DC843A: 3A @ 42V Max, 2.5 ~ 24V in

Demonstration circuit 843 is a high current boost LED driver featuring the LT®3479 and the AOT 3218 Flash LED. The board is optimized for 700mA 300ms LED flash current or 150mA constant LED torch current with a single lithium ion battery input voltage range of 2.7V to 4.5V. The lithium ion battery input voltage range, high LED flash current and separate torch mode current setting, internal NPN power switch, small inductor solution, minimal external components, and simple design makes the LT3479 an excellent solution for space-constrained camera flash solutions with high battery capability.

Demonstration circuit 843 is turned on and off by pressing the ON/OFF button. A TORCH button turns the LED on at 150mA for cellular telephone or other video recording. The FLASH button flashes the LED at 700mA for 300ms for camera flash operation. The buttons control the state of the PIC microcontroller IC that is programmed with DC843A software. The PIC keeps the LED from being constantly in flash mode, preventing overheating and failure of the LED. The PIC also controls the flash time. When no buttons are pressed for a short time, the PIC turns off and the circuit enters low-power mode for battery-life preservation.

A red/green LED indicates the state of the PIC. The LED is ready to flash or torch if the state indicator is blipping green. If the indicator is not on, the PIC is turned off. For a brief time after the flash has occurred, the state-indicator LED is red, indicating that another flash cannot happen, even if the button is pressed, until the red LED is off and the green LED is blipping again.

The LT3479 datasheet gives a complete description of the part, operation and applications information. The datasheet must be read in conjunction with this Quick Start Guide for demonstration circuit 843. In addition, Advanced Optoelectronic Technology’s datasheet featuring AOT 3218 http://www.aot.com.tw) must be read to understand thermal and LED current constraints for varying flash current pulse-widths and intensity. The LT3479 is assembled in a small low profile DFN package. Proper board layout is essential for maximum thermal performance. See the datasheet section Layout Considerations.