DC871A-B: 350mA Flash, 150mA Torch, 2.9 ~ 4.4V in

Demonstration circuit 871 is a low noise high current LED charge pump featuring the LTC®3215 and a cell phone camera flash LED. The board has three versions (-A, -B, -C) that are optimized separately for a short LED flash current or a lower but 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 LTC3215 the top solution for space-constrained cellular telephone camera flash solutions. The LTC3215 is very similar to the LTC3216, but with two less pins and a slightly lower maximum flash current of 700mA as opposed to
1000mA.

DC871A can be built with three AAA batteries in series in a battery pack on the back to simulate the capabilities of a typical lithium ion cellular telephone battery. The LED is turned on and off by pressing the LED ON button. Without the FLASH button pressed, the LED ON button sets the LED current to the TORCH MODE setting in the schematic. The FLASH button flashes the LED at higher current as shown in the schematic for cellular telephone camera flash operation. The FLASH only works when the LED ON button is also pressed. The FLASH button activates a MOSFET that places a second ISET resistor in parallel with the original, raising the LED current. FLASH MODE is intended to be less than one second long. Holding down the FLASH button with the LED ON can damage the LED and potentially damage the IC.

The LTC3215 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 871. In addition, the datasheets for the three LEDs must be read in order to understand the thermal and light output specifications of the LEDs. The LTC3215 is assembled in a small low profile DFN package. Proper board layout is essential for maximum thermal performance. See the datasheet section ‘Layout Considerations.