STCF03I Datasheet, PDF (26/33 Pages) STMicroelectronics – High power white LED driver with I2CTM interface

Detailed description
STCF03I
9.5
External (µP) temporization using TRIG_EN bit
Even if it is possible, it is not recommended to use the TRIG_EN bit to start and stop the
Flash operation, because of I²C bus latencies: this would result in inaccurate Flash timing.
Nevertheless, if this operation mode is chosen, the TRIG pin has to be kept High (logic level
or wired to V_BAT), leaving the whole flash control to the I²C bus. Also in this operation mode
the Time Counter will Time-out Flash operation and keep the energy dissipated by the LED
within safe limits in case of SW deadlock.
9.6
Single Flash using internal temporization
Flash triggering can be obtained either by TRIG pin (hard-triggering) or by I²C commands
(soft-triggering). The first solution is recommended for an accurate start time, while the
second is less accurate because of the I²C bus time latency. Stop time is defined by the
STCF03I internal temporization and its accuracy is determined by the internal oscillator. For
hard-triggering, it is necessary to set the TRIG_EN bit in advance. For soft-triggering, the
TRIG pin has to
setting the FTIM
be kept
and the
High (logic level or
TRIG_EN through
Iw²Cire(dbotothVa^Bre^ATl)ocaantdedthien
Flash can be started by
the CMD REG). There is
a delay time between the moment the Flash is triggered and when it appears. This delay is
caused by the time necessary to charge up the output capacitor, which is around 1.2 ms
depending on battery voltage and output current value. Once triggered, the flash operation
will be stopped when the Time Counter reaches zero. As soon as the Flash is finished, the
F_RUN bit is reset, the ATN pin is pulled down for 11 µs to inform the µP that the STAT_REG
has been updated and the device goes back to Ready mode. If it is necessary to make a
Flash longer than the internal timer allows or a continuous Flash, then the FTIM must be
reloaded through I²C bus every time, before the internal timer reaches zero. For example: To
get a continuous FLASH, set FTIM to 1.5 s and every 1 s reload the CMD_REG.
9.7
Multiple Flash using internal temporization
This operation has to be processed as a sequence of single flashes using internal
temporization starting from hard or soft triggering. Since the TRIG_EN bit is reset at the end
of each flash, it is necessary to reload the CMD_REG to start the next one.
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