QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 871 LOW NOISE HIGH CURRENT LED CHARGE PUMP LTC3215 DESCRIPTION Demonstration circuit 871 is a low noise high current button flashes the LED at higher current as shown in LED charge pump featuring the LTC 3215 and a cell the schematic for cellular telephone camera flash phone camera flash LED. The board has three ver- operation. The FLASH only works when the LED ON sions (-A, -B, -C) that are optimized separately for a button is also pressed. The FLASH button activates a short LED flash current or a lower but constant LED MOSFET that places a second ISET resistor in paral- torch current with a single lithium ion battery input lel with the original, raising the LED current. FLASH voltage range of 2.9V to 4.4V or three AAA batteries MODE is intended to be less than one second long. in series. The lithium ion battery input voltage range, Holding down the FLASH button with the LED ON high LED flash current and separate torch mode cur- can damage the LED and potentially damage the IC. rent setting, internal charge pump switches, induc- The LTC3215 datasheet gives a complete description torless solution, minimal external components, and of the part, operation and applications information. simple design makes the LTC3215 the top solution The datasheet must be read in conjunction with this for space-constrained cellular telephone camera Quick Start Guide for demonstration circuit 871. In flash solutions. The LTC3215 is very similar to the addition, the datasheets for the three LEDs must be LTC3216, but with two less pins and a slightly lower read in order to understand the thermal and light maximum flash current of 700mA as opposed to output specifications of the LEDs. The LTC3215 is 1000mA. assembled in a small low profile DFN package. DC871A can be built with three AAA batteries in se- Proper board layout is essential for maximum ther- ries in a battery pack on the back to simulate the ca- mal performance. See the datasheet section Layout pabilities of a typical lithium ion cellular telephone Considerations. battery. The LED is turned on and off by pressing the Design files for this circuit board are available. LED ON button. Without the FLASH button pressed, Call the LTC factory. the LED ON button sets the LED current to the , LTC and LT are registered trademarks of Linear Technology Corporation. TORCH MODE setting in the schematic. The FLASH QUICK START PROCEDURE Demonstration circuit 871 is easy to set up to evalu- extremely low-ESR ceramic input capacitor to ring to ate the performance of the LTC3215. Follow the pro- twice its DC value. See Application Note 88 for more cedure below: details. NOTE: Make sure that the input voltage does not ex- 1. Connect 2.9V to 4.4V input power supply to the ceed 5.5V if a source other than the three AAA batter- VIN and GND terminals on the PCB or three AAA ies is used. batteries in a battery pack that is connected to the + and terminals on the PCB. NOTE: If batteries are not used, do not hot-plug the input voltage terminals VIN (+) and GND (-). The ab- 2. Press LED ON to turn on the LED in torch mode. solute maximum voltage on VIN is 5.5V and hot- 3. Briefly (less than 1 second) Press FLASH to ob- plugging a power supply through wire leads to the serve a higher cell phone camera flash LED cur- demonstration circuit can cause the voltage on the rent. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 871 LOW NOISE HIGH CURRENT LED CHARGE PUMP Figure1. Proper Measurement Equipment Setup 2