Datasheet

LT3478/LT3478-1
19
34781f
TYPICAL APPLICATIO S
U
15W, 6 LEDs at 700mA, Boost LED Driver
LT3478-1
SHDN
V
REF
OUT
LED
CTRL2
OVPSET
CTRL1
PWM SS V
C
R
T
V
IN
V
S
LSW
C2
10µF
25V
R1
45.3k
R4
54.9k
R
T
69.8k
f
OSC
= 500kHz
100Hz
R2
130k
PWM
DIMMING RATIO = 1000:1
L1: CDRH104R-100NC
D1: PDS560
Q1: Si2318DS
LEDs: LUXEON III (WHITE)
700mA
D1
3478 TA02a
L1
10µH
3.3V
0V
V
IN
8V TO 16V
C1
4.7µF
25V
C
C
0.1µF
C
SS
1µF
R3
10k
Q1
PWM DIMMING RATIO = 1000:1
(SEE EFFICIENCY ON PAGE 1)
PWM
5V/DIV
INDUCTOR
CURRENT
1A/DIV
I
LED
0.5A/DIV
3478 TA02b
2µs/DIV
f
PWM
= 100Hz
LT3478-1 PWM Dimming
Waveforms
APPLICATIO S I FOR ATIO
WUU
U
3252 F08
OUTPUT CAPACITOR
C
VS
V
S
C
VIN
V
IN
INDUCTOR
1
2
3
4
5
6
7
8
LT3478/LT3478-1
16
15
14
13
12
11
10
9
EXPOSED PAD
PIN 17
POWER GND
ANALOG GND
V
IN
BYPASS CAP
V
OUT
GND
(CONNECT MULTIPLE GROUND PLANES
THROUGH VIAS UNDERNEATH THE IC)
SOLDER THE EXPOSED PAD (PIN 17)
TO THE ENTIRE COPPER GROUND PLANE
UNDERNEATH THE DEVICE
SW
SW
V
IN
V
S
L
V
OUT
LED
OVPSET
L
SW
SS
R
T
PWM
CTRL2
CTRL1
SHDN
V
REF
V
C
C
SS
C
C
R
T
R
R
C
C
F
C
R
SENSE
(LT3478 ONLY)
R
SCHOTTKY
DIODE
R
R
R
R
Figure 12. Recommended Layout for LT3478/LT3478-1 (Boost Confi guration)