STCF03ITBR datasheet(21/33 Pages) STMICROELECTRONICS

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Description of internal registers

STCF03I

21/33

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.

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 13)

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 RFL and RTR. (Figure 13)

Note:

LED current values refer to RFL=0.27 Ω, RTR=1.8 Ω

Table 11.

Dimming register

DIM_REG

(write mode)

MSB

LSB

SUB ADD=01

TDIM_3

TDIM_2

TDIM_1

TDIM_0

FDIM_3

FDIM_2

FDIM_1

FDIM_0

Power ON,

SHUTDOWN MODE

RESET Value

0000

Figure 13.

Flash and Torch current vs. dimming value

Current Step Coefficient - 1.19

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