Datasheet

LT3477
12
3477fc
APPLICATIONS INFORMATION
Figure 7c. Effi ciency and LED Current
vs PWM Duty Cycle
Figure 7b. PWM Dimming Waveforms
10μs/DIV
I
LED
200mA/DIV
I
L
1A/DIV
PWM
5V/DIV
3477 F07b
V
IN
= 5V
4 LEDs
300mA
PWM FREQ = 100Hz
BOOST
PWM DUTY CYCLE (%)
0
75
80
85
80
3477 F07c
70
65
20 40 60 100
60
55
50
250
300
350
200
150
100
50
0
EFFICIENCY (%)
V
IN
= 5V
BOOST
4 LEDs, 300mA
PWM FREQUENCY = 100Hz
EFFICIENCY
LED CURRENT
I
SN1
I
SP1
V
IN
I
ADJ2
I
ADJ1
FBN
I
SP2
FBP
V
REF
1M
C2
10μF
C1
3.3μF
V
IN
5V
C1: TAIYO YUDEN EMK316BJ335ML
C2: TAIYO YUDEN UDK325BJ106MM
L1: TOKO D53LC (PN# A915AY-2ROM)
D1: ZETEX ZLLS1000
D2: DIODES INC 1N4148
NMOS1: ZETEX 2N7002
NMOS2: FAIRCHILD FDG327N
LED1 TO LED4: LUMILEDS LXHL-BW02
C
C
10nF
C
SS
33nF
300mA
LED1
LED2
LED3
LED4
3477 F07a
75k
6.81k
NMOS1
NMOS2
OUT
100k
0
5V
100Hz
PWM
R
C
2.4k
R
SENSE
0.33Ω
SW
L1
2.0μH
D1
D2
SS
GND
LT 3 4 7 7
I
SN2
R
T
SHDN
V
C
Figure 7a. 5V to 4 White LEDs: Boost With PWM Dimming