LM2578AN

LM2578AN Switching Regulator Technical Summary

Overview

The LM2578AN is a versatile switching regulator designed for DC-to-DC voltage conversion in buck, boost, and inverting configurations. As an improved version of the LM1578, it offers enhanced performance with higher maximum ratings for total supply voltage and improved efficiency. The device features a unique comparator input stage with separate pins for inverting and non-inverting inputs, simplifying circuit design and PCB layout. With an output capable of switching up to 750 mA and flexible output pin configurations, the LM2578AN is ideal for a wide range of power supply applications.

Key Features

• Wide input voltage range for versatile applications
• Capable of buck, boost, and inverting configurations
• Unique comparator input stage with separate inverting and non-inverting input pins
• Internal 1.0V reference for each input, simplifying design
• Output switching capability up to 750 mA
• Separate collector and emitter output pins for design flexibility
• External current limit terminal (referenced to ground or Vin)
• On-board oscillator with frequency set by external capacitor (1 Hz to 100 kHz typical)
• Improved version of LM1578 with higher maximum ratings
• Thermal shutdown protection
• Cycle-by-cycle current limiting

Applications

The LM2578AN is suitable for a wide variety of power conversion applications, including:

• DC-DC converters
• Negative voltage generators
• Battery chargers
• Power supplies for industrial equipment
• Automotive power systems
• Telecommunications equipment
• Portable electronic devices
• LED drivers
• Solar power systems
• Distributed power systems

Electrical Characteristics

The following table summarizes the key electrical specifications of the LM2578AN:

Absolute Maximum Ratings

• Supply Voltage (Vin): 40V
• Output Switch Voltage: 65V
• Output Switch Current: 750mA
• Oscillator Charging Current: 5mA
• Feedback Input Voltage: -0.3V to +5V
• Current Limit Sense Voltage: -0.3V to +5V
• Operating Junction Temperature: +150°C
• Storage Temperature Range: -65°C to +150°C

Recommended Operating Conditions

• Input Voltage Range: 4V to 40V
• Output Voltage Range: Adjustable based on configuration
• Switching Frequency Range: 1Hz to 100kHz
• Operating Temperature Range: -40°C to +125°C

Electrical Specifications (TA = 25°C, Vin = 20V unless otherwise specified)

• Reference Voltage: 1.00V ± 2%
• Reference Voltage Temperature Coefficient: 100ppm/°C max
• Oscillator Frequency Range: 1Hz to 100kHz
• Output Switch Saturation Voltage: 1.5V max (at 500mA)
• Standby Current: 6mA max
• Current Limit Threshold: 100mV
• Comparator Input Bias Current: 100nA max
• Shutdown Threshold: 0.5V max

Package Information

The LM2578AN is available in a standard 8-pin PDIP (Plastic Dual In-line Package) with the following dimensions and characteristics:

Mechanical Specifications

• Package Type: 8-Pin PDIP
• Package Code: N (for DIP-8)
• JEDEC Standard: MS-001
• Package Body Material: Molded Plastic
• Lead Material: Copper Alloy
• Lead Finish: Matte Tin
• Package Weight: 0.65 grams (approximate)

Package Dimensions

• Overall Length: 9.81mm (0.386 inches)
• Overall Width: 6.35mm (0.250 inches)
• Overall Height: 3.30mm (0.130 inches)
• Lead Pitch: 2.54mm (0.100 inches)
• Lead Width: 0.38mm (0.015 inches)
• Lead Length: 3.30mm (0.130 inches)

Thermal Characteristics

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

Pin Configuration and Functions

The LM2578AN features the following pin configuration:

Pinout Description

• Pin 1: Collector (Output Switch Collector)
• Pin 2: Emitter (Output Switch Emitter)
• Pin 3: Timing Capacitor (Oscillator Timing Input)
• Pin 4: Ground (Circuit Ground)
• Pin 5: Inverting Input (Comparator Inverting Input)
• Pin 6: Non-Inverting Input (Comparator Non-Inverting Input)
• Pin 7: Current Limit (Current Sense Input)
• Pin 8: VCC (Positive Supply Input)

Typical Application Circuits

The LM2578AN can be configured in several standard topologies:

Buck Converter Configuration

In buck mode, the LM2578AN steps down the input voltage. A typical configuration includes an inductor, diode, and output capacitor. The feedback network is connected to maintain the desired output voltage.

Boost Converter Configuration

For boost applications, the component arrangement changes to step up the input voltage. The inductor is placed in series with the input, and the feedback network must be adjusted accordingly.

Inverting Converter Configuration

The inverting configuration generates a negative output voltage from a positive input. This requires careful attention to the feedback network and component selection.

Design Considerations

When designing with the LM2578AN, consider the following:

• Proper heat sinking may be required for high current applications
• External component selection (inductors, capacitors) significantly impacts performance
• PCB layout should minimize high current loop areas
• Feedback network resistors should be precision types for stable output
• Input and output capacitors should be low-ESR types
• Frequency selection affects component size and efficiency

Reliability and Compliance

The LM2578AN meets or exceeds the following standards:

• RoHS compliant
• Lead-free manufacturing process
• ESD protection: 1kV Human Body Model
• Manufactured under ISO 9001 quality systems