SNVSB83B June   2019  – January 2020 LP8867-Q1 , LP8869-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Simplified Schematic
    2.     LED Backlight Efficiency
  4. 4 Revision History
  5. 5 Device Comparison Table
  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  Current Sinks Electrical Characteristics
    9. 7.9  PWM Brightness Control Electrical Characteristics
    10. 7.10 Boost and SEPIC Converter Characteristics
    11. 7.11 Logic Interface Characteristics
    12. 7.12 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 DC-DC Converter
        1. 8.3.1.1 DC-DC Converter Parameter Configuration
          1. 8.3.1.1.1 Switching Frequency
          2. 8.3.1.1.2 Spread Spectrum and External SYNC
          3. 8.3.1.1.3 Recommended Component Value and Internal Parameters
          4. 8.3.1.1.4 DC-DC Converter Switching Current Limit
          5. 8.3.1.1.5 DC-DC Converter Light Load Mode
        2. 8.3.1.2 Adaptive Voltage Control
          1. 8.3.1.2.1 Using Two-Divider
          2. 8.3.1.2.2 Using T-Divider
          3. 8.3.1.2.3 Feedback Capacitor
      2. 8.3.2 Internal LDO
      3. 8.3.3 LED Current Sinks
        1. 8.3.3.1 LED Output Configuration
        2. 8.3.3.2 LED 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 Fault Detections and Protection
        1. 8.3.6.1 Supply Fault and Protection
          1. 8.3.6.1.1 VIN Undervoltage Fault (VIN_UVLO)
          2. 8.3.6.1.2 VIN Overvoltage Fault (VIN_OVP)
          3. 8.3.6.1.3 VIN Overcurrent Fault (VIN_OCP)
        2. 8.3.6.2 Boost Fault and Protection
          1. 8.3.6.2.1 Boost Overvoltage Fault (BST_OVP)
          2. 8.3.6.2.2 SW Overvoltage Fault (SW_OVP)
        3. 8.3.6.3 LED Fault and Protection (LED_OPEN and LED_SHORT)
        4. 8.3.6.4 Thermal Fault and Protection (TSD)
        5. 8.3.6.5 Overview of the Fault and Protection Schemes
    4. 8.4 Device Functional Modes
      1. 8.4.1 STANDBY State
      2. 8.4.2 SOFT START State
      3. 8.4.3 BOOST START State
      4. 8.4.4 NORMAL State
      5. 8.4.5 FAULT RECOVERY State
      6. 8.4.6 State Diagram and Timing Diagram for Start-up and Shutdown
  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
      2. 9.2.2 Design Requirements
      3. 9.2.3 Detailed Design Procedure
        1. 9.2.3.1 Inductor Selection
        2. 9.2.3.2 Output Capacitor Selection
        3. 9.2.3.3 Input Capacitor Selection
        4. 9.2.3.4 LDO Output Capacitor
        5. 9.2.3.5 Diode
      4. 9.2.4 Application Curves
      5. 9.2.5 SEPIC Mode Application
        1. 9.2.5.1 Design Requirements
        2. 9.2.5.2 Detailed Design Procedure
          1. 9.2.5.2.1 Inductor
          2. 9.2.5.2.2 Diode
          3. 9.2.5.2.3 Capacitor C1
        3. 9.2.5.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Development Support
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Community Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.3.5 LED Current Dimming With External Temperature Sensor

The LP886x-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 15. When the NTC temperature reaches T1, the LP886x-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.

LP8867-Q1 LP8869-Q1 cht-05-NTC-curve.gifFigure 15. Temperature-Based LED Current Dimming Functionality
LP8867-Q1 LP8869-Q1 cht-06-NTC-imple.gifFigure 16. Temperature-Based LED Current Dimming Implementation

When TSET pin is grounded and TSENSE is floated, this feature is disabled. LED current is set by RISET resistor:

Equation 6. LP8867-Q1 LP8869-Q1 eq-03-ILED.gif

where

  • VBG = 1.2 V
  • RISET is current setting resistor, kΩ
  • ILED is output current per OUTx pin, mA

When external NTC is connected, the TSENSE pin current decreases LED output current. Temperature T1 and de-rate slope are defined by external resistors as explained below.

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

Equation 7. LP8867-Q1 LP8869-Q1 eq-05-temper02.gif

TSET voltage can be calculated with Equation 8:

Equation 8. LP8867-Q1 LP8869-Q1 eq-06-temper03.gif

TSENSE pin current is calculated by Equation 9:

Equation 9. LP8867-Q1 LP8869-Q1 eq-07-temper04.gif

where

  • VDD is the bias voltage of the resistor group. It's recommended to connect with chip's internal LDO output (pin 2)

ISET pin current defined by RISET is:

Equation 10. LP8867-Q1 LP8869-Q1 form_temper01_SNVSA50.gif

For Equation 11, 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 11. ILED = (ISET_SCALED – ITSENSE ) x 2 000

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

An Excel® calculator is available for calculating the component values for a specific NTC and target thermal profile (contact TI E2E™ support forums ). Figure 17 shows an example thermal profile implementation.

LP8867-Q1 LP8869-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 17. Calculation Example