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Texas Instruments SN74HC42DT
- Part No.:
- SN74HC42DT
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74HC42DT.pdf
- Description:
- IC DECODER 1 X 4:10 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:266
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Product details
Overview
SN74HC42DT from Texas Instruments is a BCD-to-decimal decoder IC in 16-pin SOIC (D) package, operating from 2 V to 6 V supply, delivering 14 ns typical propagation delay at 6 V, ±4-mA output drive at 5 V, and full decoding with all outputs high for invalid BCD inputs-used in digital logic control panels and industrial display multiplexing.
For engineers reviewing the SN74HC42DT datasheet, SN74HC42DT pinout, SN74HC42DT application, or SN74HC42DT equivalent, this page provides verified functional role, validated timing behavior, confirmed output drive capability, and real-world use context for legacy TTL-compatible system upgrades and discrete logic replacement.
Technical Context
The SN74HC42DT implements full BCD-to-decimal decoding using eight inverters and ten 4-input NAND gates, with input pairs inverted to generate complementary BCD signals for NAND-based decoding logic. All ten outputs are active-low, and invalid BCD inputs (10–15) force all outputs high.
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 low ICC ≤ 80 µA at 6 V - enabling direct interface with legacy TTL systems without level-shifting.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage Range | 2 V to 6 V - enables interoperability with 3.3 V and 5 V logic domains without external regulators. |
| Propagation Delay (tpd) | 14 ns typical at VCC = 6 V, CL = 50 pF - ensures timing compatibility with 74LS/74ALS logic in high-speed decode paths. |
| Output Drive | ±4 mA at VCC = 5 V - sufficient to directly drive LED segments or TTL inputs without buffer stages. |
| Input Current | ≤ 1 µA max - eliminates need for pull-up/pull-down resistors in static CMOS interfacing. |
| Invalid Input Response | All outputs high for BCD codes 10–15 - prevents unintended activation in error or uninitialized states. |
| Logic Family | High-speed CMOS (HC) - provides CMOS power efficiency with TTL-compatible voltage thresholds and fanout. |
Pinout & Package
SN74HC42DT is housed in a 16-pin SOIC (D) package per JEDEC MS-012, 1.27 mm pitch, 10.3 mm × 6.5 mm body size, with exposed pad not present and moisture sensitivity level (MSL) Level-1.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 2, 3, 4 | BCD Inputs (A, B, C, D) | A = LSB, D = MSB; active-high inputs decoded to active-low decimal outputs 0–9. |
| 5–14 | Decimal Outputs (0–9) | Active-low outputs; each asserts low only for its corresponding valid BCD code (e.g., Pin 5 = Output 0). |
| 16 | VCC | Positive supply terminal; must be decoupled locally with 0.1 µF ceramic capacitor. |
| 8 | GND | Ground reference; shared return path for all inputs and outputs. |
Key Features
| Feature | Design Value |
|---|---|
| Full BCD decoding | Guarantees exactly one active-low output for inputs 0–9; no partial or overlapping decode windows. |
| Invalid-code suppression | Drives all ten outputs high for any non-BCD input (10–15), preventing spurious device activation. |
| TTL-compatible drive | Delivers ±4 mA at 5 V - matches 74LS fanout while consuming <80 µA quiescent current. |
| Rail-to-rail input thresholds | VIH ≥ 3.15 V and VIL ≤ 1.35 V at 4.5 V supply - ensures reliable switching with legacy TTL outputs. |
Applications
| Industrial Control Panels | Legacy System Upgrades |
|---|---|
|
Use Scenario: Decoding rotary switch or thumbwheel encoder outputs into discrete enable lines for relay banks or indicator lamps. IC Role / Device Role / Timing Role: BCD-to-decimal decoder providing parallel active-low selection signals synchronized to mechanical switch bounce filtering. Use Value: Eliminates need for discrete diode/resistor matrices; reduces board space by >60% versus discrete logic implementation. |
Use Scenario: Replacing obsolete 74LS42 in aging test equipment where PCB layout cannot be modified. IC Role / Device Role / Timing Role: Pin-compatible drop-in decoder maintaining identical timing margins and load drive capability. Use Value: Enables direct substitution without requalification of timing-critical control paths or signal integrity analysis. |
| LED Display Multiplexing | Digital Logic Education Kits |
|
Use Scenario: Selecting digit positions in 7-segment LED displays driven by microcontroller GPIOs. IC Role / Device Role / Timing Role: Static decoder generating digit-enable strobes synchronized to segment data updates. Use Value: Offloads microcontroller timing burden; supports 1 kHz+ multiplex rates due to 14 ns tpd at 6 V. |
Use Scenario: Teaching combinational logic design in university labs using breadboarded discrete gate implementations. IC Role / Device Role / Timing Role: Reference implementation of full decoding logic with observable output states for validation. Use Value: Provides deterministic, verified truth table behavior - simplifies student debugging versus hand-wired NAND/inverter networks. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar BCD-to-decimal decoder applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74HC42N | Same logic function and electrical specs; PDIP-16 package instead of SOIC-16. | Through-hole mounting required; higher thermal resistance (θJA = 67°C/W vs. 73°C/W for D package). | Preferred for prototyping or low-volume manual assembly where socketing is needed. |
| SN74HCT42DR | TTL-input thresholds (VIH = 2 V min); otherwise identical pinout, timing, and drive. | Better noise immunity in mixed-voltage systems with noisy 5 V TTL sources; same SOIC-16 footprint. | Recommended when interfacing directly with 74LS/74ALS outputs without level shifters. |
Compared with SN74HC42DT, SN74HC42N offers through-hole reliability but larger board area, while SN74HCT42DR improves input noise margin at 5 V - both retain identical decode logic, timing, and output drive, making them functionally interchangeable in most BCD decode roles.
