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

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7.2.2.4 Current Sense

The CS pin receives an input signal representative of its transformer’s primary current, either from a current sense transformer or from a resistor located at the junction of source pin of the primary switches, as shown in Figure 7-9 and Figure 7-10, respectively. In both the cases, the filter components RF and CF should be located as close to the IC as possible, and the ground connection from the current sense transformer, or RSENSE should be a dedicated trace to the appropriate GND pin. Please refer to the Section 9 section for more layout tips.

The current sense components must provide a signal > 710 mV at the CS pin during an over-load event. Once the voltage on the CS pin crosses the current limit threshold, the current sense comparator terminates the PWM pulse and starts to charge the RES pin. Depending on the configuration of the RES pin, the LM5045 will eventually initiate a hiccup mode restart or be in continuous current limit.

LM5045 Transformer Current SenseFigure 7-9 Transformer Current Sense
LM5045 Resistor Current Sense Figure 7-10 Resistor Current Sense