2 LP8863-Q1 LED String Auto-Detection Mechanism

Figure 1 shows the LP8863-Q1 string auto-detection flow.

When VDD is powered up, the device automatically injects 1 mA current on LED0 pin in order to check whether using multi-string configuration.

• If only LED0 and LED1 are detected beyond 1 V, which indicates LED0 and LED1 pins are tied together, the device will set AUTO_LED_STRING_CFG = 5h (outputs connected in groups of 2 to drive 3 strings)
• If only LED0, LED1 and LED2 are detected beyond 1 V, which indicates LED0, LED1 and LED2 pins are tied together, the device will set AUTO_LED_STRING_CFG = 6h (outputs connected in groups of 3 to drive 2 strings)
• If all LEDx are detected beyond 1 V, which indicates all LEDx pins are tied together, the device will set AUTO_LED_STRING_CFG = 7h (all outputs connected together to drive one string)

If none of above situations meets, the device automatically injects 1 mA current on every LEDx pin in order to check whether using separate-string configuration.

• If only LED0 and LED1 are detected beyond 1 V, which indicates LED2 to approximately LED5 pins are tied to ground, the device will set AUTO_LED_STRING_CFG = 4h (2 separate strings)
• If LED0, LED1 and LED2 are detected beyond 1V, which indicates LED3 ~ LED5 pins are tied to ground, the device will set AUTO_LED_STRING_CFG = 3h (3 separate strings)
• If only LED0, LED1, LED2 and LED3 are detected beyond 1 V, which indicates LED4 and LED5 pins are tied to ground, the device will set AUTO_LED_STRING_CFG = 2h (4 separate strings)
• If only LED0, LED1, LED2, LED3 and LED4 are detected beyond 1 V, which indicates LED5 pin is tied to ground, the device will set AUTO_LED_STRING_CFG = 1h (5 separate strings)
• If all LEDx are detected beyond 1 V, which indicates no LEDx pin is tied to ground, the device will set AUTO_LED_STRING_CFG = 0h (6 separate strings)

If none of above situations meets, which means the string detection does not match one of 8 valid configurations, the device automatically defaults to AUTO_LED_STRING_CFG = 0h (6 separate strings) and alarms invalid LED string fault.

Figure 2(a) demonstrates a normal start-up of LP8863-Q1. Figure 2(b) shows an enlarged portion of LED string detection of Figure 2(a). Figure 2(c) displays the phase shift of each LEDx.