SLUSE50 November   2023 TPS92642-Q1

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  Internal Regulator
      2. 6.3.2  Buck Converter Switching Operation
      3. 6.3.3  Bootstrap Supply
      4. 6.3.4  Switching Frequency and Adaptive On-Time Control
      5. 6.3.5  Minimum On-Time, Off-Time, and Inductor Ripple
      6. 6.3.6  LED Current Regulation and Error Amplifier
      7. 6.3.7  Start-Up Sequence
      8. 6.3.8  Analog Dimming and Forced Continuous Conduction Mode
      9. 6.3.9  External PWM Dimming and Input Undervoltage Lockout (UVLO)
      10. 6.3.10 Pulse Duty Cycle Limit Circuit
      11. 6.3.11 Output Short and Open-Circuit Faults
      12. 6.3.12 Overcurrent Protection
      13. 6.3.13 Thermal Shutdown
      14. 6.3.14 Fault Indicator and Diagnostics Summary
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1  Duty Cycle Considerations
      2. 7.1.2  Switching Frequency Selection
      3. 7.1.3  LED Current Programming
      4. 7.1.4  Inductor Selection
      5. 7.1.5  Output Capacitor Selection
      6. 7.1.6  Input Capacitor Selection
      7. 7.1.7  Bootstrap Capacitor Selection
      8. 7.1.8  Compensation Capacitor Selection
      9. 7.1.9  Input Dropout and Undervoltage Protection
      10. 7.1.10 Pulse Duty Cycle Limit Circuit
      11. 7.1.11 Protection Diodes
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 Calculating Duty Cycle
        2. 7.2.2.2 Calculating Minimum On-Time and Off-Time
        3. 7.2.2.3 Minimum Switching Frequency
        4. 7.2.2.4 LED Current Set Point
        5. 7.2.2.5 Inductor Selection
        6. 7.2.2.6 Output Capacitor Selection
        7. 7.2.2.7 Bootstrap Capacitor Selection
        8. 7.2.2.8 Compensation Capacitor Selection
        9. 7.2.2.9 VIN Dropout Protection and PWM Dimming
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
        1. 7.4.1.1 Compact Layout for EMI Reduction
          1. 7.4.1.1.1 Ground Plane
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Receiving Notification of Documentation Updates
    2. 8.2 Support Resources
    3. 8.3 Trademarks
    4. 8.4 Electrostatic Discharge Caution
    5. 8.5 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

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6.3.4 Switching Frequency and Adaptive On-Time Control

The TPS92642-Q1 uses an adaptive on-time control scheme and does not have a dedicated on-board oscillator. The one-shot timer is programmed by the RON resistor. The on-time is calculated internally using Equation 1 and is inversely proportional to the measured input voltage, VIN, and directly proportional to the measured CSP voltage, VCSP.

Equation 1. t O N = 10 × 10 - 12 × R O N × V C S P V I N

Given the duty ratio of the buck converter is VCSP/VIN, the switching period, TSW, remains nearly constant over different operating points. Use Equation 2 to calculate the switching period.

Equation 2. T S W = t O N × V I N V C S P = 10 × 10 - 12 × R O N

The switching frequency is calculated internally using Equation 3.

Equation 3. f S W = 1 10 × 10 - 12 × R O N

The minimum or maximum duty cycle is limited to finite minimum on-time, TON(MIN) and minimum off-time, TOFF(MIN), respectively. As on-time is constant, the frequency is also a dependent on the efficiency of the device, ηREG, excluding inductor and sense resistor losses.

Equation 21. f S W = 1 10 × 10 - 12 × R O N × η R E G

TI recommends a switching frequency setting between 100 kHz and 2.2 MHz.
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