₁, and G₂ interact in the SN74AHC238PWR?

In the SN74AHC238PWR, all outputs Y₀–Y₇ go LOW if *any* strobe is asserted: G₀ = LOW, G₁ = LOW, or G₂ = HIGH. Only when G₀ = HIGH, G₁ = HIGH, and G₂ = LOW does decoding occur - then Y_n follows A₂A₁A₀. This OR-like enable structure allows flexible hierarchical control, such as using G₂ as a master enable and G₀/G₁ as subordinate interlocks.

Can unused inputs on the SN74AHC238PWR be left floating?

No - unused inputs on the SN74AHC238PWR must never be left floating. CMOS inputs have high impedance and undefined voltage states when unconnected, causing excessive current draw, logic instability, or oscillation. TI mandates termination to V_CC or GND; a 10kΩ pull-up/down resistor is recommended if dynamic control is needed later. Floating A₀–A₂ or strobes will corrupt output behavior.

Does the SN74AHC238PWR support hot insertion or live insertion into a powered system?

The SN74AHC238PWR is not hot-insertion rated. Its absolute maximum ratings specify V_CC must be applied before inputs - applying input signals before V_CC risks exceeding VI limits (–0.5V to 7V) and activating clamp diodes, potentially damaging the device. Always sequence V_CC prior to signal application in backplane or modular systems.

What is the thermal performance difference between SN74AHC238PWR and its WQFN variant SN74AHC238BQBR?

The SN74AHC238PWR (TSSOP-16) has R_θJA = 135.9°C/W, while SN74AHC238BQBR (WQFN-16) achieves 105.6°C/W due to its exposed thermal pad. Under identical 5V/8mA load conditions, the TSSOP version runs ~30°C hotter at ambient - making the WQFN preferred for thermally constrained layouts, though both meet industrial temp specs. No thermal pad is present on SN74AHC238PWR.