SLUSEG1A August   2021  – December 2021 TPS92519-Q1

PRODUCTION DATA  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  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. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Buck Converter Switching Operation
      2. 7.3.2  Switching Frequency and Adaptive On-Time Control
      3. 7.3.3  Minimum On-Time, Off-Time, and Inductor Ripple
      4. 7.3.4  Enable
      5. 7.3.5  LED Current Regulation and Error Amplifier
      6. 7.3.6  Start-up Sequence
      7. 7.3.7  Analog Dimming and Forced Continuous Conduction Mode
      8. 7.3.8  External PWM Dimming and Input Undervoltage Lockout (UVLO)
      9. 7.3.9  Shunt FET Dimming or Matrix Beam Application
      10. 7.3.10 Bias Supply
      11. 7.3.11 Bootstrap Supply
      12. 7.3.12 Faults and Diagnostics
      13. 7.3.13 Output Short Circuit Fault
      14. 7.3.14 Output Open Circuit Fault
      15. 7.3.15 Parallel Operation
    4. 7.4 Device Functional Modes
      1. 7.4.1 Power On Reset (POR)
      2. 7.4.2 Run Mode
      3. 7.4.3 Sleep Mode
  8. Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1  Duty Cycle Consideration
      2. 8.1.2  Switching Frequency Selection
      3. 8.1.3  LED Current Set Point
      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  Compensation Capacitor Selection
      9. 8.1.9  Input Undervoltage Protection
      10. 8.1.10 CSN Protection Diode
    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 Compensation Capacitor Selection
        9. 8.2.2.9 PWM Dimming and Input Voltage Protection
      3. 8.2.3 Application Curves
  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 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Support Resources
    4. 11.4 Trademarks
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

Minimum On-Time, Off-Time, and Inductor Ripple

Buck converter operation is impacted by minimum on-time, minimum off-time, and minimum peak-to-peak inductor ripple limitations. The converter reaches the minimum on-time when operating with high input voltage and low-output voltage. In this control scheme, the off-time continues to increase and the switching frequency reduces to regulate the inductor current and LED current to the desired value.

Equation 5. GUID-F37D796D-1566-488F-B279-21C937B25F93-low.gif

The converter reaches the minimum off-time when operating in dropout (low input voltage and high output voltage). As the on-time and off-time are fixed, the duty cycle is constant and the buck converter operates in open-loop mode. The inductor current and LED current are not in regulation. The converter continues to switch unless disabled by the IADJx input.

The behavior and response of valley comparator is dependent on sensed peak-to-peak voltage ripple, ΔV(CSP-CSN), and is a function of current sense resistor, RCS, and peak-to-peak inductor current ripple, ΔiL(PK-PK). To ensure periodic switching, the sensed peak-to-peak ripple must exceed the minimum value. At high (near 100%) or low (near 0%) duty cycles, the inductor current ripple is not sufficient to ensure periodic switching. Under such operating conditions, the converter transitions from periodic switching to a burst sequence, forcing multiple on-time and off-time cycles at a rate higher than the programmed frequency. Although the converter cannot operate in a periodic manner, the closed-loop control continues regulating the average LED current with a larger ripple value corresponding to higher peak-to-peak inductor ripple. TI recommends choosing an inductor, output capacitor, and switching frequency to ensure minimum sensed peak-to-peak ripple voltage under nominal operating condition is greater than 20 mV. The Application and Implementation section summarizes the detailed design procedure.