ZHCSQK6 May   2022 TPS92643-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  Internal Regulator
      2. 7.3.2  Buck Converter Switching Operation
      3. 7.3.3  Bootstrap Supply
      4. 7.3.4  Switching Frequency and Adaptive On-Time Control
      5. 7.3.5  Minimum On-Time, Off-Time, and Inductor Ripple
      6. 7.3.6  LED Current Regulation and Error Amplifier
      7. 7.3.7  Start-Up Sequence
      8. 7.3.8  Analog Dimming and Forced Continuous Conduction Mode
      9. 7.3.9  External PWM Dimming and Input Undervoltage Lockout (UVLO)
      10. 7.3.10 Analog Pulse Width Modulator Circuit
      11. 7.3.11 Output Short and Open-Circuit Faults
      12. 7.3.12 Overcurrent Protection
      13. 7.3.13 Thermal Shutdown
      14. 7.3.14 Fault Indicator and Diagnostics Summary
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1  Duty Cycle Considerations
      2. 8.1.2  Switching Frequency Selection
      3. 8.1.3  LED Current Programming
      4. 8.1.4  Inductor Selection
      5. 8.1.5  Output Capacitor Selection
      6. 8.1.6  Input Capacitor Selection
      7. 8.1.7  Bootstrap Capacitor Selection
      8. 8.1.8  Bootstrap Resistor Selection
      9. 8.1.9  Compensation Capacitor Selection
      10. 8.1.10 Input Dropout and Undervoltage Protection
      11. 8.1.11 APWM Input and Thermal Protection
      12. 8.1.12 Protection Diodes
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  Calculating Duty Cycle
        2. 8.2.2.2  Calculating Minimum On-Time and Off-Time
        3. 8.2.2.3  Minimum Switching Frequency
        4. 8.2.2.4  LED Current Set Point
        5. 8.2.2.5  Inductor Selection
        6. 8.2.2.6  Output Capacitor Selection
        7. 8.2.2.7  Bootstrap Capacitor Selection
        8. 8.2.2.8  Bootstrap Resistor Selection
        9. 8.2.2.9  Compensation Capacitor Selection
        10. 8.2.2.10 VIN Dropout Protection and PWM Dimming
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Compact Layout for EMI Reduction
        1. 10.1.1.1 Ground Plane
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 接收文档更新通知
    2. 11.2 支持资源
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 术语表
  12. 12Mechanical, Packaging, and Orderable Information

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7.3.7 Start-Up Sequence

The start-up circuit allows the COMP pin voltage to gradually increase, thus reducing the LED current overshoot and current surges. The switching operation is initiated after the COMP pin voltage exceeds 2.45 V. A 440-mV hysteresis window allows the device to operate when COMP voltage is within the expected operating range of 2.2 V to 2.7 V. Switching is disabled on detection of low COMP voltage to avoid excessive negative inductor current.

The duration of soft start, tss, depends on the size of the compensation capacitor and the error amplifier source current, ICOMP(SRC).

Equation 6. t S S = 2.45 × C C O M P I C O M P S R C

The source current, ICOMP(SRC) is a function of the transconductance, gM, of the error amplifier and error generated between the reference and the current sensed voltage.

Equation 7. I C O M P S R C = g M × ( V I A D J 14 - V ( C S P - C S N ) )

With no current flowing through the LEDs, the soft start duration depends on the choice of compensation capacitor, CCOMP, and the reference voltage, VIADJ.

Figure 7-4 Soft-Start Sequence

The open drain fault indicator, FLT, is set low when the COMP voltage deviates from the nominal range and exceeds VCOMP(OV) threshold. This setting indicates a fault condition where the converter is operating in open-loop and the LED current is out of regulation. The device can be disabled by setting IADJ input below 100 mV or controlling the UDIM input.