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

3.3 Solution: Override String Auto-Detection

To avoid the wrong phase shift or fault misreport caused by string auto-detection, a method to override the string auto-detection is provided. You can access the LED_AUTO_DETECT register (an internal register not specified in datasheet) to override string auto-detection and manually set the string configuration through I2C/SPI. Note that this register needs to be overridden during start-up. Use the following sequence:

  1. Power up system with both VDD and VDDIO supplied
  2. Wait 2 ms after VDD voltage > 2.8 V
  3. Set LED_AUTO_OVERRIDE to 1 and write <new data> to LED_STRING_CONF in 0x28C to override the LED_AUTO_DETECT register (see Table 2)
  4. Write other registers for other configuration (if needed)
  5. Pull EN high

Table 2. LED_AUTO_DETECT Register: Address: 0x28C

Bit Field Description Type Reset
15-4 Reserved Reserved (Don’t change) R/W 810h
3 LED_AUTO_
OVERRIDE		 0h = String configuration is auto detected
1h = String configuration is overriden by register bits LED_STRING_CONF		 R/W 0h
2-0 LED_STRING_CONF 0h = 6 separate strings
1h = 5 separate strings
2h = 4 separate strings
3h = 3 separate strings
4h = 2 separate strings
5h = outputs connected in groups of 3 to drive 2 strings
6h = outputs connected in groups of 2 to drive 3 strings
7h = all outputs connected together to drive one string		 R/W 0h

CAUTION

The LP8863-Q1 device 7-bits I2C slave address is 0x2E for 0x28C register if SS_ADDRSEL pin is connected to GND. Or 7-bits I2C slave address is 0x3E for 0x28C register if SS_ADDRSEL pin is biased by VDDIO.