SNVSAR5B December   2016  – March 2018 LMR23625-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
      2.      Efficiency vs Load, VIN = 12 V, PFM Option
  4. 4 Revision History
  5. 5 Device Comparison
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 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 Characteristics
    7. 7.7 Switching Characteristics
    8. 7.8 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Fixed-Frequency Peak-Current-Mode Control
      2. 8.3.2  Adjustable Output Voltage
      3. 8.3.3  EN/SYNC
      4. 8.3.4  VCC, UVLO
      5. 8.3.5  Minimum ON-Time, Minimum OFF-Time and Frequency Foldback at Dropout Conditions
      6. 8.3.6  Power Good (PGOOD)
      7. 8.3.7  Internal Compensation and CFF
      8. 8.3.8  Bootstrap Voltage (BOOT)
      9. 8.3.9  Overcurrent and Short-Circuit Protection
      10. 8.3.10 Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
      2. 8.4.2 Active Mode
      3. 8.4.3 CCM Mode
      4. 8.4.4 Light Load Operation (PFM Option)
      5. 8.4.5 Light Load Operation (FPWM Option)
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1  Custom Design With WEBENCH® Tools
        2. 9.2.2.2  Output Voltage Setpoint
        3. 9.2.2.3  Switching Frequency
        4. 9.2.2.4  Inductor Selection
        5. 9.2.2.5  Output Capacitor Selection
        6. 9.2.2.6  Feed-Forward Capacitor
        7. 9.2.2.7  Input Capacitor Selection
        8. 9.2.2.8  Bootstrap Capacitor Selection
        9. 9.2.2.9  VCC Capacitor Selection
        10. 9.2.2.10 Undervoltage Lockout Setpoint
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Compact Layout for EMI Reduction
      2. 11.1.2 Ground Plane and Thermal Considerations
      3. 11.1.3 Feedback Resistors
    2. 11.2 Layout Examples
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Development Support
        1. 12.1.1.1 Custom Design With WEBENCH® Tools
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • DRR|12
  • DDA|8
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9.2.2.6 Feed-Forward Capacitor

The LMR23625-Q1 is internally compensated. Depending on the VOUT and frequency fSW, if the output capacitor COUT is dominated by low ESR (ceramic types) capacitors, it could result in low phase margin. To improve the phase boost an external feed-forward capacitor CFF can be added in parallel with RFBT. Choose CFF is so that phase margin is boosted at the crossover frequency without CFF. A simple estimation for the crossover frequency (fX) without CFF is shown in Equation 17, assuming COUT has very small ESR, and COUT value is after derating.

Equation 17. LMR23625-Q1 equation_14_snvsah2.gif

Equation 18 for CFF was tested:

Equation 18. LMR23625-Q1 equation_15_snvsah2.gif

For designs with higher ESR, CFF is not needed when COUT has very high ESR; reduce CFF calculated from Equation 18 with medium ESR. Table 2 can be used as a quick starting point.

For the application in this design example, a 18-pF, 50-V COG capacitor is selected.