JAJSFZ2E August   2012  – September 2021 LMZ20501

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
  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 System Characteristics
    7. 6.7 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 Nano Scale Package
      2. 7.3.2 Internal Synchronous Rectifier
      3. 7.3.3 Current Limit Protection
      4. 7.3.4 Start-Up
      5. 7.3.5 Dropout Behavior
      6. 7.3.6 Power Good Flag Function
      7. 7.3.7 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 PWM Operation
      2. 7.4.2 PFM Operation
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Detailed Design Procedure
        1. 8.2.1.1 Custom Design With WEBENCH® Tools
        2. 8.2.1.2 Setting The Output Voltage
        3. 8.2.1.3 Output and Feedforward Capacitors
        4. 8.2.1.4 Input Capacitors
        5. 8.2.1.5 Maximum Ambient Temperature
        6. 8.2.1.6 Options
      2. 8.2.2 Application Curves
    3. 8.3 Do's and Don'ts
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
      1. 10.2.1 Soldering Information
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
      2. 11.1.2 Development Support
        1. 11.1.2.1 Custom Design With WEBENCH® Tools
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 サポート・リソース
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information
    1. 12.1 Tape and Reel Information

パッケージ・オプション

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発注情報

7.3.5 Dropout Behavior

When the input voltage is close to the output voltage, the regulator will operate at very large duty cycles. Normal time delays of the internal circuits prevents the attainment of controlled duty cycles near 100%. In this condition, the LMZ20501 will skip switching cycles to maintain regulation with the highest possible input-to-output ratio. Some increase in output voltage ripple can appear as the regulator skips cycles. As the input voltage gets closer to the output voltage, the regulator will eventually reach 100% duty cycle, with the high side switch turned on. The output will then follow the input voltage minus the drop across the high-side switch and inductor resistance. Figure 7-5 and Figure 7-6 show typical dropout behavior for output voltages of 2.5 V and 3.3 V.

Since the internal gate drive levels of the LMZ20501 are dependent on input voltage, the Rdson of the power FETs will increase at low input voltages. This will result in degraded efficiency at input voltages below approximately 2.9 V. Also, combinations of low input voltage and high output voltage increase the effective switch duty cycle, which can result in increased output voltage ripple.

GUID-0A15D9D7-A4A6-4E8D-BC34-A8EE1C467168-low.pngFigure 7-5 Typical Dropout Behavior, VOUT = 2.5 V
GUID-35FC7B2E-04B5-4C12-AD1D-08F2AB915BB7-low.pngFigure 7-6 Typical Dropout Behavior, VOUT = 3.3 V