ZHCSLD0B May   2020  – June 2021 LM62435-Q1

PRODUCTION DATA  

  1. 特性
  2. 应用
  3. 说明
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and Functions
  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 计时特性
    7. 7.7 Systems Characteristics
    8. 7.8 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  EN Uses for Enable and VIN UVLO
      2. 8.3.2  MODE/SYNC Pin Operation
        1. 8.3.2.1 Level-Dependent MODE/SYNC Pin Control
        2. 8.3.2.2 Pulse-Dependent MODE/SYNC Pin Control
        3. 8.3.2.3 Clock Locking
      3. 8.3.3  PGOOD Output Operation
      4. 8.3.4  Internal LDO, VCC UVLO, and BIAS Input
      5. 8.3.5  Bootstrap Voltage and VCBOOT-UVLO (CBOOT Pin)
      6. 8.3.6  Adjustable SW Node Slew Rate
      7. 8.3.7  Spread Spectrum
      8. 8.3.8  Soft Start and Recovery From Dropout
      9. 8.3.9  Output Voltage Setting
      10. 8.3.10 Overcurrent and Short Circuit Protection
      11. 8.3.11 Thermal Shutdown
      12. 8.3.12 Input Supply Current
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
      2. 8.4.2 Standby Mode
      3. 8.4.3 Active Mode
        1. 8.4.3.1 CCM Mode
        2. 8.4.3.2 Auto Mode - Light Load Operation
          1. 8.4.3.2.1 Diode Emulation
          2. 8.4.3.2.2 Frequency Reduction
        3. 8.4.3.3 FPWM Mode - Light Load Operation
        4. 8.4.3.4 Minimum On-time (High Input Voltage) Operation
        5. 8.4.3.5 Dropout
  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  Choosing the Switching Frequency
        2. 9.2.2.2  Setting the Output Voltage
        3. 9.2.2.3  Inductor Selection
        4. 9.2.2.4  Output Capacitor Selection
        5. 9.2.2.5  Input Capacitor Selection
        6. 9.2.2.6  BOOT Capacitor
        7. 9.2.2.7  BOOT Resistor
        8. 9.2.2.8  VCC
        9. 9.2.2.9  BIAS
        10. 9.2.2.10 CFF and RFF Selection
        11. 9.2.2.11 External UVLO
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Ground and Thermal Considerations
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 接收文档更新通知
    3. 12.3 支持资源
    4. 12.4 Trademarks
    5. 12.5 静电放电警告
    6. 12.6 术语表
  13. 13Mechanical, Packaging, and Orderable Information

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机械数据 (封装 | 引脚)
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订购信息

Power Supply Recommendations

The characteristics of the input supply must be compatible with Absolute Maximum Ratings and Recommended Operating Conditions in this data sheet. In addition, the input supply must be capable of delivering the required input current to the loaded converter. The average input current can be estimated with Equation 13.

Equation 13. GUID-9D7F4F53-FC85-4809-A1C7-63066F5C5856-low.gif

where

  • η is the efficiency

If the converter is connected to the input supply through long wires or PCB traces, special care is required to achieve good performance. The parasitic inductance and resistance of the input cables can have an adverse effect on the operation of the converter. The parasitic inductance, in combination with the low-ESR, ceramic input capacitors, can form an under-damped resonant circuit, resulting in overvoltage transients at the input to the converter or tripping UVLO. The parasitic resistance can cause the voltage at the VIN pin to dip whenever a load transient is applied to the output. If the application is operating close to the minimum input voltage, this dip can cause the converter to momentarily shutdown and reset. The best way to solve these kind of issues is to reduce the distance from the input supply to the converter and use an aluminum input capacitor in parallel with the ceramics. The moderate ESR of this type of capacitor helps damp the input resonant circuit and reduce any overshoot or undershoot at the input. A value in the range of 20 µF to 100 µF is usually sufficient to provide input damping and help hold the input voltage steady during large load transients.

In some cases, a transient voltage suppressor (TVS) is used on the input of converters. One class of this device has a snap-back characteristic (thyristor type). The use of a device with this type of characteristic is not recommended. When the TVS fires, the clamping voltage falls to a very low value. If this voltage is less than the output voltage of the converter, the output capacitors discharge through the device back to the input. This uncontrolled current flow can damage the TVS and cause large input transients.

The input voltage must not be allowed to fall below the output voltage. In this scenario, such as a shorted input test, the output capacitors discharge through the internal parasitic diode found between the VIN and SW pins of the device. During this condition, the current can become uncontrolled, possibly causing damage to the device. If this scenario is considered likely, then a Schottky diode between the input supply and the output must be used.