SNVS639G December   2009  – December 2015 LM21305

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Synchronous DC-DC Switching Converter
      2. 8.3.2  Peak Current-Mode Control
      3. 8.3.3  Switching Frequency Setting and Synchronization
      4. 8.3.4  Light-Load Operation
      5. 8.3.5  Precision Enable
      6. 8.3.6  Device Enable, Soft-Start, and Pre-Bias Startup Capability
      7. 8.3.7  Peak Current Protection and Negative Current Limiting
      8. 8.3.8  PGOOD Indicator
      9. 8.3.9  Internal Bias Regulators
      10. 8.3.10 Minimum On-Time Considerations
    4. 8.4 Device Functional Modes
      1. 8.4.1 Overvoltage and Undervoltage Handling
      2. 8.4.2 Undervoltage Lockout (UVLO)
      3. 8.4.3 Thermal Protection
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1  Setting the Output Voltage
        2. 9.2.2.2  Calculating the Duty Cycle
        3. 9.2.2.3  Input Capacitors
        4. 9.2.2.4  AVIN Filter
        5. 9.2.2.5  Switching Frequency Selection
        6. 9.2.2.6  Filter Inductor
        7. 9.2.2.7  Output Capacitor
        8. 9.2.2.8  Efficiency Considerations
        9. 9.2.2.9  Load Current Derating When Duty Cycle Exceeds 50%
        10. 9.2.2.10 Control Loop Compensation
        11. 9.2.2.11 Compensation Components Selection
        12. 9.2.2.12 Plotting the Loop Gain
        13. 9.2.2.13 High Frequency Considerations
        14. 9.2.2.14 Bootstrap Capacitor
        15. 9.2.2.15 5V0 and 2V5 Capacitors
        16. 9.2.2.16 Maximum Ambient Temperature
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Compact PCB Layout for EMI Reduction
      2. 11.1.2 Ground Plane and Thermal Design Considerations
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Development Support
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
      2. 12.2.2 PCB Layout Resources
      3. 12.2.3 Resources for Thermal PCB Design
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

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1 Features

  • High-Efficiency Synchronous DC-DC Converter:
    • Integrated Low RDSon Power MOSFETs
    • Wide Input Voltage Range: 3 V to 18 V
    • Load Current as High as 5 A
    • Switching Frequency: 300 kHz to 1.5 MHz
  • External Frequency Synchronization
  • Accurate 0.598-V Feedback Voltage Reference
  • Ultra-Fast Line and Load Transient Response:
    • Peak Current-Mode Control
    • Internal Slope Compensation
    • High-Bandwidth Error Amplifier
  • Ultra-Low Shutdown Quiescent Current
  • Wide Duty-Cycle Operating Range:
    • TON-MIN: 70 ns for Low VOUT
    • TOFF-MIN: 50 ns for High Duty Cycle
  • Diode Emulation Mode at Light Loads
  • Integrated Bias Supply LDO Sub-Regulators
  • Internal Soft-Start Function:
    • Monotonic Startup into Pre-Biased Loads
  • Precision Enable Input with Hysteresis
  • Open-Drain PGOOD Indicator
  • Internal Input Undervoltage Lockout (UVLO)
  • Cycle-by-Cycle Overcurrent Protection
  • Output Overvoltage Protection (OVP)
  • Thermal Shutdown Protection with Hysteresis
  • 5-mm x 5-mm WQFN-28 PowerPAD™ Package

2 Applications

  • DC-DC Converters and POL Modules
  • DSP and FPGA Core Voltage Supplies
  • Telecommunications Infrastructure
  • Embedded Computing, Servers, and Storage

3 Description

The LM21305 is a full-featured, 5-A, synchronous buck dc-dc converter optimized for solution size, flexibility, and high conversion efficiency. High-power density LM21305 designs are easily achieved by virtue of monolithic integration of high-side and low-side power MOSFETs, high switching frequency, peak current-mode control, and optimized thermal design. The efficiency of the LM21305 is maximized at light loads with diode emulation mode operation and at heavy loads by optimal design of the MOSFET adaptive gate drivers to minimize switch dead-times and body-diode conduction losses.

The LM21305 accepts a wide input voltage range of 3 V to 18 V for interface to various intermediate bus voltages, including 3.3-V, 5-V, and 12-V rails. A 1.5% voltage reference and 70-ns, high-side MOSFET minimum controllable on-time enable output voltages as low as 0.598 V with excellent setpoint accuracy. The LM21305 is available in a 5-mm × 5-mm2 WQFN-28 thermally-enhanced package with 0.5-mm pitch.

Device Information(1)

PART NUMBER PACKAGE BODY SIZE (NOM)
LM21305 WQFN (28) 5.00 mm × 5.00 mm
  1. For all available packages, see the orderable addendum at the end of the data sheet.

Typical Application Circuit

LM21305 Typ_app_schematic_nvs639.gif

Typical Efficiency at 12 V, 500 kHz

LM21305 30111153.gif