ZHCSJO3 May   2019 LMR34215-Q1

PRODUCTION DATA.  

  1. 特性
  2. 应用
  3. 说明
    1. 3.1 简化原理图
  4. 修订历史记录
  5. Device Comparison Table
  6. Pin Configuration and Functions
    1. Table 1. Pin 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 Timing Requirements
    7. 7.7 System 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 Power-Good Flag Output
      2. 8.3.2 Enable and Start-up
      3. 8.3.3 Current Limit and Short Circuit
      4. 8.3.4 Undervoltage Lockout and Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Auto Mode
      2. 8.4.2 Forced PWM Operation
      3. 8.4.3 Dropout
      4. 8.4.4 Minimum Switch On-Time
      5. 8.4.5 Spread Spectrum Operation
  9. Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
        1. 9.2.1.1 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
          1. 9.2.2.2.1 FB for Adjustable Output
        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  CBOOT
        7. 9.2.2.7  VCC
        8. 9.2.2.8  CFF Selection
        9. 9.2.2.9  External UVLO
        10. 9.2.2.10 Maximum Ambient Temperature
      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. 12器件和文档支持
    1. 12.1 器件支持
      1. 12.1.1 开发支持
    2. 12.2 文档支持
      1. 12.2.1 相关文档
    3. 12.3 接收文档更新通知
    4. 12.4 社区资源
    5. 12.5 商标
    6. 12.6 静电放电警告
    7. 12.7 Glossary
  13. 13机械、封装和可订购信息

封装选项

机械数据 (封装 | 引脚)
散热焊盘机械数据 (封装 | 引脚)
订购信息

Enable and Start-up

Start-up and shutdown are controlled by the EN input. This input features precision thresholds, allowing the use of an external voltage divider to provide an adjustable input UVLO (see the External UVLO section). Applying a voltage of ≥ VEN-VCC-H causes the device to enter standby mode, powering the internal VCC, but not producing an output voltage. Increasing the EN voltage to VEN-OUT-H (VEN-H in Figure 10) fully enables the device, allowing it to enter start-up mode and beginning the soft-start period. When the EN input is brought below VEN-OUT-H (VEN-H in Figure 10) by VEN-OUT-HYS (VEN-HYS in Figure 10), the regulator stops running and enters standby mode. Further decrease in the EN voltage to below VEN-VCC-L completely shuts down the device. This behavior is shown in Figure 10. The EN input may be connected directly to VIN if this feature is not needed. This input must not be allowed to float. The values for the various EN thresholds can be found in the Electrical Characteristics table.

The LMR34215-Q1 utilizes a reference-based soft start that prevents output voltage overshoots and large inrush currents as the regulator is starting up. A typical start-up waveform is shown in Figure 11 along with typical timings. The rise time of the output voltage is about 4 ms.

LMR34215-Q1 LMR360XX-EN-threshold-plot-snvsay7.gifFigure 10. Precision Enable Behavior
LMR34215-Q1 waveform-05-LMR36015FSC-12VIN-5VOUT-STARTUP-SNVSAY8.jpgFigure 11. Typical Start-up Behavior
VIN = 12V, VOUT = 5 V, IOUT = 1.5 A