ZHCS529I January   2007  – April 2025 LM25574

PRODUCTION DATA  

  1.   1
  2. 1 特性
  3. 2 应用
  4. 3 说明
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 High Voltage Start-Up Regulator
    4. 6.4 Device Functional Modes
      1. 6.4.1 Shutdown and Standby Mode
      2. 6.4.2 Oscillator and Sync Capability
      3. 6.4.3 Error Amplifier and PWM Comparator
      4. 6.4.4 Ramp Generator
      5. 6.4.5 Maximum Duty Cycle and Input Drop-out Voltage
      6. 6.4.6 Current Limit
      7. 6.4.7 Soft-Start
      8. 6.4.8 Boost Pin
      9. 6.4.9 Thermal Protection
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Typical Schematic for High Frequency (1MHz) Application
      2. 7.2.2 Design Requirements
      3. 7.2.3 Detailed Design Procedure
        1. 7.2.3.1  Custom Design With WEBENCH® Tools
        2. 7.2.3.2  External Components
        3. 7.2.3.3  R3 -RT Resistor
        4. 7.2.3.4  L1-Inductor
        5. 7.2.3.5  C3 (CRAMP)
        6. 7.2.3.6  C9-Output Capacitor
        7. 7.2.3.7  C1-Input Capacitor
        8. 7.2.3.8  C8- VCC Capacitor
        9. 7.2.3.9  C7- BST capacitor
        10. 7.2.3.10 C4 - SS Capacitor
        11. 7.2.3.11 R5, R6 - Feedback Resistor
        12. 7.2.3.12 R1, R2, C2 - SD Pin Components
        13. 7.2.3.13 R4, C5, C6 - Compensation Components
        14. 7.2.3.14 Bias Power Dissipation Reduction
      4. 7.2.4 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
        1. 7.4.1.1 PCB Layout and Thermal Considerations
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Developmental Support
        1. 8.1.1.1 Custom Design With WEBENCH® Tools
    2. 8.2 接收文档更新通知
    3. 8.3 支持资源
    4. 8.4 Trademarks
    5. 8.5 静电放电警告
    6. 8.6 术语表
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

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7.2.3.7 C1-Input Capacitor

The regulator supply voltage has a large source impedance at the switching frequency. Good quality input capacitors are necessary to limit the ripple voltage at the VIN pin while supplying most of the switch current during the on-time. When the buck switch turns on, the current into the VIN pin steps to the lower peak of the inductor current waveform, ramps up to the peak value, then drops to zero at turn-off. The average current into VIN during the on-time is the load current. The input capacitance must be selected for RMS current rating and minimum ripple voltage. A good approximation for the required ripple current rating necessary is IRMS > IOUT / 2.

Quality ceramic capacitors with a low ESR must be selected for the input filter. To allow for capacitor tolerances and voltage effects, one 1.0 µF, 100 V ceramic capacitor is used. If step input voltage transients are expected near the maximum rating of the LM25574, a careful evaluation of ringing and possible spikes at the device VIN pin must be completed. An additional damping network or input voltage clamp can be required in these cases.