STCF02

Detailed operating description

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Detailed operating description

6.1

Introduction

The STCF02 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 constant switching frequency of 1.8MHz typ. It provides

an output voltage down to 2.5V and up to 5.1 V, from a single cell 2.7 V to 5.5 V lithium-ion battery. The

flash current is adjustable from 100mA to 600mA for the input voltage range from 2.7V to 4.5V. Torch

current is adjustable from 25mA to 250mA. The device also includes a medium flash mode with the

current set between the 25% of flash current and flash current. The device contains a pin for connection

of NTC which senses the temperature of the LED.

6.2

Buck-Boost converter

(see

Figure 2). Depending on the forward voltage of the Flash LED, the device can automatically change

the operation mode between buck (step down) and boost (step up) mode. Three case can occur:

6.3

Flash mode

To select Flash mode the Enable pins have to be connected as follows: EN1=1, EN2=1, EN3=0.

The STCF02 operates continuously to supply maximum current to the flash LED (up to 600 mA).

For a flash current programmed at 600mA, the sensing resistor is equal to 0.27

Ω.

During this operation mode the MOS Switch between FB1 and RTBY pins is closed.

If the EN3 is forced to High during Flash mode operation, the current is reduced to that of Torch mode.

Such reduction of input power during transition from Flash to Torch mode is achieved within less than

30µs. The NTC divider for measuring LED temperature is active.