SLUSD66D September   2019  – February 2021 TPS92520-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  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  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  LED Current Regulation and Error Amplifier
      5. 7.3.5  Start-up Sequence
      6. 7.3.6  Analog Dimming and Forced Continuous Conduction Mode
      7. 7.3.7  External PWM Dimming and Input Undervoltage Lockout (UVLO)
      8. 7.3.8  Internal PWM Dimming
      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 ADC
        1. 7.3.12.1 Input Voltage Measurement: VINx
        2. 7.3.12.2 LED Voltage Measurement: CSNx
        3. 7.3.12.3 Bias Supply Measurement: V5D
        4. 7.3.12.4 External Limp-Home Input Measurement: LHI
        5. 7.3.12.5 Junction Temperature Measurement: TEMP
      13. 7.3.13 Faults and Diagnostics
      14. 7.3.14 Output Short Circuit Fault
      15. 7.3.15 Output Open Circuit Fault
    4. 7.4 Device Functional Modes
      1. 7.4.1 Power On Reset (POR)
      2. 7.4.2 Detect SPI Communication
      3. 7.4.3 Standalone Mode
      4. 7.4.4 Load Mode
      5. 7.4.5 Run Mode
      6. 7.4.6 Sleep Mode
      7. 7.4.7 Limp-Home Mode
    5. 7.5 Programming
      1. 7.5.1 Serial Interface
      2. 7.5.2 Command Frame
      3. 7.5.3 Response Frame
        1. 7.5.3.1 Read Response Frame Format
        2. 7.5.3.2 Write Response Frame Format
        3. 7.5.3.3 Write Error/POR Frame Format
      4. 7.5.4 SPI Error
      5. 7.5.5 SPI for Multiple Slave Devices in Parallel Configuration
      6. 7.5.6 SPI for Multiple Slave Devices in Daisy Chain Configuration
    6. 7.6 Register Maps
      1. 7.6.1 Configuration Registers
        1. 7.6.1.1 SYSCFG1 Register (address = 0x00) [reset = 0x10]
        2. 7.6.1.2 SYSCFG2 Register (address = 0x01) [reset = 0x00]
        3. 7.6.1.3 CMWTAP Register (address = 0x02) [reset = 0x08]
      2. 7.6.2 STATUS Registers
        1. 7.6.2.1 STATUS1 Register (address = 0x03)
        2. 7.6.2.2 STATUS2 Register (address = 0x04)
        3. 7.6.2.3 STATUS3 Register (address = 0x05)
      3. 7.6.3 Device Control Registers
        1. 7.6.3.1  Thermal Warning Limit (address = 0x06) [reset = 0x8A]
        2. 7.6.3.2  SLEEP Command (address = 0x07) [reset = 0x00]
        3. 7.6.3.3  CH1IADJL Control Register (address = 0x08) [reset = 0x00]
        4. 7.6.3.4  CH1IADJH Control Register (address = 0x09) [reset = 0x00]
        5. 7.6.3.5  CH2IADJL Control Register (address = 0x0A) [reset = 0x00]
        6. 7.6.3.6  CH2IADJH Control Register (address = 0x0B) [reset = 0x00]
        7. 7.6.3.7  PWMDIV Register (address = 0x0C) [reset = 0x04]
        8. 7.6.3.8  CH1PWML Register (address = 0x0D) [reset = 0x00]
        9. 7.6.3.9  CH1PWMH Register (address = 0x0E) [reset = 0x00]
        10. 7.6.3.10 CH2PWML Register (address = 0x0F) [reset = 0x00]
        11. 7.6.3.11 CH2PWMH Register (address = 0x10) [reset = 0x00]
        12. 7.6.3.12 CH1TON Register (address = 0x11) [reset = 0x07]
        13. 7.6.3.13 CH2TON Register (address = 0x12) [reset = 0x07]
      4. 7.6.4 ADC Measurements
        1. 7.6.4.1  CH1VIN Measurement (address = 0x13)
        2. 7.6.4.2  CH1VLED Measurement (address = 0x14)
        3. 7.6.4.3  CH1VLEDON Measurement (address = 0x15)
        4. 7.6.4.4  CH1VLEDOFF Measurement (address = 0x16)
        5. 7.6.4.5  CH2VIN Measurement (address = 0x17)
        6. 7.6.4.6  CH2VLED Measurement (address = 0x18)
