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

8.2.2.4 Input Capacitor Selection

Input capacitors serve two important functions. The first is to reduce input voltage ripple into the LMR60420 and the input filter of the system. The second is to reduce high frequency noise. These two functions are implemented most effectively with separate capacitors. See Table 8-3.

Table 8-3 Input Capacitor
CAPACITORRECOMMENDED VALUECOMMENT
CIN_HF0.1µFThis capacitor is used to suppress high frequency noise originating during switching events. Place the capacitor as close to the LMR60420 devices as design rules allow. Position is more important than exact capacity. After high frequency propagates into a system, suppressing or filtering can be hard. Because this capacitor is exposed to battery voltage in systems that operate directly off of battery, TI recommends 50V or greater rating.
CIN4.7µFThis capacitance is used to suppress input ripple and transients due to output load transients. If CIN is too small, input voltage can dip during load transients resetting the system if the system is operated under low voltage conditions. TI recommends 4.7µF adjacent to the LMR60420 device. Because this capacitor is exposed to battery voltage in systems that operate directly off of battery, TI recommends 50V or greater rating.

The values of CIN_HF and CIN presented in Table 8-3 can be used in most applications. If a certain amount of input voltage ripple is required, Equation 14 can be used to calculate the required input capacitance.

Equation 14. CIN≥D×1-D×IOUT∆VIN_PP×fSW

Where:

  • D = Duty Cycle = VOUT/VIN
  • IOUT = DC output current
  • ΔVIN_PP = peak to peak input voltage ripple
  • fSW = switching frequency

Use Equation 15 to compare the RMS current rating of the selected input capacitors to make sure the input capacitors are capable of supplying the input switching current.

Equation 15. IIN_RMS_max=IOUT×D×1-D+112×VOUTL×fSW×IOUT2×1-D2×D