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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発注情報

6.3.6 LED Current Regulation and Error Amplifier

The reference voltage, VIADJ, set by the VIADJ and is internally scaled by a gain factor of 1/14 through a resistor network. An internal rail-to-rail error amplifier generates an error signal proportional to the difference between the scaled reference voltage (VIADJ / 14) and the inductor current measured by the differential voltage drop between CSP and CSN, V(CSP-CSN). This error drives the COMP pin voltage, VCOMP, and directly controls the valley threshold of the inductor current. Zero average DC error and closed-loop regulation is achieved by implementing an integral compensation network consisting of a capacitor connected from the output of the error amplifier to GND. As a good starting point, TI recommends a capacitor value between 1 nF and 10 nF between the COMP pin and GND. The choice of compensation network must ensure a minimum of 60° of phase margin and 10 dB of gain margin.

GUID-20220512-SS0I-29RB-BM4V-GHDQ4NQVGNN2-low.svg Figure 6-3 Closed-Loop LED Current Regulation

LED current is dependent on the current sense resistor, RCS. Use Equation 17 to calculate the LED current.

TI recommends a Schottky diode connected from PGND to SW placed close to the device for LED current greater than 4-A and operating frequency is above 1-MHz. The diode reduces the impact of high frequency noise on PGND from impacting the valley detection circuit. The diode only conducts for a brief period of time and hence the impact on efficiency is negligible.

GUID-20231029-SS0I-VW4Q-JXXX-56NDFHLJZXHT-low.svg Figure 6-4 Switch node Schottky diode connection

LED current accuracy is a function of the tolerance of the external sense resistor, RCS, and the variation in the sense threshold, V(CSP-CSN), caused by internal mismatch and temperature dependency of the analog components. The TPS92642-Q1 incorporates low offset rail-to-rail amplifiers, and is capable of achieving LED current accuracy of ±4% over common-mode range and a junction temperature range of –40°C to 150°C.