STCF01_06 Datasheet, PDF(8/16 Page) STMicroelectronics – Step-up converter for cell phone camera flash LEDs

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STCF01_06 Datasheet, PDF (8/16 Pages) STMicroelectronics – Step-up converter for cell phone camera flash LEDs

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Detailed description

6 Detailed description

STCF01

The STCF01 white Led boost converter drives from two up to four white LEDs with a constant

current. It needs few external components: two ceramic capacitors (CI=2.2ÂµF CO=4.7ÂµF), one

inductor L=10ÂµH and one schottky diode. The device works with a minimum VI=2.6V, and it has

an Over Voltage Protection on the output guaranteed at minimum value equal to 17V. This

value ensures proper operation with a maximum of four White LEDs in series. In the worst case

of VI=2.6V at VOVP=8V (typical value of two LEDs) it is possible to obtain IO=270mA, while at

VOVP=11V (typical value of three LEDs) it is possible obtain IO=180mA (Figure 4). The

maximum IO current is limited by inductor peak current internally set at Typ 1.2A. This feature

allows for a longer battery life as it reduces intensive use of the flash. The SEL pin allows

selection of high and low current values flowing on the White LEDs.

The two current values are set through external resistors RHC and RLC according to the

following formula:

ILED(FLASH) = 2100 * (VI - VHC) / RHC

ILED(TORCH) = 2400 * (VI - VLC) / RLC

A High logic level on SHDN pin puts the device in shutdown mode; if it is held at LOW the flash

or torch mode is activated. When the SHDN pin is LOW the device provides the requested

current in less than 200Âµs (see TURN ON TIME plot). This fast turn-on time makes the device

suitable for single shoot and multiple shoot operation modes.

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