SNAS879 December   2024 LMR60420

PRODMIX  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and Functions
  7. 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 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Enable and Undervoltage Lockout (UVLO)
      2. 7.3.2 Soft Start and Recovery from Dropout
      3. 7.3.3 Frequency Selection With RT
      4. 7.3.4 MODE/SYNC Pin Control
      5. 7.3.5 Output Voltage Selection
      6. 7.3.6 Current Limit
      7. 7.3.7 Hiccup Mode
      8. 7.3.8 Power-Good Function
      9. 7.3.9 Spread Spectrum
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown
      2. 7.4.2 Active Mode
        1. 7.4.2.1 Continuous Conduction Mode (CCM)
        2. 7.4.2.2 Auto Mode - Light Load Operation
        3. 7.4.2.3 FPWM Operation - Light Load Operation
        4. 7.4.2.4 Minimum On-Time
        5. 7.4.2.5 Dropout
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Switching Frequency Selection
        2. 8.2.2.2 Inductor Selection
        3. 8.2.2.3 Output Capacitor Selection
        4. 8.2.2.4 Input Capacitor Selection
        5. 8.2.2.5 Bootstrap Capacitor (CBOOT) Selection
        6. 8.2.2.6 FB Voltage Divider for Adjustable Output Voltages
          1. 8.2.2.6.1 Feedforward Capacitor (CFF) Selection
        7. 8.2.2.7 RPG - PG Pullup Resistor
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
        1. 8.4.1.1 Ground and Thermal Plane Considerations
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

7.3.1 Enable and Undervoltage Lockout (UVLO)

LMR60420 features a precision enable and undervoltage lockout (UVLO) feature which enables the user to select the voltage level at which the device powers on and off based on the voltage present at the EN pin. To power on the device the voltage between EN pin and PGND pin must exceed the enable voltage rising threshold VEN-TH(R) (1.25V typical). After VEN-TH(R) has been crossed, and the minimum supply voltage, VINUVLO(R), have both been satisfied, the part begins the soft-start sequence described in Section 7.3.2.

The EN pin can be used to power down the device by reducing the voltage between the EN pin and PGND pin below the enable input low threshold VEN-TH(F) 1V (typical).

A resistor divider between VIN and PGND with the center point connected to the EN pin can be used to implement the VIN UVLO. To begin, select the input voltage at which the device turns off, choose the value of RENT, then calculate the required RENB. After RENB has been calculated, the resulting turn-on input voltage can be calculated. See Figure 7-1, Equation 1, and Equation 2 to determine the EN resistors required. If the VIN UVLO feature is not needed, the EN pin can be connected directly to VIN.

Equation 1. R E N B = V E N - T H ( F ) V I N t u r n - o f f - V E N - T H ( F ) × R E N T
Equation 2. V I N t u r n - o n = 1 + R E N T R E N B × V E N - T H ( R )

Where:

  • VINturn-off represents the input voltage at which the LMR60420 turns off.
  • VINturn-on represents the input voltage at which the LMR60420 turns on.

LMR60420 VIN UVLO Using the EN Pin Figure 7-1 VIN UVLO Using the EN Pin