DC805A: 200mA @ 5.1V Max, 2.9 ~ 4.4Vin, Torch/Flash

Demonstration circuit 805 is a low noise high current LED charge pump featuring the LTC®3216 and the LXCL-PWF1 Lumileds Luxeon Flash. The board is optimized for 800mA 300ms LED flash current or 200mA constant LED torch current with a single lithium ion battery input voltage range of 2.9V to 4.4V or three AAA batteries in series. The lithium ion battery input voltage range, high LED flash current and separate torch mode current setting, internal charge pump switches, inductor-less solution, minimal external components, and simple design makes the LTC3216 is the top solution for space-constrained cellular telephone camera flash solutions.

DC805 comes with three AAA batteries in series to simulate the capabilities of a typical lithium ion cellular telephone battery. This portable board is turned on and off by pressing the ON/OFF button. A TORCH button turns the LED on at 200mA for cellular telephone video recording. The FLASH button flashes the LED at 800mA for 300ms for cellular telephone camera flash operation. The buttons control the state of the PIC microcontroller IC that is programmed with DC805 software. The PIC keeps the LED from being flashed constantly, preventing overheating and burnout. 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 LTC3216 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 805. In addition, Lumileds Luxeon Flash datasheet featuring LXCL-PWF1 (www.lumileds.com) must be read to understand thermal and LED current constraints for varying flash current pulse-widths and intensity.

The LTC3216 is assembled in a small low profile DFN package. Proper board layout is essential for maximum thermal performance. See the datasheet section Layout Considerations.