SN75451B Dual Peripheral Driver

Overview

The SN55451B through SN55454B and SN75451B through SN75454B are dual peripheral drivers designed for use in systems employing TTL logic. This family is functionally interchangeable with and replaces the earlier SN75450 family devices while offering improved performance. The devices are optimized for high-speed operation while ensuring freedom from latch-up conditions. With diode-clamped inputs that simplify circuit design, these drivers are well-suited for a variety of switching and driving applications.

The SN75451B specifically functions as a dual peripheral AND driver (assuming positive logic), with the output of the AND gates internally connected to the bases of npn output transistors. The device is characterized for commercial temperature range operation (0°C to 70°C), while the SN55451B military-grade version operates over -55°C to 125°C.

Features

• Dual peripheral driver with AND gate inputs
• High-speed operation equivalent to SN75450 family
• Diode-clamped inputs for simplified circuit design
• Latch-up free design
• High output current capability
• TTL-compatible inputs
• Wide operating temperature range (commercial and military versions available)
• Improved replacement for SN75450 family devices
• Internal connection from logic gate outputs to transistor bases

Applications

• High-speed logic buffers
• Power drivers for various loads
• Relay drivers for electromechanical systems
• Lamp drivers for indicator lights
• MOS drivers for interfacing with MOSFET circuits
• Line drivers for communication interfaces
• Memory drivers in digital systems
• General purpose switching applications
• Industrial control systems
• Automotive electronics

Electrical Characteristics

Absolute Maximum Ratings

• Supply Voltage (VCC): 7V
• Input Voltage: 5.5V
• Output Voltage: 30V
• Output Current (per driver): 300mA
• Power Dissipation: 1W
• Operating Temperature Range (SN75451B): 0°C to 70°C
• Operating Temperature Range (SN55451B): -55°C to 125°C
• Storage Temperature Range: -65°C to 150°C

Recommended Operating Conditions

• Supply Voltage (VCC): 4.5V to 5.5V
• High-level Input Voltage: 2V min
• Low-level Input Voltage: 0.8V max
• Operating Free-air Temperature (SN75451B): 0°C to 70°C

Switching Characteristics (VCC = 5V, TA = 25°C)

• Propagation Delay Time (Low-to-High): 20ns typical
• Propagation Delay Time (High-to-Low): 25ns typical
• Output Rise Time: 15ns typical
• Output Fall Time: 20ns typical

Package Information

Available Packages

• 14-pin Plastic Dual In-line Package (PDIP)
• 14-pin Small Outline Package (SOIC)
• 14-pin Ceramic Dual In-line Package (CDIP) for military versions

Pin Configuration (PDIP/SOIC)

• Pin 1: 1A (Input A for Driver 1)
• Pin 2: 1B (Input B for Driver 1)
• Pin 3: 1Y (Output for Driver 1)
• Pin 4: GND (Ground)
• Pin 5: 2Y (Output for Driver 2)
• Pin 6: 2B (Input B for Driver 2)
• Pin 7: 2A (Input A for Driver 2)
• Pin 8: VCC (Supply Voltage)
• Pins 9-14: No Connection (NC)

Thermal Characteristics

• Thermal Resistance (PDIP, Junction-to-Air): 80°C/W
• Thermal Resistance (SOIC, Junction-to-Air): 160°C/W
• Maximum Junction Temperature: 150°C

Functional Description

The SN75451B integrates two independent AND gate drivers in a single package. Each driver consists of a two-input AND gate whose output is connected to the base of an npn output transistor. The diode-clamped inputs provide protection against negative transients and ensure proper TTL compatibility. The output transistors are capable of sinking substantial current, making the device suitable for driving various loads.

The internal AND gate functionality means that both inputs must be high for the output transistor to turn on. This provides inherent protection against accidental activation and allows for flexible control schemes. The output stage is designed to handle inductive loads typical in relay and solenoid applications.

Design Considerations

Input Protection

The diode-clamped inputs provide protection against negative-going transients that might otherwise damage the device. For additional protection in harsh environments, series input resistors may be used to limit current during transient events.

Output Considerations

When driving inductive loads, proper flyback protection diodes should be used to protect the output transistors from voltage spikes caused by collapsing magnetic fields. The output current should be limited to 300mA per driver to prevent excessive heating and potential damage.

Power Supply Decoupling

A 0.1μF ceramic capacitor should be placed as close as possible to the VCC and GND pins to minimize power supply noise and ensure stable operation, especially in high-speed switching applications.

Comparison with Previous Generations

The SN75451B offers several improvements over the earlier SN75450 family:

• Guaranteed freedom from latch-up under all operating conditions
• Improved switching speed matching TTL requirements
• More robust output stage design
• Better thermal characteristics
• Enhanced input protection

These improvements make the SN75451B suitable for more demanding applications while maintaining backward compatibility with existing designs using the SN75450 family.