STCF06TBR datasheet(13/33 Pages) STMICROELECTRONICS

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Detailed description

STCF06

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Detailed description

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

Buck-boost converter

The regulation of the PWM controller is done by sensing the current of the LED through

external sensing resistors (RFL and RTR, 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 (VO > VBAT): this configuration is used in most of the

cases, as the output voltage VO = VfLED + ILED x RFL is higher than VBAT; Buck region (VO <

VBAT); Buck / Boost region (VO ~ VBAT).

7.3

Logic pin description

7.3.1

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.

7.3.2

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.

7.3.3

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,

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