74257 Quad 2-Input Multiplexer with 3-State Outputs

Overview

The M54/74HC257 and M54/74HC258 are high-speed CMOS logic devices belonging to the 74HC family. These integrated circuits are quad 2-input multiplexers featuring 3-state outputs, designed for bus-oriented applications. The 74257 is a non-inverting multiplexer, while the 74258 provides inverting functionality. Both devices are fabricated using silicon gate CMOS technology, which ensures low power consumption while maintaining high noise immunity and compatibility with TTL levels.

These multiplexers are commonly used in digital systems for data routing, bus sharing, and signal selection applications. The 3-state outputs allow multiple devices to be connected to a common bus without interference, making them ideal for microprocessor systems and other digital architectures requiring shared data paths.

Features

• High-speed operation: Typical propagation delay of 13ns at VCC = 5V
• Low power consumption: ICC = 4μA maximum at TA = 25°C
• High noise immunity: CMOS technology provides superior noise margins
• Wide operating voltage range: 2V to 6V
• 3-state outputs for bus-oriented applications
• Balanced propagation delays
• Standardized symmetrical output characteristics
• Pin and function compatible with 74LS257
• Available in multiple package options including DIP, SOIC, and TSSOP
• Operating temperature range: -55°C to +125°C (military grade) or -40°C to +85°C (industrial grade)

Applications

The 74257 and 74258 multiplexers find use in a wide variety of digital systems, including:

• Data routing and selection in microprocessor systems
• Bus sharing and multiplexing in digital architectures
• Memory address multiplexing
• Input/output port selection
• Data acquisition systems
• Communication systems
• Test and measurement equipment
• Industrial control systems
• Automotive electronics
• Consumer electronics

Electrical Characteristics

Absolute Maximum Ratings

• Supply Voltage (VCC): -0.5V to +7V
• Input Voltage (VI): -0.5V to VCC + 0.5V
• Output Voltage (VO): -0.5V to VCC + 0.5V
• Input Diode Current (IIK): ±20mA
• Output Diode Current (IOK): ±20mA
• Output Source or Sink Current (IO): ±25mA
• Supply Current (ICC or IGND): ±50mA
• Storage Temperature Range (TSTG): -65°C to +150°C

Recommended Operating Conditions

• Supply Voltage (VCC): 2V to 6V
• Input Voltage (VI): 0V to VCC
• Output Voltage (VO): 0V to VCC
• Operating Temperature Range (TA): -40°C to +85°C (74HC) or -55°C to +125°C (54HC)

DC Electrical Characteristics

• High-Level Input Voltage (VIH): 70% of VCC
• Low-Level Input Voltage (VIL): 30% of VCC
• High-Level Output Voltage (VOH): VCC - 0.1V (IO = -20μA)
• Low-Level Output Voltage (VOL): 0.1V (IO = 20μA)
• Input Leakage Current (II): ±1μA at VCC = 6V
• Quiescent Supply Current (ICC): 4μA maximum at VCC = 6V

AC Electrical Characteristics

• Propagation Delay (A, B to Y): 13ns typical at VCC = 5V
• Output Enable Time (OE to Y): 14ns typical at VCC = 5V
• Output Disable Time (OE to Y): 16ns typical at VCC = 5V
• Input Capacitance (CI): 3.5pF typical
• Power Dissipation Capacitance (CPD): 23pF typical at VCC = 5V

Package Information

Available Packages

• 16-pin Plastic Dual In-line Package (PDIP)
• 16-pin Small Outline Integrated Circuit (SOIC)
• 16-pin Shrink Small Outline Package (SSOP)
• 16-pin Thin Shrink Small Outline Package (TSSOP)

Package Dimensions (PDIP Example)

• Total Height: 4.44mm maximum
• Body Length: 19.30mm maximum
• Body Width: 6.35mm maximum
• Lead Pitch: 2.54mm
• Lead Length: 3.30mm minimum

Thermal Characteristics

• Thermal Resistance, Junction-to-Ambient (θJA): 80°C/W (PDIP)
• Thermal Resistance, Junction-to-Case (θJC): 20°C/W (PDIP)

Functional Description

The 74257 contains four identical 2-input multiplexers with common select and output enable inputs. Each multiplexer selects one of two data inputs (A or B) under control of the select input (S). When the output enable (OE) is low, the selected data appears at the output (Y). When OE is high, the outputs are in a high-impedance state.

The truth table for one multiplexer section is as follows:

• OE | S | Output
• H | X | Z (high impedance)
• L | L | A (data input)
• L | H | B (data input)

Design Considerations

Power Supply Decoupling

A 0.1μF ceramic capacitor should be connected between VCC and GND near each device to minimize noise and ensure stable operation. For high-speed or high-noise environments, additional decoupling may be required.

Unused Inputs

All unused inputs must be tied to either VCC or GND through a resistor to prevent floating inputs which can cause excessive power consumption and unpredictable operation.

Output Loading

The outputs should not be loaded beyond the specified maximum current ratings. When driving multiple inputs, the total fan-out should be calculated to ensure proper voltage levels are maintained.

Quality and Reliability

The 74257 is manufactured under strict quality control procedures and meets or exceeds the following reliability standards:

• ESD Protection: Human Body Model ≥ 2000V
• Latch-up Immunity: ≥ 250mA
• Burn-in: 100% tested at elevated temperature
• Data Retention: 10 years minimum

Ordering Information

The device is available in several variants differentiated by package type, temperature range, and quality grade. Typical ordering codes include:

• 74HC257N: PDIP package, commercial temperature range
• 74HC257D: SOIC package, commercial temperature range
• 74HC257PW: TSSOP package, commercial temperature range
• 54HC257F: Ceramic flatpack, military temperature range