When the ambient light was dimmed, LX1970 can automatically open the LCD’s backlight, so the white LED light. Automatic brightness control circuit as shown. Using resistors R1 and R2 can be set to control the minimum and maximum brightness. Changes in the capacity of the capacitor C adjustable response time and can remove 50Hz power interference. LX1970 by 3.3 ~ 5V power supply. End only when the SRC, SNK side should be left open. Assumptions required 0.25 ~ 1.25V output voltage to drive white LED, 0.25V represents the minimum LED brightness, 1.25V represents the maximum brightness.
Circuit design should first determine the ratio between R1 and R2, the formula is:
Then LX1970 brightness at a given maximum output current (ISRCmax) to calculate the R2 values. Assumed ISRCmax = 50µA, with R2 values of the following formula can be obtained:
Calculated R2 = 25kO, get R1 = 275kO.