ZHCSCK8G May 2014 – October 2017 LP8860-Q1
PRODUCTION DATA.
When an external resistor for maximum current control is used, current dimming for LED current can be used also. In this case LED current can be de-rated when ambient temperature is high. This option must be enabled by <EXT_TEMP_I_DIMMING_EN> and <EXT_TEMP_COMP_EN> EEPROM bits.
Knee point and slope are defined by <EXT_TEMP_MINUS[1:0]> and <EXT_TEMP_GAIN[3:0]> EEPROM bits respectively. LED shutdown temperature is defined by <EXT_TEMP_LEVEL_HIGH[3:0]> bits. Serial and parallel resistors R1 and R2 affect the slope and knee point and can be used for the thermal curve adjustment and NTC linearization.
Figure 35 and Figure 36 show the block diagrams for current dimming.
Current dimming by external NTC sensor for 150-mA scale can be defined by formulas:
ITEMP cannot be negative; if ITEMP< 0, then ITEMP must be 0.
where