ZHCSPC5 October   2022 LM51231-Q1

PRODUCTION DATA  

  1. 1 特性
  2. 2 应用
  3. 3 说明
  4. 4 Revision History
  5. 5 Pin Configuration and 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 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  Device Enable/Disable (EN, VH Pin)
      2. 7.3.2  High Voltage VCC Regulator (BIAS, VCC Pin)
      3. 7.3.3  Light Load Switching Mode Selection (MODE Pin)
      4. 7.3.4  VOUT Range Selection (RANGE Pin)
      5. 7.3.5  Line Undervoltage Lockout (UVLO Pin)
      6. 7.3.6  Fast Restart using VCC HOLD (VH Pin)
      7. 7.3.7  Adjustable Output Regulation Target (VOUT, TRK, VREF Pin)
      8. 7.3.8  Overvoltage Protection (VOUT Pin)
      9. 7.3.9  Power Good Indicator (PGOOD Pin)
      10. 7.3.10 Dynamically Programmable Switching Frequency (RT)
      11. 7.3.11 External Clock Synchronization (SYNC Pin)
      12. 7.3.12 Programmable Spread Spectrum (DITHER Pin)
      13. 7.3.13 Programmable Soft-start (SS Pin)
      14. 7.3.14 Wide Bandwidth Transconductance Error Amplifier and PWM (TRK, COMP Pin)
      15. 7.3.15 Current Sensing and Slope Compensation (CSP, CSN Pin)
      16. 7.3.16 Constant Peak Current Limit (CSP, CSN Pin)
      17. 7.3.17 Maximum Duty Cycle and Minimum Controllable On-time Limits
      18. 7.3.18 MOSFET Drivers, Integrated Boot Diode, and Hiccup Mode Fault Protection (LO, HO, HB Pin)
      19. 7.3.19 Thermal Shutdown Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 Device Status
        1. 7.4.1.1 Shutdown Mode
        2. 7.4.1.2 Configuration Mode
        3. 7.4.1.3 Active Mode
        4. 7.4.1.4 Bypass Mode
          1. 7.4.1.4.1 Bypass DE mode
          2. 7.4.1.4.2 Bypass FPWM
      2. 7.4.2 Light Load Switching Mode
        1. 7.4.2.1 Forced PWM (FPWM) Mode
        2. 7.4.2.2 Diode Emulation (DE) Mode
        3. 7.4.2.3 Forced Diode Emulation Operation in FPWM Mode
  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
      3. 8.2.3 Application Ideas
      4. 8.2.4 Application Curves
    3. 8.3 System Example
    4. 8.4 Power Supply Recommendations
    5. 8.5 Layout
      1. 8.5.1 Layout Guidelines
      2. 8.5.2 Layout Example
  9. 9 Device and Documentation Support
    1. 9.1 接收文档更新通知
    2. 9.2 支持资源
    3. 9.3 Trademarks
    4. 9.4 Electrostatic Discharge Caution
    5. 9.5 术语表
  10. 10Mechanical, Packaging, and Orderable Information

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7.3.12 Programmable Spread Spectrum (DITHER Pin)

The device provides an optional programmable spread spectrum (clock dithering) function that is activated by connecting a capacitor between DITHER and AGND. A triangular waveform centered at 1.0 V is generated across the dither capacitor. This triangular waveform modulates the oscillator frequency by –6% to +5% of the frequency set by the RT resistor. The dither capacitance value sets the rate of the low frequency modulation.

GUID-60727FB4-EA85-4BEA-AE20-8879326ACB80-low.gifFigure 7-10 Switching Frequency Dithering

For the dithering circuit to effectively reduce peak EMI, the modulation frequency must be much less than the RT switching frequency. The dither capacitance which is required for a given modulation frequency (fMOD), can be calculated from Equation 9. Setting the fMOD to 9 kHz or 10 kHz is a good starting point.

Equation 9. CDITHER=20μAfMOD×0.29

Connecting DITHER to AGND deactivates clock dithering, and the internal oscillator operates at a fixed frequency set by the RT resistor. Clock dithering is also disabled when an external synchronization pulse is applied.

GUID-60C34985-7F5F-4A12-B176-CBC0CEDF0D68-low.gifFigure 7-11 Dynamic Dither On/Off Example