QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 773
SYNCHRONOUS 1MHZ LUXEON III WHITE LED DRIVER
1
LTC3441 & LTC2050
DESCRIPTION
Demonstration circuit 773 is a synchronous buck-boost
1MHz Luxeon III white LED driver featuring the LTC3441
and LTC2050. The board is optimized for 3.9V LED for-
ward voltage output at 1000mA load current and a single
lithium-ion input voltage range of 3V to 4.2V. With its
high frequency, synchronous buck-boost internal power
switches, low quiescent current, 1MHz switching fre-
quency and thermally enhanced package, the LTC3441 is
a very versatile and powerful IC for driving Luxeon III
LEDs that require both step-up and step-down capability
from lithium-ion supplies used in very compact hand-
held solutions.
The LTC3441 1MHz switching frequency allows all of the
components to be small, surface mount devices. The
current-mode control topology creates fast transient
response and good loop stability with a minimum num-
ber of external components. The LED pushbutton is
used to manually turn on the LED. The SHDN terminal
can be used to program pulses of light from an external
source for certain flash applications. The DIM terminal
can be used to program the LED for dimmer operation
than 1A LED current using a external PWM signal. The
optional MODE/SYNC terminal can be used to synchro-
nize the LTC3441 clock with an external clock.
The LTC2050 is used to control a constant LED current
at the output with the minimum amount of power dissi-
pation in the sense resistor. The five-pin LTC2050IS5 is
used for minimum components and minimum pins, but
the LTC2050IS6 with a shutdown pin can be used for
extremely low quiescent current. [1]
The LTC3441 and LTC2050 datasheets give complete
descriptions of the parts including operation and appli-
cations information. The datasheets must be read in
conjunction with this Quick Start Guide for demonstra-
tion circuit 773. The LTC3441 is assembled in a small
10-pin thermally enhanced package with exposed pad.
Lumileds’ LXHL-PW09 Luxeon III LED emitter has an
exposed pad slug for thermal enhancement. Proper
board layout is essential for maximum thermal perform-
ance. The LXHL-PW09 datasheet is found on Lumileds
website www.lumileds.com.
Design files for this circuit board are available. Call
the LTC factory.
.
Table 1.
Typical Performance Summary (T
A
= 25°C)
PARAMETER CONDITION VALUE
Input Voltage Range 3–4.2V
V
IN
= 3.6V, U2 LTC2050IS6 w/ Shutdown [1] 1.4µA
LED OFF Input Current [1]
V
IN
= 3.6V, U2 LTC2050IS5 w/out Shutdown [1] 1.08mA
V
LED
V
IN
= 3V to 4.2V, LED ON, I
LED
= 1000mA
3.9V
I
LED
V
IN
= 3V to 4.2V, LED ON 1000mA
LED Ripple Current V
IN
= 3.6V, LED ON, I
OUT
= 1000mA 25mA
PK–PK
Switching Frequency V
IN
= 3V to 4.2V, LED ON 1MHz
Efficiency V
IN
= 3.6V, I
LED
= 1000mA, LED ON 84%
LED Brightness V
IN
= 3.6V, I
LED
= 1000mA, LED ON 80LM
NOTE:
[1] Replace LTC2050IS5 with LTC2050IS6 for low quiescent current during LED OFF. Tie SHDN pin of LTC2050IS6 to SHDN pin of
LTC3441. DC773A is stuffed with LTC2050IS5 without a shutdown pin.
