SNVSBK8B october   2020  – august 2023 LM5157-Q1 , LM51571-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Revision History
  6. 5 Description (continued)
  7. 6 Device Comparison Table
  8. 7 Pin Configuration and Functions
  9. 8 Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 ESD Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Typical Characteristics
  10. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1  Line Undervoltage Lockout (UVLO/SYNC/EN Pin)
      2. 9.3.2  High Voltage VCC Regulator (BIAS, VCC Pin)
      3. 9.3.3  Soft Start (SS Pin)
      4. 9.3.4  Switching Frequency (RT Pin)
      5. 9.3.5  Dual Random Spread Spectrum – DRSS (MODE Pin)
      6. 9.3.6  Clock Synchronization (UVLO/SYNC/EN Pin)
      7. 9.3.7  Current Sense and Slope Compensation
      8. 9.3.8  Current Limit and Minimum On Time
      9. 9.3.9  Feedback and Error Amplifier (FB, COMP Pin)
      10. 9.3.10 Power-Good Indicator (PGOOD Pin)
      11. 9.3.11 Hiccup Mode Overload Protection (MODE Pin)
      12. 9.3.12 Maximum Duty Cycle Limit and Minimum Input Supply Voltage
      13. 9.3.13 Internal MOSFET (SW Pin)
      14. 9.3.14 Overvoltage Protection (OVP)
      15. 9.3.15 Thermal Shutdown (TSD)
    4. 9.4 Device Functional Modes
      1. 9.4.1 Shutdown Mode
      2. 9.4.2 Standby Mode
      3. 9.4.3 Run Mode
        1. 9.4.3.1 Spread Spectrum Enabled
        2. 9.4.3.2 Hiccup Mode Protection Enabled
  11. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Custom Design With WEBENCH® Tools
        2. 10.2.2.2 Recommended Components
        3. 10.2.2.3 Inductor Selection (LM)
        4. 10.2.2.4 Output Capacitor (COUT)
        5. 10.2.2.5 Input Capacitor
        6. 10.2.2.6 Diode Selection
      3. 10.2.3 Application Curve
    3. 10.3 System Examples
  12. 11Power Supply Recommendations
  13. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Examples
  14. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Third-Party Products Disclaimer
      2. 13.1.2 Development Support
        1. 13.1.2.1 Custom Design With WEBENCH® Tools
      3. 13.1.3 Export Control Notice
    2. 13.2 Documentation Support
      1. 13.2.1 Related Documentation
    3. 13.3 Receiving Notification of Documentation Updates
    4. 13.4 Support Resources
    5. 13.5 Trademarks
    6. 13.6 Electrostatic Discharge Caution
    7. 13.7 Glossary
  15. 14Mechanical, Packaging, and Orderable Information

Package Options

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

9.3.9 Feedback and Error Amplifier (FB, COMP Pin)

The feedback resistor divider is connected to an internal transconductance error amplifier that features high output resistance (RO = 10 MΩ) and wide bandwidth (BW = 7 MHz). The internal transconductance error amplifier sources current, which is proportional to the difference between the FB pin and the SS pin voltage or the internal reference, whichever is lower. The internal transconductance error amplifier provides symmetrical sourcing and sinking capability during normal operation and reduces its sinking capability when the FB is greater than OVP threshold.

To set the output regulation target, select the feedback resistor values as shown in Equation 9.

Equation 9. GUID-BBC1CDDB-B5D9-49E2-8062-6D7B0F0FD653-low.gif

The output of the error amplifier is connected to the COMP pin, allowing the use of a Type 2 loop compensation network. RCOMP, CCOMP, and optional CHF loop compensation components configure the error amplifier gain and phase characteristics to achieve a stable loop response. The absolute maximum voltage rating of the FB pin is 4.0 V. If necessary, especially during automotive load dump transient, the feedback resistor divider input can be clamped by using an external zener diode.

The COMP pin features internal clamps. The maximum COMP clamp limits the maximum COMP pin voltage below its absolute maximum rating even in shutdown. The minimum COMP clamp limits the minimum COMP pin voltage to start switching as soon as possible during no load to heavy load transition. The minimum COMP clamp is disabled when FB is connected to ground in flyback topology.