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

8.3.5 LED Current Dimming With External Temperature Sensor

The LP8861-Q1 has an optional feature to decrease automatically LED current when LED overheating is detected with an external NTC sensor. An example of the behavior is shown in Figure 11. When the NTC temperature reaches T1, the LP8861-Q1 starts to decrease the LED current. When the LED current has reduced to 17.5% of the nominal value, current turns off until temperature returns to the operation range. When TSET pin is grounded this feature is disabled. Temperature T1 and de-rate slope are defined by external resistors as explained below.

LP8861-Q1 temper_dimm_SNVSA50.gifFigure 11. Temperature-Based LED Current Dimming Functionality
LP8861-Q1 temper_implem_SNVSA50.gifFigure 12. Temperature-Based LED Current Dimming Implementation

When the TSET pin is grounded LED current is set by RISET resistor:

Equation 4. LP8861-Q1 form_current_SNVSA50.gif

When external NTC is connected, the TSENSE pin current decreases LED output current. The following steps describe how to calculate LED output current.

Parallel resistance of the NTC sensor RT and resistor R4 is calculated by formula:

Equation 5. LP8861-Q1 form_temper02_SNVSA50.gif

TSET voltage can be calculated with Equation 6:

Equation 6. LP8861-Q1 form_temper03_SNVSA50.gif

TSENSE pin current is calculated by Equation 7:

Equation 7. LP8861-Q1 form_temper04_SNVSA50.gif

ISET pin current defined by RISET is:

Equation 8. LP8861-Q1 form_temper01_SNVSA50.gif

For Equation 9, ITSENSE current must be limited between 0 and ISET_SCALED. If ITSENSE > ISET_SCALED then set ITSENSE = ISET_SCALED. If ITSENSE < 0 then set ITSENSE = 0.

LED driver output current is:

Equation 9. ILED = (ISET_SCALED – ITSENSE ) x 2 000

When current is lower than 17.5% of the nominal value, the current is set to 0 (so called cut-off point).

An Excel® calculator is available for calculating the component values for a specific NTC and target thermal profile (contact your local TI representative). Figure 13 shows an example thermal profile implementation.

LP8861-Q1 C006_SNVSA50.png
NTC – 10 kΩ at 25ºC RISET = 24 kΩ R2 = 10 kΩ R4 = 100 kΩ
VDD = 4.3 V R1 = 10 kΩ R3 = 2 kΩ R5 = 7.5 kΩ
Figure 13. Calculation Example