STCF06 Datasheet, PDF (13/33 Pages) STMicroelectronics – 1.5 A white LED driver with I²C interface

Detailed description
7
Detailed description
STCF06
7.1
Introduction
The STCF06 is a buck-boost converter, dedicated to power and control the current of a
power white LED in a camera cell phone. The device operates at a typical constant
switching frequency of 1.8 MHz. It regulates the LED current up to 1.5 A and supports LED
with forward voltage ranging from 2.5 V to 5.0 V. The input voltage supply range from 2.7 V
to 5.5 V allows operation from a single cell Lithium-Ion battery. The I²C bus is used to control
the device operation and for diagnostic purposes. The current in torch mode is adjustable up
to 370 mA. Flash mode current is adjustable up to 1500mA for an input voltage higher than
3.5 V, 1300 mA for an input voltage of 3.0 V at least and 1000 mA when the input voltage is
2.7 V. The Aux LED current can be adjusted from 0 to 20 mA. The device uses an external
NTC resistor to sense the temperature of the white LED. These two last functions may not
be needed in all applications, and in these cases the relevant external components can be
omitted.
7.2
7.3
7.3.1
7.3.2
7.3.3
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Buck-boost converter
The regulation of the PWM controller is done by sensing the current of the LED through
external sensing resistors (R_FL and R_TR, see application schematic). Depending on the
forward voltage of the flash LED, the device automatically can change the operation mode
between buck (step down) and boost (step up) mode.
Three cases can occur: Boost region (V_O > V_BAT): this configuration is used in most of the
cases, as the output voltage V_O = V_fLED + I_LED x R_FL is higher than V_BAT; Buck region (V_O <
V_BAT); Buck / Boost region (V_O ~ V_BAT).
Logic pin description
SCL, SDA pins
These are the standard clock and data pins as defined in the I²C bus specification. External
pull-up is required according to I²C bus specifications. The recommended maximum voltage
of these signals should be 3.0 V.
TRIG pin
This input pin is internally AND-ed with the TRIG_EN bit to generate the internal signal that
activates the flash operation. This gives to the user the possibility to accurately control the
flash duration using a dedicated pin, avoiding the I²C bus latencies (hard-triggering). No
internal pull-up nor pull-down is provided.
ATN pin
This output pin (open-drain, active LOW) is provided to better manage the information
transfer from the STCF06 to the µP. Because of the limitations of a single master I²C bus
configuration, the µP should regularly poll the STCF06 to verify if certain operations have
been completed, or to check diagnostic information. Alternatively, the µP can use the ATN
pin to be advised that new data are available in the STAT_REG, thus avoiding continuous
polling. Then the information can be read in the STAT_REG by a read operation via I²C that,