JAJSEV5E February   2018  – July 2020 LMR23625

PRODUCTION DATA  

  1. 1 特長
  2. 2 アプリケーション
  3. 3 概要
  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 Timing Requirements
    7. 6.7 Switching Characteristics
    8. 6.8 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 Fixed-Frequency Peak-Current-Mode Control
      2. 7.3.2 Adjustable Output Voltage
      3. 7.3.3 Enable/Sync
      4. 7.3.4 VCC, UVLO
      5. 7.3.5 Minimum ON-time, Minimum OFF-time and Frequency Foldback at Drop-out Conditions
      6. 7.3.6 Internal Compensation and CFF
      7. 7.3.7 Bootstrap Voltage (BOOT)
      8. 7.3.8 Overcurrent and Short-Circuit Protection
      9. 7.3.9 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Active Mode
      3. 7.4.3 CCM Mode
      4. 7.4.4 Light Load Operation (PFM Option)
      5. 7.4.5 Light Load Operation (FPWM Option)
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  Custom Design With WEBENCH® Tools
        2. 8.2.2.2  Output Voltage Setpoint
        3. 8.2.2.3  Switching Frequency
        4. 8.2.2.4  Inductor Selection
        5. 8.2.2.5  Output Capacitor Selection
        6. 8.2.2.6  Feed-forward Capacitor
        7. 8.2.2.7  Input Capacitor Selection
        8. 8.2.2.8  Bootstrap Capacitor Selection
        9. 8.2.2.9  VCC Capacitor Selection
        10. 8.2.2.10 Undervoltage Lockout Set-Point
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Compact Layout for EMI Reduction
    4. 10.4 Ground Plane and Thermal Considerations
    5. 10.5 Feedback Resistors
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
        1. 11.1.1.1 Custom Design With WEBENCH® Tools
    2. 11.2 ドキュメントの更新通知を受け取る方法
    3. 11.3 サポート・リソース
    4. 11.4 Trademarks
    5. 11.5 静電気放電に関する注意事項
    6. 11.6 用語集
  12. 12Mechanical, Packaging, and Orderable Information

パッケージ・オプション

デバイスごとのパッケージ図は、PDF版データシートをご参照ください。

メカニカル・データ（パッケージ｜ピン）
  • DDA|8
  • DRR|12
サーマルパッド・メカニカル・データ
発注情報

8.2.2.4 Inductor Selection

The most critical parameters for the inductor are the inductance, saturation current, and the rated current. The inductance is based on the desired peak-to-peak ripple current ΔiL. Because the ripple current increases with the input voltage, the maximum input voltage is always used to calculate the minimum inductance LMIN. Use Equation 12 to calculate the minimum value of the output inductor. KIND is a coefficient that represents the amount of inductor ripple current relative to the maximum output current of the device. A reasonable value of KIND must be 20% to 40%. During an instantaneous short or over current operation event, the RMS and peak inductor current can be high. The inductor current rating must be higher than the current limit of the device.

Equation 11. GUID-1FCE5797-00E4-488C-B971-FC7307A1446E-low.gif
Equation 12. GUID-E181FC69-C5A4-43A4-BB17-AED42501EFE2-low.gif

In general, it is preferable to choose lower inductance in switching power supplies, because it usually corresponds to faster transient response, smaller DCR, and reduced size for more compact designs. However, inductance that is too low can generate an inductor current ripple that is too high so that overcurrent protection at the full load may be falsely triggered. It also generates more conduction loss and inductor core loss. Larger inductor current ripple also implies larger output voltage ripple with same output capacitors. With peak-current-mode control, TI does not recommend having an inductor current ripple that is too small. A larger peak current ripple improves the comparator signal-to-noise ratio.

For this design example, choose KIND = 0.4, the minimum inductor value is calculated to be 1.9 µH. Choose the nearest standard 2.2 μH ferrite inductor with a capability of 3.5-A RMS current and 6-A saturation current.