SNVSBT4A August   2023  – November 2023 LM5185-Q1

PRODUCTION DATA  

  1.   1
  2. Features
  3. Applications
  4. Description
  5. Description (continued)
  6. Pin Configuration and Functions
  7. 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 Typical Characteristics
  8. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Power MOSFET Gate Driver
      2. 7.3.2  PSR Flyback Modes of Operation
      3. 7.3.3  High Voltage VCC Regulator
      4. 7.3.4  Setting the Output Voltage
        1. 7.3.4.1 Diode Thermal Compensation
      5. 7.3.5  Control Loop Error Amplifier
      6. 7.3.6  Precision Enable
      7. 7.3.7  Configurable Soft Start
      8. 7.3.8  Minimum On-Time and Off-Time
      9. 7.3.9  Current Sensing and Overcurrent Protection
      10. 7.3.10 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Standby Mode
      3. 7.4.3 Active Mode
  9. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Design 1: Wide VIN, Low IQ PSR Flyback Converter Rated at 16.4 V, 1 A
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1  Custom Design With WEBENCH® Tools
          2. 8.2.1.2.2  Custom Design With Excel Quickstart Tool
          3. 8.2.1.2.3  Flyback Transformer T1 and Current-Sense Resistor (RCS)
          4. 8.2.1.2.4  Flyback Diode – DFLY
          5. 8.2.1.2.5  Leakage Inductance Clamp Circuit – DF, DCLAMP
          6. 8.2.1.2.6  Feedback Resistor – RFB
          7. 8.2.1.2.7  Thermal Compensation Resistor – RTC
          8. 8.2.1.2.8  UVLO Resistors – RUV1, RUV2
          9. 8.2.1.2.9  Soft-Start Capacitor – CSS
          10. 8.2.1.2.10 Compensation Components
        3. 8.2.1.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Examples
  10. Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Development Support
        1. 9.1.1.1 Custom Design With WEBENCH® Tools
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

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

Choose compensation components for a stable control loop using the procedure outlined as follows.

First, calculate the power stage transfer function with Equation 26. Lmag is the magnetizing inductance of the transformer. Cout is the output capacitance. Rload is the load resistance.

Equation 26. Gpws=AM×ACS×(1-sωzRHP)(1+sωzESR)1+sωp

where

Equation 27. AM=Rload×Nps×(1-D)2×(1+D)
Equation 28. ACS=110×RCS
Equation 29. ωzRHP=1-D2DRload×Nps2Lmag
Equation 30. ωzESR=1Cout×RESR
Equation 31. ωp=1+DCout×Rload

Next, use Equation 32 to calculate the power stage gain at the cross-over frequency Fco which is selected to be 1 kHz for this design.

Equation 32. GainFco=20×log(Gpw(2j×π×Fco))

Select RCOMP to satisfy the desired cross-over frequency.

Equation 33. R C O M P = 10 - G a i n F c o 20 g m   R F B 100   μA V r e f

Select CCOMP to set the compensator zero at 2 times of the load pole.

Equation 34. CCOMP=12×ωp×RCOMP

Select CHF to set the compensator pole at 50 to 200 times the compensator zero.

Equation 35. CHF=CCOMP150