        7. 7.6.4.7  CH2VLEDON Measurement (address = 0x19)
        8. 7.6.4.8  CH2VLEDOFF Measurement (address = 0x1A)
        9. 7.6.4.9  TEMPL Measurement (address = 0x1B)
        10. 7.6.4.10 TEMPH Measurement (address = 0x1C)
        11. 7.6.4.11 V5D Measurement (address = 0x1D)
      5. 7.6.5 Limp-Home Configuration and Command Registers
        1. 7.6.5.1  LHCFG1 Register (address = 0x1E) [reset =0x00]
        2. 7.6.5.2  LHCFG2 Register (address = 0x1F) [reset =0x00h]
        3. 7.6.5.3  LHIL Measurement (address = 0x20)
        4. 7.6.5.4  LHIH Measurement (address = 0x21)
        5. 7.6.5.5  LHIFILTL Register (address = 0x22)
        6. 7.6.5.6  LHIFILTH Register (address = 0x23)
        7. 7.6.5.7  LH1IADJL Register (address = 0x24) [reset = 0x00]
        8. 7.6.5.8  LH1IADJH Register (address = 0x25) [reset = 0x00]
        9. 7.6.5.9  LH2IADJL Register (address = 0x26) [reset = 0x00]
        10. 7.6.5.10 LH2IADJH Register (address = 0x27) [reset = 0x00]
        11. 7.6.5.11 LH1PWML Register (address = 0x28) [reset = 0x00]
        12. 7.6.5.12 LH1PWMH Register (address = 0x29) [reset = 0x00]
        13. 7.6.5.13 LH2PWML Register (address = 0x2A) [reset = 0x00]
        14. 7.6.5.14 LH2PWMH Register (address = 0x2B) [reset = 0x00]
        15. 7.6.5.15 LH1TON Register (address = 0x2C) [reset = 0x07]
        16. 7.6.5.16 LH2TON Register (address = 0x2D) [reset = 0x07]
      6. 7.6.6 RESET Register (address = 0x2E) (Write-Only)
  8. 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
        1. 8.2.1.1 Detailed Design Procedure
          1. 8.2.1.1.1 Calculating Duty Cycle
          2. 8.2.1.1.2 Calculating Minimum On-Time and Off-Time
          3. 8.2.1.1.3 Minimum Switching Frequency
          4. 8.2.1.1.4 LED Current Set Point
          5. 8.2.1.1.5 Inductor Selection
          6. 8.2.1.1.6 Output Capacitor Selection
          7. 8.2.1.1.7 Bootstrap Capacitor Selection
          8. 8.2.1.1.8 Compensation Capacitor Selection
          9. 8.2.1.1.9 External Channel Enable and PWM dimming
      2. 8.2.2 Application Curves
    3. 8.3 Initialization Setup
      1. 8.3.1 Initialize Device without Watchdog timer
      2. 8.3.2 Initialize Device with Watchdog Timer
      3. 8.3.3 Limp-Home Mode
  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 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

7.3.3 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 of 105 ns (typ) 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 4. GUID-53CD87CD-3B5B-45C9-849C-AEB92D498931-low.gif

The converter reaches the minimum off-time of 57 ns (typ) 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 CHxTOFFMIN bit is set to indicate operation at maximum duty cycle. The converter continues to switch unless disabled by resetting the CHxEN bit. Upon detection of a minimum off-time operation, the device disables the error amplifier and disconnects the COMP pin to maintain charge on the compensation network. This ensures fast response with minimum LED current overshoot as the converter recovers from dropout condition.

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 needs to exceed the minimum value, specified in Figure 6-5. At high (near 100%) or low (near 0%) duty cycles, the inductor current ripple may not be 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 may not 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.