SNVA958 April   2020 LP8863-Q1

 

  1.   LP8863-Q1 Automatic String Detection Deep Dive
    1.     Trademarks
    2. 1 Introduction
    3. 2 LP8863-Q1 LED String Auto-Detection Mechanism
    4. 3 Application Issue
      1. 3.1 Misuse Invalid LED String Configuration
      2. 3.2 Power Off Then On Immediately
      3. 3.3 Solution: Override String Auto-Detection

1 Introduction

The LP8863-Q1 device is an automotive 6-channel backlighting LED driver, which defaults to phase shift mode. When the device is powered on, the string configuration is automatically detected and the phases of each channel configured. For example, if four strings are connected, the LED outputs are phase shifted by 90° (= 360 / 4); if 6 strings are connected, the LED outputs are phase shifted by 60° (=360/6). The LED strings are always appropriately phase shifted for their string configuration. This reduces the ripple of the boost output, and increases the load frequency which can move potential capacitor noise above the audible band.

The string configurations in Table 1 are valid configurations for auto detection. Any invalid configurations are NOT allowed to be used. The detected configuration can be read from AUTO_LED_STRING_CFG in AUTO_DETECT_DIAGNOSTICS register.

Table 1. LP8863-Q1 Valid LED String Configurations

Configuration LED0 LED1 LED2 LED3 LED4 LED5 Detected LED String Configuration
(AUTO_LED_STRING_CFG)		 Phase Shift
6 channels 150 mA 150 mA 150 mA 150 mA 150 mA 150 mA 0h = 6 separate strings 60°
5 channels 150 mA 150 mA 150 mA 150 mA 150 mA GND 1h = 5 separate strings 72°
4 channels 150 mA 150 mA 150 mA 150 mA GND GND 2h = 4 separate strings 90°
3 channels 150 mA 150 mA 150 mA GND GND GND 3h = 3 separate strings 120°
2 channels 150 mA 150 mA GND GND GND GND 4h = 2 separate strings 180°
3 channels 300 mA 300 mA 300 mA 5h = outputs connected in groups of 3 to drive 2 strings 120°
2 channels 450 mA 450 mA 6h = outputs connected in groups of 2 to drive 3 strings 180°
1 channel 900 mA 7h = all outputs connected together to drive one string None