Texas Instruments CD74HC42E

Overview

CD74HC42E from Texas Instruments is a high-speed CMOS BCD-to-decimal decoder IC that selects one of ten active-low outputs (Y0–Y9) based on a 4-bit binary-coded decimal input (A0–A3), operates from 2V to 6V, delivers 12ns typical propagation delay at 5V/15pF, and supports -55°C to +125°C industrial/military temperature range for reliable logic decoding in harsh environments.

For engineers reviewing the CD74HC42E datasheet, CD74HC42E pinout, CD74HC42E application, or CD74HC42E equivalent, key selection considerations include its buffered CMOS inputs/outputs, LSTTL-load drive capability (10 loads), wide VCC range, high noise immunity (NIL/NIH = 30% of VCC), and compatibility with legacy LS logic systems requiring low-power BCD decoding.

Technical Context

The CD74HC42E implements a standard 1-of-10 decoder function using silicon-gate CMOS technology, where only one output goes low per valid BCD input (0000–1001); all outputs remain high for invalid inputs (1010–1111). It features fully buffered inputs and outputs to ensure signal integrity and consistent fanout performance across temperature.

Its propagation delay (12ns typ. @ 5V/15pF) and transition times are balanced for minimal skew, while quiescent current remains low (≤160µA max over full temperature range), enabling stable operation in battery-powered or thermally constrained systems without sacrificing speed.

Key Specifications

Pinout & Package

CD74HC42E is supplied in a 16-lead plastic dual in-line package (PDIP), with 0.3-inch body width and through-hole mounting compatibility. Pin spacing follows JEDEC MS-001 standard.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar BCD-to-decimal decoding applications.

Compared with CD74HC42E, CD74HCT42E offers tighter input threshold alignment with legacy TTL but sacrifices voltage flexibility, while SN74HC42N provides identical logic behavior at lower cost and reduced thermal resilience-making CD74HC42E the optimal choice for wide-temperature, multi-rail, or long-lifecycle deployments.

Availability

CD74HC42E is available at Aetrix Electronics and suitable for industrial control panels, aerospace instrumentation, and automotive dashboard systems requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HC42E 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 decades of heritage in high-reliability logic families including the 74HC series.

The CD74HC42E belongs to TI's industry-standard 74HC high-speed CMOS logic portfolio, designed specifically for low-power, wide-temperature BCD decoding in mission-critical industrial, defense, and automotive systems.

FAQ

What is the maximum operating frequency supported by the CD74HC42E?

The CD74HC42E does not specify a maximum clock frequency because it is a combinational logic device without an internal clock. Its usable switching rate depends on propagation delay (12ns typical @ 5V/15pF) and system-level timing margins. In practice, CD74HC42E reliably supports BCD input update rates up to approximately 30MHz under ideal loading conditions, assuming clean input edges and proper decoupling.

Is the CD74HC42E pin-compatible with the older 74LS42 decoder?

Yes, the CD74HC42E is pin-compatible with the 74LS42 in the 16-pin PDIP package and performs the identical 1-of-10 BCD decoding function with active-low outputs. However, CD74HC42E uses CMOS inputs (VIH ≥1.5V @ 2V, ≥3.15V @ 4.5V) rather than TTL thresholds, so direct substitution requires verification that driving sources meet HC input voltage requirements.

Does the CD74HC42E require external pull-up resistors on its outputs?

No, the CD74HC42E features totem-pole CMOS outputs capable of actively driving both high and low logic states. External pull-ups are unnecessary unless implementing wired-OR logic or interfacing with open-drain inputs. When used as intended, each Yx output sources current when inactive (high) and sinks current when active (low), per standard CMOS behavior.

Can the CD74HC42E decode hexadecimal (0–F) inputs, or only BCD (0–9)?

The CD74HC42E decodes only valid BCD inputs (0000–1001, i.e., decimal 0–9). Inputs 1010 through 1111 (decimal 10–15) are treated as invalid, resulting in all ten outputs (Y0–Y9) remaining high. It does not provide hex-to-decimal or 4-to-16 decoding functionality - for that, a CD74HC154 or similar 4-to-16 decoder is required.

What is the recommended bypass capacitor value for the VCC pin of the CD74HC42E?

Texas Instruments recommends a 0.1µF ceramic capacitor placed as close as possible to the VCC pin (Pin 12) and GND (Pin 7) of the CD74HC42E to suppress high-frequency supply noise and ensure stable switching performance. For systems with heavy simultaneous output switching, adding a bulk 10µF electrolytic or tantalum capacitor nearby further improves low-frequency regulation.