SNVS480J January   2007  – July 2020 LM5022

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Application
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 High-Voltage Start-Up Regulator
      2. 7.3.2 Input Undervoltage Detector
      3. 7.3.3 Error Amplifier
      4. 7.3.4 Current Sensing and Current Limiting
      5. 7.3.5 PWM Comparator and Slope Compensation
      6. 7.3.6 Soft Start
      7. 7.3.7 MOSFET Gate Driver
      8. 7.3.8 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Oscillator, Shutdown, and SYNC
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  Switching Frequency
        2. 8.2.2.2  MOSFET
        3. 8.2.2.3  Output Diode
        4. 8.2.2.4  Boost Inductor
        5. 8.2.2.5  Output Capacitor
        6. 8.2.2.6  VCC Decoupling Capacitor
        7. 8.2.2.7  Input Capacitor
        8. 8.2.2.8  Current Sense Filter
        9. 8.2.2.9  RSNS, RS2, and Current Limit
        10. 8.2.2.10 Control Loop Compensation
        11. 8.2.2.11 Efficiency Calculations
          1. 8.2.2.11.1 Chip Operating Loss
          2. 8.2.2.11.2 MOSFET Switching Loss
          3. 8.2.2.11.3 MOSFET and RSNS Conduction Loss
          4. 8.2.2.11.4 Output Diode Loss
          5. 8.2.2.11.5 Input Capacitor Loss
          6. 8.2.2.11.6 Output Capacitor Loss
          7. 8.2.2.11.7 Boost Inductor Loss
          8. 8.2.2.11.8 Total Loss
          9. 8.2.2.11.9 Efficiency
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Filter Capacitors
      2. 10.1.2 Sense Lines
      3. 10.1.3 Compact Layout
      4. 10.1.4 Ground Plane and Shape Routing
    2. 10.2 Layout Examples
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
      2. 11.1.2 Development Support
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Support Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.2.2.3 Output Diode

The boost regulator requires an output diode D1 (see Figure 14) to carrying the inductor current during the MOSFET off-time. The most efficient choice for D1 is a Schottky diode due to low forward drop and near-zero reverse recovery time. D1 must be rated to handle the maximum output voltage plus any switching node ringing when the MOSFET is on. In practice, all switching converters have some ringing at the switching node due to the diode parasitic capacitance and the lead inductance. D1 must also be rated to handle the average output current, IO.

The overall converter efficiency becomes more dependent on the selection of D1 at low duty cycles, where the boost diode carries the load current for an increasing percentage of the time. This power dissipation can be calculating by checking the typical diode forward voltage, VD, from the I-V curve on the data sheet of the diode and then multiplying it by IO. Diode data sheets also provides a typical junction-to-ambient thermal resistance, RθJA, which can be used to estimate the operating die temperature of the Schottky. Multiplying the power dissipation (PD = IO × VD) by RθJA gives the temperature rise. The diode case size can then be selected to maintain the Schottky diode temperature below the operational maximum.

In this example, a Schottky diode rated to 60 V and 1 A is suitable, as the maximum diode current is 0.5 A. A small case such as SOD-123 can be used if a small footprint is critical. Larger case sizes generally have lower RθJA and lower forward voltage drop, so for better efficiency the larger SMA case size is used.