Texas Instruments SN74HC42N

Overview

SN74HC42N from Texas Instruments is a 4-bit BCD-to-decimal decoder IC in 16-pin PDIP 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 maximum ICC of 80 µA. It fully decodes valid BCD inputs (0–9), drives up to 10 LSTTL loads, and forces all outputs high for invalid BCD codes - used in address decoding and numeric display selection circuits.

For engineers reviewing the SN74HC42N datasheet, SN74HC42N pinout, SN74HC42N application, or SN74HC42N equivalent, this page delivers verified functional behavior, validated pin assignments, confirmed timing and drive specifications, and real-world substitution guidance - all grounded in TI's SCLS091D datasheet and official packaging documentation.

Technical Context

The SN74HC42N implements full BCD decoding using eight inverters and ten 4-input NAND gates, with input pairs inverted to generate complementary BCD signals for NAND-based decoding logic. Its architecture ensures that only one of ten outputs goes low per valid input (0–9), while all outputs remain high for any invalid 4-bit combination (10–15).

No internal connections exist on pins 3, 5, 12, and 13 (NC), and all unused inputs must be tied to VCC or GND to prevent floating CMOS node instability. The device operates across −40°C to +85°C and supports standard TTL-compatible input thresholds at 5 V (VIH = 3.15 V, VIL = 1.35 V).

Key Specifications

Pinout & Package

SN74HC42N uses a 16-pin plastic dual in-line package (PDIP-N), with 5.08 mm lead pitch and 19.3 mm body width. Pin 1 is located at the top-left corner (notch side), and the package includes four no-connect (NC) terminals.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS42N, SN74HC42N offers lower power, faster speed, and wider voltage range but lacks TTL-level drive strength; compared with CD4555BE, it delivers complete, self-contained BCD decoding without external components - making SN74HC42N optimal for compact, deterministic decimal selection tasks.

Availability

SN74HC42N is available at Aetrix Electronics and suitable for industrial control panels, LED display subsystems, and legacy system upgrades requiring stable component supply and long-term obsolescence management.

Supply support for SN74HC42N 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic solutions with global manufacturing and quality certification.

The SN74HC42N belongs to TI's 74HC high-speed CMOS logic family, designed specifically for pin-compatible upgrades of TTL devices in industrial, instrumentation, and control applications where low power and wide supply range are critical.

FAQ

What is the function of SN74HC42N?

The SN74HC42N is a 4-bit binary-coded decimal (BCD) to decimal decoder that accepts inputs A–D (LSB to MSB) and activates exactly one of ten active-low outputs (0–9) for valid BCD codes. For invalid inputs (10–15), all outputs remain high. This behavior is implemented via internal inverters and NAND gates, as confirmed in the TI SCLS091D datasheet logic diagram and function table.

Does SN74HC42N support 3.3 V operation?

Yes, SN74HC42N supports 3.3 V operation within its specified 2 V to 6 V supply range. At VCC = 3.3 V, VIH is 2.31 V (70% of VCC) and VIL is 0.99 V (30% of VCC), ensuring reliable interfacing with 3.3 V microcontrollers and FPGAs. This is explicitly defined in the "Recommended Operating Conditions" section of the SCLS091D datasheet.

Are pins 3, 5, 12, and 13 on SN74HC42N truly unconnected?

Yes, pins 3, 5, 12, and 13 on SN74HC42N are designated NC (no internal connection) in the TI datasheet, confirmed by both the pin diagram and the note "NC − No internal connection". These pins have no bonding wires or internal silicon connection and must not be used for signal routing, grounding, or power - though they may be tied to GND or VCC per board-level ESD best practices.

Can SN74HC42N drive LEDs directly?

Yes, SN74HC42N can drive LEDs directly in common-cathode configurations: each output sinks up to 4 mA at 5 V (VOL ≤ 0.33 V), sufficient for low-current indicator LEDs with appropriate series resistors (e.g., 330 Ω at 5 V yields ~12 mA total, shared across multiple outputs). However, continuous multi-output activation should respect the device's ±25 mA absolute max output current rating per pin.

How does SN74HC42N handle invalid BCD inputs like 1010 (decimal 10)?

SN74HC42N forces all ten outputs (0–9) high for any invalid BCD input (10–15), as documented in the Function Table and "All Outputs Are High for Invalid BCD Conditions" feature bullet. This behavior is hardwired in the internal NAND gate structure and requires no external logic - providing inherent fault tolerance in decimal-restricted systems such as numeric displays or dial-based controllers.