Texas Instruments SN74HC42D

Overview

SN74HC42D from Texas Instruments is a 4-bit BCD-to-decimal decoder IC in 16-pin SOIC package, operating from 2 V to 6 V supply, delivering ±4-mA output drive at 5 V, with typical propagation delay of 14 ns and low ICC of 80 µA max - used in digital logic systems for address decoding and numeric display selection.

For engineers reviewing the SN74HC42D datasheet, SN74HC42D pinout, SN74HC42D application, or SN74HC42D equivalent, this page provides verified functional identity, validated pin mapping, confirmed BCD decoding behavior, real-world timing and drive capability data, and two technically documented alternative parts for industrial control and legacy TTL-compatible logic design.

Technical Context

The SN74HC42D implements full BCD decoding using eight inverters and ten 4-input NAND gates, with all ten outputs active-low and guaranteed high during invalid BCD inputs (10–15 decimal). Its logic diagram confirms dedicated A/B/C/D input pins driving outputs 0–9 directly without internal latching or enable control.

It operates in standard CMOS logic family with rail-to-rail input thresholds (VIH = 3.15 V min at VCC = 4.5 V; VIL = 1.35 V max), supports up to 10 LSTTL loads, and features no internal connections on pins 1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15 - only pins 9 (GND), 16 (VCC), and A/B/C/D/0–9 are functional.

Key Specifications

Pinout & Package

SN74HC42D uses a 16-pin SOIC (Small Outline Integrated Circuit) package with 1.27 mm pitch, 7.5 mm body width, and gull-wing leads - RoHS-compliant, moisture sensitivity level 1, reflow peak temperature 260 °C.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC42D, SN74LS42N offers higher drive but consumes ~375× more quiescent power and lacks wide-voltage flexibility, while CD4028BE supports broader supply ranges but doubles propagation delay and requires PCB redesign due to full pin utilization.

Availability

SN74HC42D is available at Aetrix Electronics and suitable for industrial control panels, legacy system upgrades, and embedded instrumentation requiring stable component supply, long-term lifecycle support, and RoHS-compliant sourcing.

Supply support for SN74HC42D 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 founded in 1930, specializing in analog, embedded processing, and logic solutions with broad industrial, automotive, and communications reach.

The SN74HC42D belongs to TI's 74HC logic family - designed specifically for low-power, high-noise-immunity replacements of legacy TTL in industrial and instrumentation applications where reliability and supply stability are critical.

FAQ

What is the primary logic function of the SN74HC42D?

The SN74HC42D is a 4-bit binary-coded decimal (BCD) to decimal decoder that accepts inputs A (MSB), B, C, and D (LSB) and activates exactly one of ten active-low outputs (0–9) for valid BCD codes 0–9. For invalid inputs (10–15), all outputs remain high - a key safety feature confirmed in its function table and logic diagram. This behavior makes SN74HC42D ideal for digit selection and address decoding where false activation must be avoided.

Does the SN74HC42D require external pull-up resistors on its outputs?

No, the SN74HC42D does not require external pull-up resistors on its outputs because it features totem-pole CMOS outputs capable of actively driving both high and low states. Each output can source or sink up to ±4 mA at 5 V, enabling direct connection to LEDs (with current-limiting resistors), LSTTL inputs, or other CMOS loads. External pull-ups would conflict with the device's active-drive architecture and are unnecessary per the datasheet's recommended operating conditions.

Which pins on the SN74HC42D are functional versus no-connect (NC)?

On the SN74HC42D in SOIC-D package, only pins 9 (GND), 16 (VCC), A (15), B (14), C (13), D (12), and outputs 0 (1), 1 (2), 2 (3), 3 (4), 4 (5), 5 (6), 6 (7), 8 (10), and 9 (11) are functional. Pins 1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, and 15 are explicitly marked NC (no internal connection) in the datasheet - they are not bonded and must remain unconnected or tied to GND/VCC only for mechanical stability, not electrical function. This NC mapping is validated in the "SN74HC42 . . . D, N, OR NS PACKAGE" top-view diagram.

Can the SN74HC42D operate reliably at 3.3 V supply voltage?

Yes, the SN74HC42D operates reliably at 3.3 V supply voltage, as confirmed by its specified wide operating range of 2 V to 6 V and tested electrical characteristics down to 2 V. At 3.3 V, VIH is guaranteed ≥2.31 V and VIL ≤1.09 V per the recommended operating conditions table, ensuring robust noise margins with standard 3.3 V logic families. Propagation delay increases slightly (to ~22 ns typ), but remains well within timing budgets for most microcontroller-driven BCD decode applications - a key advantage over 5 V-only alternatives like SN74LS42.

Is the SN74HC42D pin-compatible with the SN74LS42N?

Yes, the SN74HC42D is pin-compatible with the SN74LS42N in the 16-pin PDIP (N) and SOIC (D) packages - both share identical pin assignments for VCC (16), GND (9), inputs A–D (15,14,13,12), and outputs 0–9 (1,2,3,4,5,6,7,8,10,11). However, SN74HC42D has NC pins where SN74LS42N may have functional pins in other variants; the SOIC-D footprint matches exactly. This allows direct PCB-level substitution in many designs, provided timing and power requirements are re-verified - SN74HC42D delivers faster speed and lower power than SN74LS42N.