STCF05 Datasheet, PDF (26/33 Pages) STMicroelectronics – High power white LED driver with I²C interface

Detailed description
10 Detailed description
STCF05
10.1
Power ON reset
This mode is initiated by applying a supply voltage above the VPW_ON RESET threshold
value. An internal timing (~ 1 µs) defines the duration of this status. The logic blocks are
powered, but the device doesn't respond to any input. The registers are reset to their default
values, the ATN and SDA pins are in high impedance, the I²C slave address is internally set
by reading the ADD pin configuration. After the internally defined time has elapsed, the
STCF05 automatically enters the shutdown mode.
10.2
Shutdown, shutdown with NTC
In this mode only the I²C interface is alive, accepting I²C commands and register settings.
The device enters this mode: automatically from Power ON reset status or by resetting the
PWR_ON bit from other operation modes. Power consumption is at the minimum (1 µA typ)
if NTC is not activated (NTC_ON=0). If PWR_ON and NTC_ON is set, the T1 is switched
ON (see the block diagram), allowing the microprocessor to measure the LED temperature
through its A/D converter.
10.3
Ready mode
In this mode all internal blocks are turned ON, but the DC-DC converter is disabled and the
White LED is disconnected. The NTC circuit can be activated to monitor the temperature of
the LED and I²C commands and register settings are allowed to be executed immediately.
Only in this mode the auxiliary LED is operational and can be turned ON and set at the
desired brightness using the AUX REGISTER.
The device enters this mode:
● from standby 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).
10.4
Single or multiple flash using external (microprocessor)
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 standby or in ready mode. Multiple flashes are possible
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Doc ID 15257 Rev 4