Texas Instruments CD74HC238NS

Overview

CD74HC238NS from Texas Instruments is a high-speed CMOS 3-to-8 line decoder/demultiplexer with noninverting outputs, operating from 2 V to 6 V, featuring 13 ns typical propagation delay at 5 V/15 pF, -55°C to +125°C temperature range, and three enable inputs (E1̅, E2̅, E3) for cascading in memory address decoding or data-routing systems.

For engineers reviewing the CD74HC238NS datasheet, CD74HC238NS pinout, CD74HC238NS application, or CD74HC238NS equivalent, this page delivers verified functional behavior, SOP-16 package details, truth table–confirmed output polarity, thermal performance (θ_JA = 64°C/W), and direct alternatives for industrial control, instrumentation, and logic-level signal routing designs.

Technical Context

The CD74HC238NS implements a binary-decoded 3-input (A0–A2) to 8-output logic function where all eight outputs are active-high - unlike the inverting CD74HC138 - and are enabled only when E1̅ = LOW, E2̅ = LOW, and E3 = HIGH. Its HC-family silicon-gate CMOS process ensures rail-to-rail output swing and low static current (≤160 µA over full temperature range).

Propagation delay is tightly specified across voltage (2–6 V) and load (15–50 pF); transition times remain balanced (t_TLH/t_THL ≤19 ns at 4.5 V/50 pF), and fanout supports up to 10 LSTTL loads. Input thresholds meet 30% noise immunity (NIL/NIL = 30% of V_CC) at 5 V, confirming robust operation in noisy embedded environments.

Key Specifications

Pinout & Package

SOP-16 (Small Outline Package, NS suffix), 16-pin surface-mount, 3.9 mm body width, 1.2 mm max height, JEDEC MO-153 compliant, θ_JA = 64°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC138M and SN74LV138APWR, the CD74HC238NS uniquely delivers noninverting outputs across the full -55°C to +125°C range with 2–6 V flexibility - making it irreplaceable in legacy 5 V industrial controllers and new designs requiring guaranteed active-HIGH assertion without added components.

Availability

CD74HC238NS is available at Aetrix Electronics and suitable for industrial control systems, test equipment signal routing, automotive body electronics, and memory-mapped peripheral interfacing requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HC238NS 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 for industrial, automotive, and communications markets.

The CD74HC238NS belongs to TI's legacy HC logic family - engineered for high noise immunity, wide supply tolerance, and seamless drop-in replacement of obsolete TTL decoders in reliability-critical systems.

FAQ

What is the output behavior of CD74HC238NS versus CD74HC138?

The CD74HC238NS features noninverting outputs: Y0–Y7 go HIGH for the selected address (e.g., A2A1A0 = 000 → Y0 = HIGH). In contrast, CD74HC138 outputs are inverting: the same address yields Y0 = LOW. This fundamental polarity difference means CD74HC238NS directly drives active-HIGH loads like LED anodes or chip-select inputs without external inverters, while CD74HC138 requires them for equivalent functionality. Both share identical pinout, enable structure, and timing specs.

Can CD74HC238NS operate at 3.3 V and remain fully specified?

Yes, CD74HC238NS is fully specified from 2 V to 6 V, including 3.3 V. At V_CC = 3.3 V, VIH is guaranteed ≥ 2.31 V and VIL ≤ 1.1 V (30% noise margin), propagation delay is ≤38 ns (CL = 50 pF), and output drive remains ±25 mA. All DC and AC parameters in the datasheet apply across this full range - no derating required for 3.3 V operation in commercial or industrial designs.

What is the maximum clock/data frequency supported by CD74HC238NS?

CD74HC238NS is a combinational logic device with no internal clock; its speed is governed by propagation delay and transition time. With t_PD = 13 ns (typ) and t_TLH/t_THL ≤19 ns (at 5 V/50 pF), it reliably handles address/data toggle rates up to ~20 MHz in worst-case scenarios. For clean 10 ns address setup/hold windows, sustained 25 MHz operation is achievable in controlled impedance layouts with proper decoupling - confirmed by TI's switching specifications across -55°C to +125°C.

Is CD74HC238NS pin-compatible with any HCT-series decoders?

Yes, CD74HC238NS is pin-compatible with CD74HCT238 variants (e.g., CD74HCT238M, CD74HCT238PW) in the same package - same SOP-16 footprint, identical pin functions, and matching enable/address/output assignments. However, HCT versions require 4.5–5.5 V supply and offer TTL-input compatibility (VIH ≥ 2 V, VIL ≤ 0.8 V), whereas CD74HC238NS supports 2–6 V and CMOS input thresholds. Electrical substitution is possible only if supply and input logic families match.

Does CD74HC238NS require external pull-up or pull-down resistors on unused inputs?

No, CD74HC238NS has no internal input biasing; all inputs (A0–A2, E1̅, E2̅, E3) must be actively driven to valid logic levels. Floating inputs risk increased ICC, erratic outputs, or latch-up. Unused address inputs should be tied to GND or V_CC; unused enables must be held inactive (E1̅ = HIGH, E2̅ = HIGH, E3 = LOW) to prevent unintended output activation. TI explicitly cautions against floating inputs in the datasheet's handling notes.