JAJSCD8C August   2015  – May 2017 LP8861-Q1

PRODUCTION DATA.  

  1. 1 特長
  2. 2 アプリケーション
    1.     システム効率
  3. 3 概要
    1.     概略回路図
  4. 4 改訂履歴
  5. 5 デバイス比較表
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 7 Specifications
    1. 7.1  Absolute Maximum Ratings
    2. 7.2  ESD Ratings
    3. 7.3  Recommended Operating Conditions
    4. 7.4  Thermal Information
    5. 7.5  Electrical Characteristics
    6. 7.6  Internal LDO Electrical Characteristics
    7. 7.7  Protection Electrical Characteristics
    8. 7.8  Power Line FET Control Electrical Characteristics
    9. 7.9  Current Sinks Electrical Characteristics
    10. 7.10 PWM Brightness Control Electrical Characteristics
    11. 7.11 Boost/SEPIC Converter Characteristics
    12. 7.12 Logic Interface Characteristics
    13. 7.13 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Integrated Boost/SEPIC Converter
      2. 8.3.2 Internal LDO
      3. 8.3.3 LED Current Sinks
        1. 8.3.3.1 Current Sink Configuration
        2. 8.3.3.2 Current Setting
        3. 8.3.3.3 Brightness Control
      4. 8.3.4 Power-Line FET Control
      5. 8.3.5 LED Current Dimming With External Temperature Sensor
      6. 8.3.6 Protection and Fault Detection
        1. 8.3.6.1 Adaptive Boost Control and Functionality of LED Fault Comparators
        2. 8.3.6.2 Overview of the Fault/Protection Schemes
    4. 8.4 Device Functional Modes
      1. 8.4.1 Device States
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Typical Application for 4 LED Strings
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Inductor Selection
          2. 9.2.1.2.2 Output Capacitor Selection
          3. 9.2.1.2.3 Input Capacitor Selection
          4. 9.2.1.2.4 LDO Output Capacitor
          5. 9.2.1.2.5 Diode
          6. 9.2.1.2.6 Power Line Transistor
          7. 9.2.1.2.7 Input Current Sense Resistor
        3. 9.2.1.3 Application Curves
      2. 9.2.2 High Output Current Application
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
        3. 9.2.2.3 Application Curves
      3. 9.2.3 SEPIC Mode Application
        1. 9.2.3.1 Design Requirements
        2. 9.2.3.2 Detailed Design Procedure
          1. 9.2.3.2.1 Diode
          2. 9.2.3.2.2 Inductor
        3. 9.2.3.3 Application Curves
      4. 9.2.4 Application with Temperature Based LED Current De-rating
        1. 9.2.4.1 Design Requirements
        2. 9.2.4.2 Detailed Design Procedure
        3. 9.2.4.3 Application Curve
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12デバイスおよびドキュメントのサポート
    1. 12.1 デバイス・サポート
      1. 12.1.1 デベロッパー・ネットワークの製品に関する免責事項
    2. 12.2 ドキュメントのサポート
      1. 12.2.1 関連資料
    3. 12.3 ドキュメントの更新通知を受け取る方法
    4. 12.4 コミュニティ・リソース
    5. 12.5 商標
    6. 12.6 静電気放電に関する注意事項
    7. 12.7 Glossary
  13. 13メカニカル、パッケージ、および注文情報

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

8.3.6.1 Adaptive Boost Control and Functionality of LED Fault Comparators

Adaptive boost control function adjusts the boost output voltage to the minimum sufficient voltage for proper LED current sink operation. The output with highest VF LED string is detected and boost output voltage adjusted accordingly. Boost adaptive control voltage step size is defined by maximum boost voltage settings, VSTEP = (VMAX BOOST - VMIN BOOST) / 256. Periodic down pressure is applied to the target boost voltage to achieve better system efficiency.

Every LED current sink has 3 comparators for an adaptive boost control and fault detection. Comparator outputs are filtered, filtering time is 1 µs.

LP8861-Q1 compar_SNVSA50.gifFigure 14. Comparators for Adaptive Voltage Control and LED Fault Detection

Figure 15 illustrates different cases which cause boost voltage increase, decrease, or generate faults. In normal operation, voltage at all the OUT# pins is between LOW_COMP and MID_COMP levels and boost voltage stays constant. LOW_COMP level is the minimum for proper LED current sink operation, 1.1 × VSAT + 0.2 V (typical). MID_COMP level is 1.1 × VSAT + 1.2 V (typical) — that is, typical headroom window is 1 V.

When voltage at all the OUT# pins increases above MID_COMP level, boost voltage adapts downwards.

When voltage at any of the OUT# pins falls below LOW_COMP threshold, boost voltage adapts upwards. In the condition where boost voltage reaches the maximum and there are one or more outputs still below LOW_COMP level, an open LED fault is detected.

HIGH_COMP level, 6 V typical, is the threshold for shorted LED detection. When the voltage of one or more of the OUT# pins increases above HIGH_COMP level and at least one of the other outputs is within the normal headroom window, shorted LED fault is detected.

LP8861-Q1 algor_protect_SNVSA50.gifFigure 15. Boost Adaptation and LED Protection Algorithms