Texas Instruments CD74AC238PWR

Overview

CD74AC238PWR from Texas Instruments is a 3-line to 8-line decoder/demultiplexer IC designed for high-speed memory decoding and data-routing applications. It operates across 1.5 V to 5.5 V, delivers ±24 mA output drive, features three enable inputs (G1, G2A, G2B), and achieves propagation delays as low as 3.8 ns at 5 V - enabling use in fast-access memory systems and address decoding for microcontrollers and FPGAs.

For engineers reviewing the CD74AC238PWR datasheet, CD74AC238PWR pinout, CD74AC238PWR application, or CD74AC238PWR equivalent, this device supports cascaded decoding schemes up to 32 lines, offers ESD immunity exceeding 2 kV (HBM), and provides balanced tPLH/tPHL timing critical for synchronous bus interfaces and demultiplexed control signal distribution.

Technical Context

The CD74AC238PWR implements active-high and active-low enable logic (G1 high-active; G2A/G2B low-active) to simplify hierarchical decoding without external inverters. Its CMOS architecture ensures SCR-latchup resistance and rail-to-rail output swing under load.

Propagation delay varies with supply voltage: 15 ns max at 5 V, 19.1 ns at 3.3 V, and 170 ns at 1.5 V (all over –40°C to +85°C), with matched tPLH/tPHL ensuring minimal skew across all eight outputs (Y0–Y7).

Key Specifications

Pinout & Package

TSSOP-16 (PW) package: 5.00 mm × 6.4 mm body size, 1.2 mm max height, lead pitch 0.65 mm, exposed pad optional (not electrically connected in PW variant).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74AC138PWR and 74LVC138PW,118, the CD74AC238PWR uniquely supports 1.5 V operation and retains full performance down to –55°C, making it the only option among the three qualified for extended-temperature aerospace or military subsystems.

Availability

CD74AC238PWR is available at Aetrix Electronics and suitable for industrial control panels, automotive body electronics, and test instrumentation requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74AC238PWR 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 connectivity technologies, with over 50 years of innovation in high-reliability logic and interface solutions.

The CD74AC238PWR belongs to TI's Advanced CMOS (AC) logic family, engineered for high-speed, low-power decoding in mission-critical memory and data-path systems - emphasizing timing precision, voltage flexibility, and robustness in harsh environments.

FAQ

What is the maximum clock frequency supported by CD74AC238PWR in demultiplexer mode?

The CD74AC238PWR does not operate on a clock signal - it is combinational logic. Its effective maximum switching rate is determined by propagation delay: at 5 V, worst-case tPD is 15 ns, supporting input address changes up to ~66 MHz in sustained operation. For reliable timing closure, design margins should limit transitions to ≤40 MHz in systems with trace routing delays or capacitive loading.

Can CD74AC238PWR drive LEDs directly without current-limiting resistors?

No. While CD74AC238PWR provides ±24 mA output drive, its absolute maximum continuous output current is ±50 mA per pin - but sustained LED driving requires external current-limiting resistors to prevent thermal overstress and ensure output voltage compliance. For example, driving a 2 V red LED at 10 mA from 5 V requires a 300 Ω resistor; omitting it risks exceeding safe junction temperature.

Does CD74AC238PWR require pull-up or pull-down resistors on unused enable inputs?

Yes. Per TI's SCBA004 guidance, all unused inputs - including G1, G2A, and G2B - must be tied to a defined logic level. G1 should connect to VCC (to enable), while G2A and G2B must connect to GND (since they are active-low). Floating enables cause undefined output states and increased ICC current, potentially leading to functional failure or excessive power draw.

Is CD74AC238PWR pin-compatible with CD74HC238PWR?

No. Although both are 3-to-8 decoders in TSSOP-16, CD74AC238PWR uses AC-series CMOS with 1.5–5.5 V operation and ±24 mA drive, whereas CD74HC238PWR is HC-series with 2–6 V range and only ±4 mA drive. Their enable logic is identical, but AC's lower input thresholds and higher drive make them non-interchangeable without circuit revalidation.

What is the thermal pad requirement for CD74AC238PWR in the PW package?

The CD74AC238PWR in TSSOP (PW) package does not include a thermal pad - unlike the WQFN (BQB) variant. Its thermal performance relies solely on leads and PCB copper; RθJA is 126.2°C/W. No soldering of an exposed pad is required or possible. Layout should maximize copper area under the package body and use ≥2 oz copper for heatsinking if operating near 125°C ambient.