LM2670 - 3A Step-Down Switching Voltage Regulator

Overview

The LM2670 series is a family of monolithic integrated circuit step-down (buck) switching regulators designed to deliver up to 3A of output current with outstanding line and load regulation characteristics. These regulators incorporate all the active functions needed for an efficient buck converter solution, making them ideal for a wide range of power supply applications.

Using advanced DMOS power switch technology with low ON-resistance, the LM2670 achieves high efficiency operation exceeding 90%, significantly reducing heat dissipation compared to linear regulators. The series includes fixed output voltage versions (3.3V, 5V, and 12V) as well as an adjustable output variant, providing design flexibility for various system requirements.

Key Features

• High Efficiency: Up to 94% efficiency reduces power loss and heat generation
• Wide Input Voltage Range: 8V to 40V operation
• High Output Current: Up to 3A continuous output current
• Multiple Output Options: Fixed 3.3V, 5V, 12V or adjustable output versions
• Excellent Line Regulation: ±0.15% typical
• Superior Load Regulation: ±0.3% typical
• Integrated Power Switch: Low ON-resistance DMOS FET (typically 0.15Ω)
• Frequency Compensation: Internal compensation simplifies design
• Switching Frequency: 260kHz fixed frequency operation
• Protection Features: Thermal shutdown and current limit protection
• Minimal External Components: Requires only 5 external components for basic operation

Applications

The LM2670 is suitable for a wide variety of applications requiring efficient DC-DC voltage conversion:

• Industrial power systems
• Automotive electronics
• Distributed power systems
• Battery-powered equipment
• Telecommunications equipment
• Computer peripherals
• Embedded systems
• LED drivers
• Point-of-load regulation
• Consumer electronics

Electrical Characteristics

Absolute Maximum Ratings

• Input Voltage (VIN): 45V
• Switch Voltage (VSW): 45V
• Feedback Pin Voltage (VFB): -0.3V to +40V
• Operating Junction Temperature: 125°C
• Storage Temperature Range: -65°C to +150°C

Recommended Operating Conditions

• Input Voltage Range: 8V to 40V
• Output Current: 0A to 3A
• Operating Temperature Range: -40°C to +125°C

Typical Performance Characteristics

• Efficiency: 90% to 94% (depending on input/output conditions)
• Quiescent Current: 5mA typical
• Standby Current: 50μA typical (shutdown mode)
• Line Regulation: ±0.15% (8V ≤ VIN ≤ 40V)
• Load Regulation: ±0.3% (0A ≤ IOUT ≤ 3A)
• Output Voltage Accuracy: ±2% (fixed voltage versions)
• Current Limit Threshold: 3.5A typical

Package Information

The LM2670 is available in several package options to accommodate different design requirements:

TO-220 Package (7-lead)

• Package Type: Through-hole mounting
• Thermal Resistance (Junction-to-Air): 50°C/W
• Dimensions: 10.16mm x 8.89mm x 4.45mm (typical)
• Recommended PCB Pad Layout: 11.5mm x 10.5mm

TO-263 Package (7-lead)

• Package Type: Surface mount (D2PAK)
• Thermal Resistance (Junction-to-Air): 40°C/W
• Dimensions: 10.28mm x 9.65mm x 4.57mm (typical)
• Recommended PCB Pad Layout: 10.5mm x 9.8mm

LLP Package (8-lead)

• Package Type: Leadless surface mount
• Thermal Resistance (Junction-to-Air): 45°C/W
• Dimensions: 5.0mm x 6.0mm x 0.8mm (typical)
• Recommended PCB Pad Layout: 5.2mm x 6.2mm

Design Considerations

Input Capacitor Selection

A low ESR aluminum electrolytic or tantalum capacitor is recommended for the input filter. The capacitor should be rated for at least the maximum input voltage and should be placed as close as possible to the VIN and GND pins of the regulator.

Output Capacitor Selection

The output capacitor affects both the output ripple voltage and the loop stability. A low ESR capacitor is essential for proper operation. The minimum recommended value is 100μF for most applications, with higher values required for higher current applications.

Inductor Selection

The inductor value determines the ripple current and affects the efficiency. Typical values range from 33μH to 100μH, depending on the input voltage, output voltage, and load current requirements. The inductor must be rated for the peak current (typically 1.3 times the maximum load current).

Thermal Management

Although highly efficient, the LM2670 may require heat sinking in high current applications. The thermal resistance of the package and the maximum expected power dissipation should be considered when designing the PCB layout. Adequate copper area should be provided for surface mount packages.

Conclusion

The LM2670 series provides a complete, high-efficiency step-down switching regulator solution in a single integrated circuit. With its wide input voltage range, high output current capability, and multiple package options, it offers designers a versatile solution for a broad range of power conversion applications. The device's high efficiency minimizes heat dissipation concerns while its simple design requirements (only five external components needed) significantly reduce development time and system cost.