QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 843
HIGH CURRENT BOOST LED DRIVER
LT3479
DESCRIPTION
Demonstration circuit 843 is a high current boost
LED driver featuring the LT®3479 and the AOT 3218
Flash LED. The board is optimized for 700mA 300ms
LED flash current or 150mA constant LED torch cur-
rent with a single lithium ion battery input voltage
range of 2.7V to 4.5V. The lithium ion battery input
voltage range, high LED flash current and separate
torch mode current setting, internal npn power
switch, small inductor solution, minimal external
components, and simple design makes the LT3479 an
excellent solution for space-constrained camera flash
solutions with high battery capability.
Demonstration circuit 843 is turned on and off by
pressing the ON/OFF button. A TORCH button turns
the LED on at 150mA for cellular telephone or other
video recording. The FLASH button flashes the LED at
700mA for 300ms for camera flash operation. The
buttons control the state of the PIC microcontroller IC
that is programmed with DC843A software. The PIC
keeps the LED from being constantly in flash mode,
preventing overheating and failure of the LED. 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 preser-
vation.
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 oc-
curred, 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 LT3479 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 843. In addition,
Advanced Optoelectronic Technology’s datasheet fea-
turing AOT 3218 (http://www.aot.com.tw) must be
read to understand thermal and LED current con-
straints for varying flash current pulse-widths and
intensity. The LT3479 is assembled in a small low
profile DFN package. Proper board layout is essential
for maximum thermal performance. See the data-
sheet section ‘Layout Considerations’.
Design files for this circuit board are available. Call
the LTC factory.
LT is a trademark of Linear Technology Corporation
QUICK START PROCEDURE
Demonstration circuit 843 is easy to set up to evalu-
ate the performance of the LT3479. Follow the proce-
dure below:
1.
Connect 2.7-4.5V input voltage as shown in Figure
4.
Press ‘TORCH’ to observe constant 150mA LED
light for recording video.
5.
Press ‘TORCH’ to turn off the 150mA video mode.
6.
Press ‘ON/OFF’ to turn off the circuit or let the cir-
1 to VIN and GND terminals.
2.
If the state-indicator LED is not blipping green,
cuit turn off by not pressing any buttons for ap-
proximately 10 seconds.
press the ON/OFF button to turn on the circuit.
3.
Press ‘FLASH’ to observe a 300ms, 700mA camera
flash on the AOT 3218 LED.
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