Technical Summary for 74240 Series Logic Components

Technical Summary: M54/74HC240, HC241, and HC244 Octal Buffer/Line Drivers

Overview

The M54/74HC240, HC241, and HC244 are high-speed octal buffer and line driver integrated circuits belonging to the 74HC family of logic devices. These components are designed using silicon gate CMOS technology, offering a balance of high-speed operation and low power consumption. The devices feature inverting (HC240) and non-inverting (HC241, HC244) buffer functionality, making them suitable for a wide range of digital signal buffering and driving applications.

These octal buffers are particularly useful in bus-oriented systems where signal integrity and fan-out capabilities are critical. The series provides improved performance and lower power consumption compared to equivalent LSTTL devices while maintaining compatibility with standard CMOS and TTL logic levels.

Features

High-Speed Operation: Typical propagation delay of 8ns at V_CC = 5V
Low Power Consumption: Typical I_CC of 4μA at room temperature
Wide Operating Voltage Range: 2V to 6V DC supply voltage
High Noise Immunity: Characteristic of CMOS technology
Output Drive Capability: 15 LSTTL loads
Balanced Propagation Delays: Ensures signal integrity in synchronous systems
Three-State Outputs: HC241 and HC244 feature three-state outputs for bus-oriented applications
Pin-Compatible Replacements: Direct replacements for 74LS240, 74LS241, and 74LS244
ESD Protection: All inputs and outputs protected against electrostatic discharge

Applications

The 74240 series components find use in numerous digital systems requiring signal buffering and line driving:

Bus Drivers: For driving heavily loaded or long transmission lines in microprocessor systems
Memory Address Drivers: In systems with large memory arrays
Clock Distribution Networks: For buffering and distributing clock signals
Input/Output Ports: As interface buffers between different logic families
General Purpose Logic: In various digital systems requiring signal conditioning
Backplane Drivers: For driving signals across backplanes in modular systems
Industrial Control Systems: Where robust signal transmission is required

Electrical Characteristics

Absolute Maximum Ratings

Supply Voltage (V_CC): -0.5V to +7V
Input Voltage (V_IN): -0.5V to V_CC + 0.5V
Output Voltage (V_OUT): -0.5V to V_CC + 0.5V
Operating Temperature Range: -55°C to +125°C (M54 series), -40°C to +85°C (74 series)
Storage Temperature Range: -65°C to +150°C

DC Characteristics (V_CC = 4.5V to 5.5V, T_A = 25°C)

High-Level Input Voltage (V_IH): 3.15V min
Low-Level Input Voltage (V_IL): 1.35V max
High-Level Output Voltage (V_OH): 3.98V min (I_OH = -4mA)
Low-Level Output Voltage (V_OL): 0.26V max (I_OL = 4mA)
Input Leakage Current (I_IN): ±1μA max
Quiescent Supply Current (I_CC): 4μA typical, 20μA max

AC Characteristics (V_CC = 5V, T_A = 25°C)

Propagation Delay (t_PD): 8ns typical, 15ns max (A to Y)
Output Transition Time (t_THL, t_TLH): 6ns typical, 15ns max
Input Capacitance (C_IN): 3.5pF typical
Three-State Output Enable Time (t_PZH, t_PZL): 15ns max (HC241/HC244)
Three-State Output Disable Time (t_PHZ, t_PLZ): 15ns max (HC241/HC244)

Package Information

The 74240 series components are available in several industry-standard packages:

20-pin Plastic Dual In-line Package (PDIP): 0.3" wide body, suitable for through-hole mounting
20-pin Small Outline Package (SOIC): 0.15" body width, surface-mount version
20-pin Shrink Small Outline Package (SSOP): 0.15" body width, more compact than SOIC
20-pin Thin Shrink Small Outline Package (TSSOP): 0.173" body width, 1.0mm pitch

Pin Configuration (HC240 Example)

Pins 1, 19: Output Enable (active low)
Pins 2-9: Inputs (A1-A8)
Pins 18-11: Outputs (Y1-Y8, inverted)
Pin 10: Ground (GND)
Pin 20: Positive Supply (V_CC)

Functional Description

The HC240, HC241, and HC244 each contain eight buffers with different configurations:

HC240: Octal inverting buffer with two independent output enable controls (4 buffers per enable)
HC241: Octal non-inverting buffer with two independent output enable controls (4 buffers per enable)
HC244: Octal non-inverting buffer with single output enable control for all eight buffers

When the output enable inputs are active (low for HC240, high for HC241/HC244), the outputs follow the inputs (inverted for HC240). When disabled, the outputs enter a high-impedance state, making these devices particularly useful for bus sharing applications.