ZHCSLM3B August 2020 – May 2024 LP8864-Q1
PRODUCTION DATA
- 1
- 1 特性
- 2 應用
- 3 說明
- 4 Pin Configuration and Functions
- 5 Specifications
-
6 Detailed Description
- 6.1 Overview
- 6.2 Functional Block Diagram
- 6.3
Feature Description
- 6.3.1 Control Interface
- 6.3.2 Function Setting
- 6.3.3 Device Supply (VDD)
- 6.3.4 Enable (EN)
- 6.3.5 Charge Pump
- 6.3.6 Boost Controller
- 6.3.7 LED Current Sinks
- 6.3.8 Brightness Control
- 6.3.9
Protection and Fault Detections
- 6.3.9.1 Supply Faults
- 6.3.9.2
Boost Faults
- 6.3.9.2.1 Boost Overvoltage Faults (BSTOVPL, BSTOVPH)
- 6.3.9.2.2 Boost Overcurrent Faults (BSTOCP)
- 6.3.9.2.3 LEDSET Resistor Missing Faults (LEDSET)
- 6.3.9.2.4 MODE Resistor Missing Faults (MODESEL)
- 6.3.9.2.5 FSET Resistor Missing Faults (FSET)
- 6.3.9.2.6 ISET Resistor Out of Range Faults (ISET)
- 6.3.9.2.7 Thermal Shutdown Faults (TSD)
- 6.3.9.3 LED Faults
- 6.3.9.4 Overview of the Fault and Protection Schemes
- 6.4 Device Functional Modes
- 6.5 Programming
-
7 Application and Implementation
- 7.1 Application Information
- 7.2
Typical Applications
- 7.2.1
Full Feature Application for Display Backlight
- 7.2.1.1 Design Requirements
- 7.2.1.2
Detailed Design Procedure
- 7.2.1.2.1 Inductor Selection
- 7.2.1.2.2 Output Capacitor Selection
- 7.2.1.2.3 Input Capacitor Selection
- 7.2.1.2.4 Charge Pump Output Capacitor
- 7.2.1.2.5 Charge Pump Flying Capacitor
- 7.2.1.2.6 Output Diode
- 7.2.1.2.7 Switching FET
- 7.2.1.2.8 Boost Sense Resistor
- 7.2.1.2.9 Power-Line FET
- 7.2.1.2.10 Input Current Sense Resistor
- 7.2.1.2.11 Feedback Resistor Divider
- 7.2.1.2.12 Critical Components for Design
- 7.2.1.3 Application Curves
- 7.2.2 Application with Basic/Minimal Operation
- 7.2.3
SEPIC Mode Application
- 7.2.3.1 Design Requirements
- 7.2.3.2
Detailed Design Procedure
- 7.2.3.2.1 Inductor Selection
- 7.2.3.2.2 Coupling Capacitor Selection
- 7.2.3.2.3 Output Capacitor Selection
- 7.2.3.2.4 Input Capacitor Selection
- 7.2.3.2.5 Charge Pump Output Capacitor
- 7.2.3.2.6 Charge Pump Flying Capacitor
- 7.2.3.2.7 Switching FET
- 7.2.3.2.8 Output Diode
- 7.2.3.2.9 Switching Sense Resistor
- 7.2.3.2.10 Power-Line FET
- 7.2.3.2.11 Input Current Sense Resistor
- 7.2.3.2.12 Feedback Resistor Divider
- 7.2.3.2.13 Critical Components for Design
- 7.2.3.3 Application Curves
- 7.2.1
Full Feature Application for Display Backlight
- 7.3 Power Supply Recommendations
- 7.4 Layout
- 8 Register Maps
- 9 Device and Documentation Support
- 10Revision History
- 11Mechanical, Packaging, and Orderable Information
封裝選項
機械數據 (封裝 | 引腳)
散熱焊盤機械數據 (封裝 | 引腳)
訂購信息
6.3.8.9 Dither
The number of brightness steps when using LED output PWM dimming is equal to the 20MHz oscillator frequency divided by the LED PWM frequency (set by PWM_FSET resistor). The PWM duty cycle dither is a function the LP8864-Q1 uses to increase the number of brightness dimming steps beyond this oscillator clock limitation. The dither function modulates the LED driver output duty cycle over time to create more possible average brightness levels. The DITHER_SELECT[3:0] register bits control the level of dither, disabled, 1, 2, 3 or 4 bits using the I2C interface. By default the dither is disabled.
When the 1-bit dither is selected, to support higher brightness resolution, the width of every second PWM pulse could be increased by one LSB (one 20MHz clock period). When the 3-bit dither is selected, within a sequence of 8 PWM periods the number of pulses with increased length varies depending on the dither value: dither value 000 - all 8 pulses at default length; 001 - one of the 8 pulses is longer; 010 - two of the 8 pulses are longer, and so forth, until at 111 - seven of the 8 pulses have increased length. Figure 6-14 shows one example of PWM output dither.
Figure 6-14 PWM Dither ExampleThe dither block also helps in low brightness scenario when dimming ratio is limited by LED PWM output frequency and the LED output pulse is less than the minimum pulse width (200ns). In such scenario, the dither block will skip some of the PWM pulses to reduce the brightness further, enabling high dimming ratio. The end result is that the LED PWM frequency is reduced as more and more minimum pulses are skipped or dithered out. At the same time, dither block will also guarantee that the minimum LED PWM frequency is not less than 152Hz to ensure no brightness flickering. Figure 6-15 shows how the dither works in low brightness scenario.
Figure 6-15 Minimum Brightness Dither
Example