ZHCSCK8G May 2014 – October 2017 LP8860-Q1
PRODUCTION DATA.
The <EXT_TEMP_COMP_EN> EEPROM bit enables the LED current limitation mode. The principle of current limitation is shown in Figure 31.
When LED temperature reaches <EXT_TEMP_LEVEL_LOW[3:0]> level, the device automatically tries to reduce LED average current step-by-step by 3.125% from maximum brightness value. Step time is defined by <EXT_TEMP_PERIOD[4:0]> EEPROM bits. If temperature continues to increase and reaches <EXT_TEMP_LEVEL_HIGH[3:0]> level, the device shuts down the LEDs and generates a fault condition. The LEDs are turned on automatically when the temperature is below the <EXT_TEMP_LEVEL_LOW[3:0]> level. Otherwise, if after one or more steps the temperature drops down below <EXT_TEMP_LEVEL_LOW[3:0]>, brightness increases with the same step time until it reaches the original level. The LP8860-Q1 uses PWM duty reduction to reduce LED current. The device detects external NTC resistor availability, and the <TEMP_RES_MISSING> flag is set, if the NTC sensor is missing (resistance is 2 MΩ or more).