STCF03I Datasheet, PDF (21/33 Pages) STMicroelectronics – High power white LED driver with I2CTM interface

Description of internal registers
STCF03I
8.5
FTIM_0~3
This 4-bits register defines the maximum Flash duration. It is intended to limit the energy
dissipated by the LED to a maximum safe value or to leave to the STCF03I the control of the
Flash duration during normal operation. Values from 0~15 correspond to 0~1.5 s (100 ms
steps). The timing accuracy is related to the internal oscillator frequency that clocks the
Flash Time Counter (+/-20%, TBD). Entering Flash mode (either by soft or hard triggering)
activates the Flash Time Counter, which begins counting down from the value loaded in the
F_TIM register. When the counter reaches zero, Flash mode is stopped by resetting
TRIG_EN bit, and simultaneously the ATN pin is set to true (LOW) to alert the µP that the
maximum time has been reached. FTIM value remains unaltered at the end of the count.
Table 11. Dimming register
DIM_REG
(write mode)
MSB
SUB ADD=01
TDIM_3
Power ON,
0
SHUTDOWN MODE
RESET Value
TDIM_2
0
TDIM_1
0
TDIM_0
0
FDIM_3
0
FDIM_2
0
FDIM_1
0
LSB
FDIM_0
0
8.6
TDIM_0~3
These 4 bits define the LED current in Torch mode with 16 values fitting an exponential law.
Max Torch current value is 25% of max Flash current. (Figure 12)
8.7
FDIM_0~3
These 4 bits define the LED current in Flash mode with 16 values fitting an exponential law.
The Max value of the current is set by the external resistors R_FL and R_TR. (Figure 12)
Figure 12. Flash and Torch current vs. dimming value
Current Step Coefficient - 1.19
Note:
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LED current values refer to R_FL=0.27 Ω, R_TR=1.8 Ω