DC871A-B - LINEAR TECHNOLOGY - Datasheet.Directory

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

LED charge pump featuring the LTC®3215 and a cell

phone camera flash LED. The board has three ver-

sions (-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 cur-

rent setting, internal charge pump switches, induc-

torless 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 se-

ries in a battery pack on the back to simulate the ca-

pabilities 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 paral-

lel 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 ther-

mal performance. See the datasheet section ‘Layout

Considerations’.

Design files for this circuit board are available.

Call the LTC factory.

, LTC and LT are registered trademarks of Linear Technology Corporation.

QUICK START PROCEDURE

Demonstration circuit 871 is easy to set up to evalu-

ate the performance of the LTC3215. Follow the pro-

cedure below:

NOTE:

Make sure that the input voltage does not ex-

ceed 5.5V if a source other than the three AAA batter-

ies is used.

NOTE:

If batteries are not used, do not hot-plug the

input voltage terminals VIN (+) and GND (-). The ab-

solute maximum voltage on VIN is 5.5V and hot-

plugging a power supply through wire leads to the

demonstration circuit can cause the voltage on the

extremely low-ESR ceramic input capacitor to ring to

twice its DC value.

See Application Note 88 for more

details.

Connect 2.9V to 4.4V input power supply to the

VIN and GND terminals on the PCB or three AAA

batteries in a battery pack that is connected to the

+ and – terminals on the PCB.

Press LED ON to turn on the LED in torch mode.

Briefly (less than 1 second) Press FLASH to ob-

serve a higher cell phone camera flash LED cur-

rent.