SNVS699I February   2011  – May 2026 LM5045

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1  High-Voltage Start-Up Regulator
      2. 6.3.2  Line Undervoltage Detector
      3. 6.3.3  Overvoltage Protection
      4. 6.3.4  Reference
      5. 6.3.5  Oscillator, Sync Input
      6. 6.3.6  Cycle-by-Cycle Current Limit
      7. 6.3.7  Hiccup Mode
      8. 6.3.8  PWM Comparator
      9. 6.3.9  Ramp Pin
      10. 6.3.10 Slope Pin
      11. 6.3.11 Soft-Start
      12. 6.3.12 Gate Driver Outputs
      13. 6.3.13 Synchronous Rectifier Control Outputs (SR1 and SR2)
      14. 6.3.14 Soft-Start of the Synchronous Rectifiers
      15. 6.3.15 Prebias Startup
      16. 6.3.16 Soft-Stop
      17. 6.3.17 Soft-Stop Off
      18. 6.3.18 Thermal Protection
    4. 6.4 Device Functional Modes
      1. 6.4.1 Control Method Selection
      2. 6.4.2 Voltage Mode Control Using the LM5045
      3. 6.4.3 Current Mode Control Using the LM5045
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 VIN and VCC
        2. 7.2.2.2 For Applications With > 100 VIN
        3. 7.2.2.3 UVLO and OVP Voltage Divider Selection
        4. 7.2.2.4 Current Sense
        5. 7.2.2.5 Hiccup Mode Current Limit Restart
        6. 7.2.2.6 Augmenting the Gate Drive Strength
      3. 7.2.3 Application Curve
  9. 8 Power Supply Recommendations
  10. 9 Layout
    1. 9.1 Layout Guidelines
    2. 9.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Receiving Notification of Documentation Updates
    2. 10.2 Support Resources
    3. 10.3 Trademarks
    4. 10.4 Electrostatic Discharge Caution
    5. 10.5 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information

Package Options

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

6.3.6 Cycle-by-Cycle Current Limit

The CS pin is to be driven by a signal representative of the primary current of the transformer. If the voltage on the CS pin exceeds 0.75 V, the current sense comparator immediately terminates the PWM cycle. A small RC filter connected to the CS pin and located near the controller is recommended to suppress noise. An internal 18-Ω MOSFET discharges the external current sense filter capacitor at the conclusion of every cycle. The discharge MOSFET remains on for an additional 40 ns after the start of a new PWM cycle to blank leading edge spikes. The current sense comparator is very fast and may respond to short duration noise pulses. Layout is critical for the current sense filter and the sense resistor. The capacitor associated with CS filter must be placed very close to the device and connected directly to the CS and AGND pins. If a current sense transformer is used, both the leads of the transformer secondary should be routed to the filter network, which should be located close to the IC. When designing with a current sense resistor, all of the noise sensitive low power ground connections should be connected together near the AGND pin, and a single connection should be made to the power ground (sense resistor ground point).