LM2621 High Efficiency Step-Up DC-DC Switching Regulator

Overview

The LM2621 is a high-efficiency, step-up DC-DC switching regulator specifically designed for battery-powered and low input voltage systems. This advanced regulator accepts a wide input voltage range from 1.2V to 14V and efficiently converts it to a regulated output voltage adjustable between 1.24V and 14V. The device incorporates an internal 0.17Ω N-Channel MOSFET power switch, enabling efficiencies of up to 90% in typical applications.

Utilizing a unique constant-duty-cycle gated oscillator topology, the LM2621 maintains high efficiency across a broad load range. Its high switching frequency (adjustable up to 2MHz) allows for the use of compact surface mount inductors and capacitors, making it ideal for space-constrained applications. The BiCMOS process technology reduces supply current to just 80µA, while shutdown mode further minimizes power consumption.

Key Features

• Wide input voltage range: 1.2V to 14V
• Adjustable output voltage: 1.24V to 14V
• High efficiency up to 90%
• Internal 0.17Ω N-Channel MOSFET power switch
• Adjustable switching frequency up to 2MHz
• Low supply current: 80µA typical
• Ultra-low shutdown current: 0.01µA typical
• Small Mini-SO8 package (half the footprint of standard 8-pin SO package)
• Thermal shutdown protection
• Current limit protection
• Soft-start capability

Applications

The LM2621 is ideally suited for a variety of portable and battery-powered applications, including:

• Battery backup systems
• Portable medical devices
• Handheld instruments
• Digital cameras and camcorders
• Wireless communication devices
• PDAs and portable computing devices
• Solar-powered systems
• White LED drivers
• Low-voltage power supplies

Electrical Characteristics

Absolute Maximum Ratings

• Input Voltage (VIN): -0.3V to 15V
• Feedback Voltage (VFB): -0.3V to 15V
• Switch Voltage (VSW): -0.3V to 20V
• Operating Junction Temperature: -40°C to +125°C
• Storage Temperature: -65°C to +150°C

Recommended Operating Conditions

• Input Voltage Range: 1.2V to 14V
• Output Voltage Range: 1.24V to 14V
• Operating Temperature Range: -40°C to +85°C
• Switching Frequency Range: 300kHz to 2MHz

Typical Performance Characteristics

• Start-up Voltage: 1.2V (typical)
• Feedback Voltage: 1.24V ±2%
• Switch Current Limit: 1.5A (typical)
• Quiescent Current: 80µA (typical)
• Shutdown Current: 0.01µA (typical)
• Efficiency: Up to 90% (depending on configuration)

Package Information

Mini-SO8 Package Details

The LM2621 is available in a space-saving Mini-SO8 package that occupies half the footprint of a standard 8-pin SO package. This compact form factor makes it particularly suitable for portable and space-constrained applications.

• Package Dimensions: 3mm × 3mm (body)
• Lead Pitch: 0.65mm
• Package Height: 1.1mm (maximum)
• Lead Count: 8
• Termination: Matte Tin (Sn)
• Moisture Sensitivity Level (MSL): 1 (unlimited floor life at ≤30°C/85% RH)

Pin Configuration

• Pin 1 (FB): Feedback input for output voltage regulation
• Pin 2 (GND): Ground reference
• Pin 3 (COMP): Compensation node for frequency control
• Pin 4 (SHDN): Shutdown control input (active low)
• Pin 5 (VCC): Regulator supply voltage
• Pin 6 (SW): Switch node connection to inductor
• Pin 7 (NC): No connection
• Pin 8 (VIN): Input voltage supply

Design Considerations

Inductor Selection

For optimal performance, select an inductor with:

• Low DC resistance to minimize power loss
• Saturation current rating higher than the peak switch current
• Inductance value between 4.7µH to 22µH for most applications
• Shielded construction to reduce EMI

Output Capacitor Selection

Recommended characteristics include:

• Low ESR for better efficiency and output ripple
• Ceramic capacitors preferred for most applications
• Minimum capacitance of 10µF for stable operation
• Voltage rating at least 1.5 times the output voltage

Input Capacitor Selection

Key considerations:

• Place as close as possible to the VIN and GND pins
• Low ESR ceramic capacitor recommended
• Typical value of 10µF for most applications
• Additional bulk capacitance may be needed for battery inputs

Thermal Considerations

The LM2621 features thermal shutdown protection that activates at approximately 150°C. For optimal thermal performance:

• Ensure adequate PCB copper area for heat dissipation
• Use thermal vias when possible
• Monitor junction temperature in high ambient temperature applications
• Consider forced air cooling for high power applications

Conclusion

The LM2621 represents an excellent solution for applications requiring efficient step-up voltage conversion from low input voltages. Its combination of high efficiency, wide input voltage range, and compact package size makes it particularly suitable for battery-powered portable devices. The adjustable switching frequency allows designers to optimize for either efficiency or component size, while the comprehensive protection features ensure reliable operation under various conditions.

When implementing the LM2621, careful attention should be paid to component selection, PCB layout, and thermal management to achieve optimal performance. Following the manufacturer's recommended design guidelines will help ensure stable operation and maximize the efficiency benefits of this advanced switching regulator.