SNVS857 February   2014 LP8555

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Simplified Schematic
  5. 5 Revision History
  6. 6 Terminal Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 Handling Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 I2C Serial Bus Timing Parameters (FSET/SDA, ISET/SCL)
    7. 7.7 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Features Description
      1. 8.3.1 Boost Converter Overview
        1. 8.3.1.1 Operation
        2. 8.3.1.2 Protection
        3. 8.3.1.3 Setting Boost Switching Frequency
        4. 8.3.1.4 Adaptive Boost Output Voltage Control
        5. 8.3.1.5 EMI Reduction
      2. 8.3.2 Brightness Control
        1. 8.3.2.1 PWM Input Duty Measurement
        2. 8.3.2.2 BRTMODE = 00
        3. 8.3.2.3 BRTMODE = 01
        4. 8.3.2.4 BRTMODE = 10
        5. 8.3.2.5 BRTMODE = 11
        6. 8.3.2.6 Hybrid PWM and Current Dimming Control
        7. 8.3.2.7 Setting PWM Dimming Frequency
        8. 8.3.2.8 Setting Full-Scale LED Current
        9. 8.3.2.9 Phase-Shift PWM Scheme
      3. 8.3.3 LED Brightness Slopes, Normal and Advanced
      4. 8.3.4 Start-up and Shutdown Sequences
        1. 8.3.4.1 Start-up With PWM Input Brightness Control Mode (BRTMODE = 00b)
        2. 8.3.4.2 Shutdown With PWM Input Brightness Control Mode (BRTMODE = 00b)
        3. 8.3.4.3 Start-up With I2C Brightness Control Mode (BRTMODE = 01b)
        4. 8.3.4.4 Shutdown With I2C Brightness Control Mode (BRTMODE = 01b)
        5. 8.3.4.5 Start-up with I2C + PWM Input Brightness Control Mode (BRTMODE = 10 or 11b)
        6. 8.3.4.6 Shutdown with I2C + PWM Input Brightness Control Mode (BRTMODE = 10 or 11b)
      5. 8.3.5 LED String Count Auto Detection
      6. 8.3.6 Fault Detection
        1. 8.3.6.1 LED Short Detection
        2. 8.3.6.2 LED Open Detection
        3. 8.3.6.3 Undervoltage Detection
        4. 8.3.6.4 Thermal Shutdown
        5. 8.3.6.5 Boost Overcurrent Protection
        6. 8.3.6.6 Boost Overvoltage Protection
        7. 8.3.6.7 Boost Undervoltage Protection
      7. 8.3.7 I2C-Compatible Serial Bus Interface
        1. 8.3.7.1 Interface Bus Overview
        2. 8.3.7.2 Data Transactions
        3. 8.3.7.3 Acknowledge Cycle
        4. 8.3.7.4 “Acknowledge After Every Byte” Rule
        5. 8.3.7.5 Addressing Transfer Formats
        6. 8.3.7.6 Control Register Write Cycle
        7. 8.3.7.7 Control Register Read Cycle
    4. 8.4 Device Functional Modes
      1. 8.4.1 Operation Without I2C Control
      2. 8.4.2 Operation With I2C Control
      3. 8.4.3 Shutdown Mode
      4. 8.4.4 Standby Mode
      5. 8.4.5 Active Mode
    5. 8.5 Register Maps
      1. 8.5.1  COMMAND
      2. 8.5.2  STATUS/MASK
      3. 8.5.3  BRTLO
      4. 8.5.4  BTHI
      5. 8.5.5  CONFIG
      6. 8.5.6  CURRENT
      7. 8.5.7  PGEN
      8. 8.5.8  BOOST
      9. 8.5.9  LEDEN
      10. 8.5.10 STEP
      11. 8.5.11 Brightness Transitions, Typical Times
      12. 8.5.12 VOLTAGE_0
      13. 8.5.13 LEDEN1
      14. 8.5.14 VOLTAGE1
      15. 8.5.15 OPTION
      16. 8.5.16 EXTRA
      17. 8.5.17 ID
      18. 8.5.18 REVISION
      19. 8.5.19 CONF0
      20. 8.5.20 CONF1
      21. 8.5.21 VHR0
      22. 8.5.22 VHR1
      23. 8.5.23 JUMP
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Application for Default LP8555YFQR EPROM Configuration
        1. 9.2.1.1 Schematic
        2. 9.2.1.2 LP8555YFQR EPROM Configuration
        3. 9.2.1.3 Design Requirements
        4. 9.2.1.4 Detailed Design Procedure
          1. 9.2.1.4.1 Inductor
          2. 9.2.1.4.2 Output Capacitor
          3. 9.2.1.4.3 LDO Capacitor
          4. 9.2.1.4.4 VDD Capacitor
          5. 9.2.1.4.5 Boost Input Capacitor
          6. 9.2.1.4.6 Diode
        5. 9.2.1.5 Application Performance Plots
      2. 9.2.2 Application Example With Different LED Configuration for Each Bank
        1. 9.2.2.1 Schematic
      3. 9.2.3 Application Example With 12 LED Strings and PWM Input Brightness Control
        1. 9.2.3.1 Schematic
      4. 9.2.4 Application With 12 LED Strings, I2C Brightness Control
        1. 9.2.4.1 Schematic
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12 Device and Documentation Support
    1. 12.1 Trademarks
    2. 12.2 Electrostatic Discharge Caution
    3. 12.3 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

1 Features

  • Dual High-Efficiency DC/DC Boost Converters
  • 2.7-V to 20-V VDD Range
  • 12 50-mA High-Precision LED Current Sinks With 12-Bit Brightness Control
  • Adaptive LED Current Sink Headroom Controls for Maximum System Efficiency
  • LED String Count Auto-Detection
  • Phase-Shifted PWM Mode for Reduced Audible Noise
  • PWM Input Duty-Cycle and/or I2C-Register Brightness Control
  • Hybrid PWM and Current Dimming for Higher LED Drive Optical Efficiency
  • Flexible CABC Support
  • EPROM, I2C-Register, or External Resistors for Configuration
  • Improved Boost EMI Performance with Slew-Rate Control, Spread Spectrum, and Phase-Shifted Switching
  • Extensive Fault Detection Schemes

2 Applications

  • Tablet LCD Display LED Backlight

3 Description

The LP8555 is a high efficiency LED driver with integrated dual DC-DC boost converters. It has 12 high-precision current sinks that can be controlled by a PWM input signal, an I2C master, or both.

Dual-boost configuration of LP8555 shares the load to two inductors and allows thinner overall solution size and better efficiency compared to single-boost solutions. 12 LED strings allows driving high number of LEDs with optimal efficiency since boost conversion ratio can be kept low.

The boost converter has adaptive output voltage control based on the LED current sink headroom voltages. This feature minimizes the power consumption by adjusting the voltage to lowest sufficient level in all conditions.

The LED string auto-detect function enables use of the same device in systems with 2 to 12 LED strings for the maximum design flexibility. Proprietary Hybrid PWM and Current dimming mode enables additional system power savings. Phase-shift PWM allows reduced audible noise and smaller boost output capacitors. Flexible CABC support combines brightness level selections based on the PWM input and I2C commands.

Device Information

ORDER NUMBER PACKAGE BODY SIZE
LP8555YFQR DSBGA (36) 2,478mm x 2,478mm

4 Simplified Schematic

typ_app_I2C_snvs857.gif

LED Drive Efficiency

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