Texas Instruments CD74HC42M

Overview

CD74HC42M 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), operating across 2V–6V supply range with 12ns typical propagation delay at 5V/15pF and -55°C to +125°C temperature range - used in industrial control panels for discrete digit selection in 7-segment driver interfaces.

For engineers reviewing the CD74HC42M datasheet, CD74HC42M pinout, CD74HC42M application, or CD74HC42M equivalent, key selection considerations include its SOIC-16 package compatibility, LSTTL-load driving capability (10 loads), CMOS input noise immunity (30% of VCC), and BCD decoding logic behavior under non-valid input conditions (all outputs high).

Technical Context

The CD74HC42M implements standard combinational logic decoding with active-low outputs and no internal latching; all ten outputs remain high for invalid BCD inputs (10–15 decimal), ensuring fail-safe digit disablement. Its silicon-gate CMOS architecture delivers LSTTL-compatible speed while consuming significantly less power than legacy TTL equivalents.

Input thresholds are rail-proportional (VIH = 70% VCC, VIL = 30% VCC at 5V), enabling robust noise rejection; output drive strength supports ±25mA per pin with CMOS- and TTL-load compatibility, and propagation delay varies predictably with supply voltage (26ns at 6V, 30ns at 4.5V, 150ns at 2V under 50pF load).

Key Specifications

Pinout & Package

CD74HC42M is supplied in a 16-pin Small Outline Integrated Circuit (SOIC) package with standard 1.27mm pitch, JEDEC MS-012AC compliant, moisture sensitivity level 1 (260°C reflow compatible), and RoHS-compliant NiPdAu lead finish.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC42M, CD74HCT42E offers tighter input threshold alignment with legacy TTL but sacrifices supply flexibility, while SN74LS42N provides guaranteed interoperability in pure TTL systems at the cost of power and speed - making CD74HC42M optimal for new designs requiring wide-VCC operation, low quiescent current, and extended temperature support.

Availability

CD74HC42M is available at Aetrix Electronics and suitable for industrial control panels, avionics annunciator systems, and automotive dashboard clusters requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HC42M 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 90 years of innovation in high-reliability IC design and manufacturing.

The CD74HC42M belongs to TI's legacy HC logic family, engineered for pin-compatible migration from TTL while delivering CMOS power efficiency and enhanced noise immunity in industrial and aerospace timing-critical applications.

FAQ

What is the maximum clock frequency supported by CD74HC42M for reliable BCD decoding?

The CD74HC42M is a combinational logic device with no internal clock; its maximum usable input transition rate depends on propagation delay and system setup/hold timing. With a typical 12ns propagation delay at 5V, it supports BCD input updates up to approximately 40 MHz in ideal conditions - though real-world limits are governed by PCB trace length, load capacitance, and driver slew rate rather than an intrinsic clock specification. The CD74HC42M does not require a clock signal to operate.

Does CD74HC42M support 3.3V operation, and what are the implications for noise margin?

Yes, CD74HC42M supports 3.3V operation within its 2V–6V supply range. At VCC = 3.3V, input high threshold (VIH) is 2.31V (70% of 3.3V) and input low threshold (VIL) is 0.99V (30% of 3.3V), yielding ±0.66V noise margins - sufficient for clean 3.3V CMOS interfaces. The CD74HC42M maintains full functionality and specified timing across this voltage, with propagation delay increasing to ~20ns at 3.3V/15pF per datasheet switching specs.

How does CD74HC42M behave when presented with invalid BCD inputs such as 1010 (decimal 10)?

Per the truth table and functional description, the CD74HC42M asserts none of the Y0–Y9 outputs for invalid BCD codes (10–15 decimal). All ten outputs remain in the high state, providing a fail-safe condition that prevents erroneous digit activation. This behavior is inherent to the logic design and requires no external circuitry - a key reliability feature confirmed in the CD74HC42M datasheet's truth table and description section.

Can CD74HC42M drive LEDs directly, and what current-limiting considerations apply?

The CD74HC42M can sink up to 25mA per output pin, sufficient to drive standard 2–20mA LEDs directly when configured in common-anode topology (LED anode to VCC, cathode to Yx). A series resistor must be calculated using VOH/VOL specs: at 5V, VOL ≤ 0.1V ensures >4.9V across the resistor. For a 10mA LED, R ≈ (5V − 1.8V − 0.1V)/0.01A = 310Ω. The CD74HC42M's total package current limit (±50mA ICC/IGND) constrains simultaneous multi-output drive.

Is CD74HC42M pin-compatible with CD74HCT42 and SN74LS42, and what are the layout implications?

CD74HC42M (SOIC-16) and CD74HCT42E (PDIP-16) share identical pin functions but differ in package type and footprint - SOIC cannot be substituted for PDIP without PCB redesign. CD74HC42M and SN74LS42N share the same 16-pin DIP pinout, but CD74HC42M is only available in SOIC; a SOIC-to-DIP adapter would be needed for physical replacement. The CD74HC42M's logic function and pin assignments match both parts exactly, enabling schematic reuse across variants.