7442 Technical Summary

7442 - BCD to Decimal Decoder Technical Summary

Overview

The 7442 is a high-speed BCD (Binary-Coded Decimal) to decimal decoder integrated circuit designed for digital logic applications. This device converts a 4-bit binary input into one of ten mutually exclusive outputs, making it ideal for numeric display decoding and digital system control applications. The 7442 features active-low outputs and is designed with high-speed operation in mind, ensuring reliable performance in time-critical applications.

As a member of the 7400 series of TTL logic devices, the 7442 offers robust performance characteristics including wide operating voltage range, good noise immunity, and compatibility with other TTL family components. The device is packaged in a standard 16-pin DIP (Dual In-line Package) format, making it suitable for both prototyping and production applications.

Features

High-speed decoding operation with typical propagation delay of 15ns
4-bit BCD input with 10 active-low decimal outputs
Standard TTL power supply voltage range (4.75V to 5.25V)
Designed for high noise immunity with 0.4V noise margin
Low power consumption (typical ICC of 20mA)
Input clamping diodes for improved transient response
Wide operating temperature range (0°C to +70°C commercial grade)
Fully compatible with all 7400 series TTL devices
Outputs can sink up to 16mA for driving indicators or relays
Inputs are compatible with standard TTL, DTL, and CMOS logic levels

Applications

The 7442 finds application in numerous digital systems requiring binary to decimal conversion:

Numeric Display Systems

Driving 7-segment displays or other numeric indicators through appropriate driver circuits
Digital Control Systems

Address decoding in microprocessor systems and memory selection circuits
Industrial Automation

Machine control systems requiring precise output selection based on binary inputs
Test Equipment

Function selection in measurement and testing instruments
Telecommunications

Channel selection and routing in communication systems

Electrical Characteristics

Absolute Maximum Ratings

Supply Voltage (VCC): 7V
Input Voltage (VIN): 5.5V
Operating Free Air Temperature Range: 0°C to +70°C
Storage Temperature Range: -65°C to +150°C

Recommended Operating Conditions

Supply Voltage (VCC): 4.75V to 5.25V
High-Level Input Voltage (VIH): 2V min
Low-Level Input Voltage (VIL): 0.8V max
Operating Ambient Temperature: 0°C to +70°C

DC Electrical Characteristics

High-Level Output Voltage (VOH): 2.4V min (VCC = min, IOH = -400μA)
Low-Level Output Voltage (VOL): 0.4V max (VCC = min, IOL = 16mA)
Input Clamp Voltage (VIK): -1.5V max (VCC = min, II = -18mA)
Power Supply Current (ICC): 20mA max (VCC = max, all outputs open)

AC Electrical Characteristics

Propagation Delay Time (tPLH): 15ns max (CL = 15pF, RL = 400Ω)
Propagation Delay Time (tPHL): 22ns max (CL = 15pF, RL = 400Ω)
Input Capacitance (CIN): 3pF typical
Power Dissipation Capacitance (CPD): 20pF typical

Package Information

Physical Dimensions

The 7442 is available in a standard 16-pin plastic dual in-line package (PDIP) with the following dimensions:

Package Width: 7.62mm (0.300 inches)
Package Length: 19.3mm (0.760 inches)
Lead Pitch: 2.54mm (0.100 inches)
Lead Width: 0.38mm (0.015 inches)
Lead Length: 3.3mm (0.130 inches)

Pin Configuration

Pin 1: Output 0 (active low)
Pin 2: Output 1 (active low)
Pin 3: Output 2 (active low)
Pin 4: Output 3 (active low)
Pin 5: Output 4 (active low)
Pin 6: Output 5 (active low)
Pin 7: Output 6 (active low)
Pin 8: Ground (GND)
Pin 9: Output 7 (active low)
Pin 10: Output 8 (active low)
Pin 11: Output 9 (active low)
Pin 12: D input (LSB)
Pin 13: C input
Pin 14: B input
Pin 15: A input (MSB)
Pin 16: VCC (+5V supply)

Thermal Characteristics

Thermal Resistance, Junction-to-Air (θJA): 80°C/W
Thermal Resistance, Junction-to-Case (θJC): 35°C/W
Maximum Junction Temperature (TJ): 150°C

Functional Description

The 7442 operates as a 4-line to 10-line decoder where the four input lines (A, B, C, D) represent a BCD code. The ten outputs (0 through 9) are active-low, meaning the selected output goes to logic low while all others remain high. The device features internal logic gates that ensure only one output is active (low) for any valid BCD input combination (0000 to 1001). For invalid BCD inputs (1010 to 1111), all outputs remain inactive (high).

The decoder implements the following logic function for each output: Output n = (A'·B'·C'·D') for n=0 through (A·B'·C·D) for n=9, where ' indicates logical inversion.

Design Considerations

Unused inputs should be tied to ground or VCC through appropriate resistors
For high-speed operation, keep input transition times below 20ns
When driving capacitive loads, consider adding series resistors to limit current spikes
For systems with long signal paths, proper termination should be used to prevent reflections
Power supply decoupling (0.1μF ceramic capacitor) should be placed close to the VCC pin