SNVSAU0 March   2017 LM5141

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin 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 Switching 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  High Voltage Start-up Regulator
      2. 7.3.2  VCC Regulator
      3. 7.3.3  Oscillator
      4. 7.3.4  Synchronization
      5. 7.3.5  Frequency Dithering (Spread Spectrum)
      6. 7.3.6  Enable
      7. 7.3.7  Power Good
      8. 7.3.8  Output Voltage
        1. 7.3.8.1 Minimum Output Voltage Adjustment
      9. 7.3.9  Current Sense
      10. 7.3.10 DCR Current Sensing
      11. 7.3.11 Error Amplifier and PWM Comparator
      12. 7.3.12 Slope Compensation
      13. 7.3.13 Hiccup Mode Current Limiting
      14. 7.3.14 Standby Mode
      15. 7.3.15 Soft-Start
      16. 7.3.16 Diode Emulation
      17. 7.3.17 High and Low Side Drivers
  8. 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 Custom Design With WEBENCH® Tools
      3. 8.2.3 Inductor Calculation
      4. 8.2.4 Current Sense Resistor
      5. 8.2.5 Output Capacitor
      6. 8.2.6 Input Filter
        1. 8.2.6.1 EMI Filter Design
        2. 8.2.6.2 MOSFET Selection
        3. 8.2.6.3 Driver Slew Rate Control
        4. 8.2.6.4 Frequency Dithering
      7. 8.2.7 8.9 Control Loop
        1. 8.2.7.1 Feedback Compensator
      8. 8.2.8 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Layout Procedure
    2. 10.2 Layout Examples
  11. 11Device and Documentation Support
    1. 11.1 Custom Design With WEBENCH® Tools
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.3.15 Soft-Start

The soft-start feature allows the controller to gradually reach the steady state operating point, thus reducing Start-up stresses and surges. The LM5141 regulates the FB pin to the SS pin voltage or the internal 1.2-V reference, whichever is lower. At the beginning of the soft-start sequence when SS = 0 V, the internal 20 µA soft-start current source gradually increases the voltage on an external soft-start capacitor connected to the SS pin, resulting in a gradual rise of the FB and output voltages. The controller is in the forced PWM (FPWM) mode when the DEMB pin is connected to VDDA. In this mode, the SS pin is clamped at 200 mV above the feedback voltage. This ensures that SS will be pulled low quickly when FB falls during brief over-current events to prevent overshoot of VOUT during recovery. SS can be pulled low with an external circuit to stop switching, but this is not recommended. Pulling SS low will result in COMP being pulled down internally as well. If the controller is operating in FPWM mode (DEMB = VDDA), LO will remain on and the low-side MOSFET will discharge the VOUT capacitor resulting in large negative inductor current. In contrast when the LM5141 pulls SS low internally due to a fault condition, the LO gate driver is disabled.