STCF06 Datasheet, PDF (15/33 Pages) STMicroelectronics – 1.5 A white LED driver with I²C interface

Detailed description
STCF06
by setting the PWR_ON bit; from flash operation by resetting the TRIG pin or the TRIG_EN
bit or automatically from flash operation when the time counter reaches zero; from torch
operation by resetting the TCH_ON bit. The device automatically enters this mode also
when an overload or an abnormal condition has been detected during flash or torch
operation (Table 16: Status register details:).
7.7
Single or multiple flash using external (µP) temporization
To avoid the I²C bus time latency, it is recommended to use the dedicated TRIG pin to define
the flash duration (hard-triggering). The TRIG_EN bit of CMD_REG should be set before
starting each flash operation, because it could have been reset automatically in the previous
flash operation. The flash duration is determined by the pulse length that drives the TRIG
pin. As soon as the flash is activated, the system needs typically 1.2 ms to ramp up the
output current on the Power LED. The internal time counter will time-out flash operation and
keep the LED dissipated energy within safe limits in case of Software deadlock; FTIM
register has to be set first, either in Stand-by or in ready mode. Multiple flashes are possible
by strobing the TRIG pin. Time out counter will cumulate every flash on-time until the
defined time out is reached unless it is reloaded by updating the CMD_REG. After a single
or multiple flash operations are timed-out, the device automatically goes into Ready mode
by resetting the TRIG_EN bit, and also resets the F_RUN bit. The ATN pin is pulled down to
inform the µP that the STAT_REG has been updated.
7.8
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.
7.9
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
STCF06 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 be kept High (logic level or wired to V_BAT) and the flash can be started by
setting the FTIM and the TRIG_EN through I²C (both are located in 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.
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