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

Power Off Then On Immediately

The LP8863-Q1 device uses the LEDx pin voltage to detect the string configuration. If the device powered off then on immediately, the boost output is not fully discharged, causing LEDx pin is not fully discharged, the string auto-detection may work improperly like Application Issue 1.

For example, if power off then on immediately, the 6 separate strings mode could be detected as all outputs connected together mode (AUTO_LED_STRING_CFG = 7h) since all LEDx pin voltage is beyond 1 V, as shown in Figure 4(a) and Figure 4(b). There will be no phase shift but should be 60°. For the solution, see Section 3.3.

(a) LP8863-Q1 String Detection Flow
(b) LED String Detection Waveform
Figure 4. LP8863-Q1 Power Off Then On Immediately (use 6 separate strings)