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
extremely low-ESR ceramic input capacitor to ring to
twice its DC value.
See Application Note 88 for more
details.
1.
sure that the input voltage does not ex-
ceed 5.5V if a source other than the three AAA batter-
ies is used.
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
NOTE:
If
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.
2.
3.
1
PCB Design
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