JAJSBZ4B June   2014  – January 2018 LM46001


  1. 特長
  2. アプリケーション
  3. 概要
    1.     Device Images
      1.      概略回路図
      2.      放射エミッションのグラフ VOUT = 3.3V、VIN = 24V、FS= 500kHz、IOUT = 1A
  4. 改訂履歴
  5. Pin Configuration and Functions
    1.     Pin Functions
  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. 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 Controlled Step-Down Regulator
      2. 7.3.2  Light Load Operation
      3. 7.3.3  Adjustable Output Voltage
      4. 7.3.4  Enable (ENABLE)
      5. 7.3.5  VCC, UVLO, and BIAS
      6. 7.3.6  Soft-Start and Voltage Tracking (SS/TRK)
      7. 7.3.7  Switching Frequency (RT) and Synchronization (SYNC)
      8. 7.3.8  Minimum ON-Time, Minimum OFF-Time and Frequency Foldback at Dropout Conditions
      9. 7.3.9  Internal Compensation and CFF
      10. 7.3.10 Bootstrap Voltage (CBOOT)
      11. 7.3.11 Power Good (PGOOD)
      12. 7.3.12 Overcurrent and Short-Circuit Protection
      13. 7.3.13 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Stand-by Mode
      3. 7.4.3 Active Mode
      4. 7.4.4 CCM Mode
      5. 7.4.5 Light Load Operation
      6. 7.4.6 Self-Bias Mode
  8. Applications 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.  Custom Design With WEBENCH® Tools
        2.  Output Voltage Setpoint
        3.  Switching Frequency
        4.  Input Capacitors
        5.  Inductor Selection
        6.  Output Capacitor Selection
        7.  Feed-Forward Capacitor
        8.  Bootstrap Capacitors
        9.  VCC Capacitor
        10. BIAS Capacitors
        11. Soft-Start Capacitors
        12. Undervoltage Lockout Setpoint
        13. PGOOD
      3. 8.2.3 Application Curves
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Compact Layout for EMI Reduction
      2. 10.1.2 Ground Plane and Thermal Considerations
      3. 10.1.3 Feedback Resistors
    2. 10.2 Layout Example
  11. 11デバイスおよびドキュメントのサポート
    1. 11.1 デバイス・サポート
      1. 11.1.1 開発サポート
        1. WEBENCH®ツールによるカスタム設計
    2. 11.2 ドキュメントの更新通知を受け取る方法
    3. 11.3 コミュニティ・リソース
    4. 11.4 商標
    5. 11.5 静電気放電に関する注意事項
    6. 11.6 Glossary
  12. 12メカニカル、パッケージ、および注文情報



Overcurrent and Short-Circuit Protection

The LM46001 is protected from overcurrent conditions by cycle-by-cycle current limiting on both peak and valley of the inductor current. Hiccup mode is activated to prevent overheating if a fault condition persists.

High-side MOSFET overcurrent protection is implemented by the nature of the peak current mode control. The HS switch current is sensed when the HS is turned on after a set blanking time. The HS switch current is compared to the output of the error amplifier (EA) minus slope compensation every switching cycle. See Functional Block Diagram for more details. The peak current of the HS switch is limited by the maximum EA output voltage minus the slope compensation at every switching cycle. The slope compensation magnitude at the peak current is proportional to the duty cycle.

When the LS switch is turned on, the current going through it is also sensed and monitored. The LS switch is turned OFF at the end of a switching cycle if its current is above the LS current limit ILS-LIMIT. The LS switch is kept ON so that inductor current keeps ramping down, until the inductor current ramps below ILS-LIMIT. Then the LS switch is turned OFF, and the HS switch is turned on after a dead time. If the current of the LS switch is higher than the LS current limit for 32 consecutive cycles and the power-good flag is low, hiccup current protection mode is activated. In hiccup mode, the regulator is shut down and kept off for 5.5 ms typically before the LM46001 tries to start again. If over-current or short-circuit fault condition still exist, hiccup repeats until the fault condition is removed. Hiccup mode reduces power dissipation under severe over-current conditions, preventing over heating and potential damage to the device.

Hiccup is only activated when the power-good flag is low. Under non-severe overcurrent conditions when VOUT has not fallen outside of the PGOOD tolerance band, the LM46001 reduces the switching frequency and keep the inductor current valley clamped at the LS current limit level. This operation mode allows slight over current operation during load transients without tripping hiccup. If the power-good flag becomes low, hiccup operation starts after LS current limit is tripped 32 consecutive cycles.