AN3223 Datasheet, PDF (21/29 Pages) STMicroelectronics – Driver for double flash LED with I²C interface

AN3223
8
The light sensor
The light sensor
The light sensor is an optional feature which optimizes the FLASH duration according to the
light conditions in the flashed scene. This feature requires three external components to be
connected to the STCF04 according to Figure 12. It is recommended to connect the
collector of the phototransistor to V_REF = 1.8 V. The integrating capacitor C_INT is discharged
before every FLASH pulse. This reset takes approximately 200 µs. During the FLASH the
voltage on this capacitor increases according to the amount of light in the scene and T_FOTO,
R_LIGHT, and C_INT parameters. The values of these components must be selected according
to the final application purpose.
Figure 12. Optional light sensor feature
AM07806v1
Doc ID 17553 Rev 2
21/29