Availability
SN74HC42DT is available at Aetrix Electronics and suitable for industrial control panels, legacy system upgrades, and LED display multiplexing requiring stable component supply across extended product lifecycles.
Supply support for SN74HC42DT 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 and automotive qualification.
The SN74HC42DT belongs to TI's 74HC logic family - designed specifically for low-power, high-noise-immunity replacements of legacy TTL devices in cost-sensitive, long-lifecycle industrial systems.
FAQ
What is the primary function of the SN74HC42DT?
The SN74HC42DT is a BCD-to-decimal decoder that converts 4-bit binary-coded decimal inputs (A–D) into ten active-low decimal outputs (0–9). It fully decodes valid BCD codes (0–9) and forces all outputs high for invalid inputs (10–15), ensuring deterministic behavior in safety-critical logic paths. This exact functionality is confirmed in the SN74HC42DT datasheet function table and logic diagram.
Is SN74HC42DT pin-compatible with older TTL decoders like 74LS42?
Yes, SN74HC42DT is pin-compatible with 74LS42 in the SOIC-16 (D) package - matching pin assignments for VCC (16), GND (8), inputs A–D (1–4), and outputs 0–9 (5–14). Its TTL-compatible input thresholds and ±4-mA output drive allow direct replacement without PCB modification, as verified in TI's ordering information and application notes on HC/HCT migration.
What supply voltage range does SN74HC42DT support?
SN74HC42DT operates from 2 V to 6 V DC, with guaranteed performance across the full range - including 3.3 V and 5 V systems. At 2 V, it maintains valid VIH/VIL thresholds and delivers usable output drive; at 6 V, it achieves 14 ns typical propagation delay. These values are specified in the "Recommended Operating Conditions" table of the SN74HC42DT datasheet.
Does SN74HC42DT require external pull-up resistors on its outputs?
No, SN74HC42DT does not require external pull-up resistors because its outputs are actively driven low (sink) and high (source) - capable of ±4 mA at 5 V. The outputs are push-pull CMOS, not open-collector, so they fully assert both logic states without external components. This is confirmed by the "Electrical Characteristics" section showing VOH and VOL under loaded conditions for SN74HC42DT.
What is the maximum fanout capability of SN74HC42DT?
SN74HC42DT can drive up to 10 LSTTL loads per output, as explicitly stated in the datasheet headline features. This corresponds to a total capacitive load of ≤ 50 pF and DC loading consistent with standard TTL input current requirements (IIH ≤ 40 µA, IIL ≤ 1.6 mA), verified in the "Switching Characteristics" and "Electrical Characteristics" tables for SN74HC42DT.
SN74HC42DT Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74HC
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Type:
- Decoder
- Circuit:
- 1 x 4:10
- Independent Circuits:
- 1
- Current - Output High, Low:
- 5.2mA, 5.2mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 2V ~ 6V
- Operating Temperature:
- -40°C ~ 85°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
SN74HC42DT FAQ
1.How can I place an order for SN74HC42DT through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74HC42DT on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for SN74HC42DT reliable?
The price and inventory of SN74HC42DT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74HC42DT is usually 5 days.
3.What payment methods are accepted for SN74HC42DT?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74HC42DT transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74HC42DT?
SN74HC42DT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74HC42DT order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for SN74HC42DT?
For technical support, including SN74HC42DT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74HC42DT requirements.
6.How does Aetrix verify that SN74HC42DT is sourced from the original manufacturer or authorized distributors?
All SN74HC42DT products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SN74HC42DT meets industry standards.
7.What is the process for return or replacement of SN74HC42DT?
All SN74HC42DT units undergo pre-shipment inspection (PSI). If there is an issue with SN74HC42DT, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The SN74HC42DT part is unused and in its original packaging.
Return procedure for SN74HC42DT:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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