DEMO CIRCUIT 875B
QUICK START GUIDE
LTC3454EDD
High Efficiency Buck-Boost Flash LED Driver
DESCRIPTION
Demonstration circuit 875 is a high efficiency buck-
boost flash LED driver featuring the LTC3454EDD. The
board has two circuits optimized for different applica-
tions: a small footprint solution featuring 350mA, 300ms
LED flash current or 150mA constant LED torch current,
and a high current solution featuring 400 / 600 /
1000mA constant-current operation. The input voltage
range of 2.7V to 5.5V is suitable for a single Lithium-Ion
battery or three AAA batteries in series. The Li-Ion input
range, high LED flash current with separate torch mode
current setting, internal synchronous power switches,
minimal and low-profile external components, and sim-
ple design makes the LTC3454 the top solution for
highly efficient, space-constrained cellular telephone
camera flash solutions.
The high current solution is activated by depressing
momentary switches ‘EN1’ and ‘EN2’ in accordance with
the table provided on the silkscreen, or connecting the
corresponding terminals to ‘VIN’ with a jumper wire. An
LED capable of handling 1A of current, such as the
LUMILED LXHL-LW3C, will be needed to be connected
to the LED+ and LED- thru-holes. The small footprint
solution is turned on and off by pressing the ‘ON/OFF’
button. A ‘TORCH’ button turns the LED on at 150mA for
cellular telephone video recording. The ‘FLASH’ button
flashes the LED at 350mA for 300ms for cellular tele-
phone camera flash operation. The buttons control the
state of the PIC microcontroller IC that is programmed
with DC875 software. The PIC keeps the LED from being
flashed constantly, preventing overheating and burnout.
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 preserva-
tion. 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 occurred,
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.
Alternatively, the torch and flash modes can be enabled
by connecting ‘EN1’ (torch), or’ EN1’ and ‘EN2’ (flash) to
‘VIN’, as indicated in the table.
WARNING- Do not pull down the ‘ENx’ pins on the
small current solution while the PIC is active, as dam-
age to the PIC outputs may result.
WARNING- The small footprint solution LED can be
permanently damaged if the flash mode is engaged for
more than a few seconds.
The PIC control circuit may be used to control the high
current solution circuit by connecting the ‘EN1’ and
‘EN2’ pins of each solution in parallel, and applying
power to both circuits. Typical efficiency for the demo
circuits are presented in Figure 2. Higher efficiency can
be obtained by selecting larger inductors with lower
ESR.
The LTC3454 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 875. In addition the
AOT2015 datasheet (www.aot.com) must be read to un-
derstand thermal and LED current constraints for vary-
ing flash current pulse-widths and intensity. The
LTC3454 is assembled in a small low profile DFN pack-
age. Proper board layout is essential for maximum
thermal performance. See the datasheet section ‘Layout
Considerations’.
Design files for this circuit board are available. Call
the LTC factory.
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DEMO CIRCUIT 875B
QUICK START GUIDE
LTC is a trademark of Linear Technology Corporation
Table 1. Performance Summary (T
A
= 25°C)
PARAMETER
Minimum Input Voltage
Maximum Input Voltage
Maximum (Guaranteed) Output Voltage
Output Current I
OUT
– small footprint solution
Output Current I
OUT
– high current solution
Maximum Output Voltage
Typical Output Ripple V
OUT
Typical Output Regulation
Nominal Switching Frequency
Efficiency
V
IN
= 4.2V, I
OUT
= 150mA
V
IN
= 4.2V, I
OUT
= 1000mA
V
IN
= 4.2V, I
OUT
= 1.0A (20MHz BW)
Line
I
L
= 1A
V
IN
= 2.7V to 5.5V
V
IN
= 2.7V to 5.5V
CONDITION
VALUE
2.7V
5.5V
4.95V
150 / 200 / 350mA
400 / 600 / 1000mA
4.9V
10mV
P–P
±0.5%
1.0MHz
92% Typical
86% Typical
QUICK START PROCEDURE
Demonstration circuit 875 is easy to set up to evaluate
the performance of the LTC3454EDD. Refer to Figure 1
for proper measurement equipment setup and follow
the procedure below:
1.
2.
SMALL FOOTPRINT SOLUTION:
5.
If the state-indicator LED, LED2, is not blipping
green, press the ‘ON/OFF’ button to turn on the cir-
cuit.
6.
7.
8.
9.
Preset a DC source capable of 5.5V at 2.5A to 4V.
Connect a high current LED capable of handling 1A
of current to the LED+ and LED- thru-holes as
shown on Figure 1.
With power off, connect the input power supply to
‘VIN’ and ‘GND’ of the circuit solution of interest.
Turn on the power at the input. The input voltage
may be varied between 2.7V and 5.5VDC.
NOTE:
Make
Press ‘FLASH’ to observe a 300ms, 350mA camera
flash.
Press ‘TORCH’ to observe a constant 150mA LED
light for recording video.
Press ‘TORCH’ to turn off the 150mA video mode.
Press ‘ON/OFF’ to turn off the circuit or let the cir-
cuit turn off by not pressing any buttons for ap-
proximately 10 seconds.
the torch and flash modes can be en-
abled by connecting ‘EN1’ (torch), or ‘EN1’ and
‘EN2’ (flash) to ‘VIN’, as indicated in the table.
3.
4.
sure the input voltage does not exceed
5.5V. The schottky diodes, D1 for the small footprint
solution and D2 for the high current solution, were
added for applications in which VIN is greater than
4.5V.
10.
Alternatively,
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