MP1521
High Efficiency
White LED Driver
Monolithic Power Systems
Application Circuits Continued
Figure 5: Two Strings of Four (4) LEDs or Eight (8) LEDs Total
L1
47µH
V
IN
IN
C
IN
4.7µF
Efficiency vs LED current using
47µH Toko D62CB Inductor
Efficiency (%)
90
80
V
IN
= 5V
70
60
50
V
IN
= 4V
V
IN
= 3V
D1, B130
1
SW
10
ON
OFF
MP1521
EN
2
C
OUT
1uF
GND
9
White LEDs
GND
EN
3
REF
OLS
8
BRT
4
BRT
FB1
5
7
15
25
35
45
Total LED Current (mA)
5
FB3
FB2
6
LED current (mA)
20
25
20
15
10
2.5
Line Regulation using
47µH Toko D62CB
Inductor
20
3
3.5
V
IN
(V)
4
4.5
Figure 6: Three Strings of Three (3) LEDs or Nine (9) LEDs Total
L1
47µH
V
IN
D1, B130
1
Efficiency vs LED current using
47µH Toko D62CB Inductor
100
Efficiency (%)
90
80
70
60
50
V
IN
= 5V
V
IN
= 4V
V
IN
= 3V
IN
SW
10
C
IN
4.7µF
ON
MP1521
EN
2
C
OUT
1µF
GND
9
GND
OFF
EN
White LEDs
3
REF
OLS
8
BRT
4
BRT
FB1
7
0
20
40
60
80
LED current (mA)
5
FB3
FB2
6
LED Current (mA)
22
20
18
16
1.4
Line regulation using
47µH Toko D62CB Inductor
20
20
20
2.0
2.
6
3.0
V
IN
(V)
3.6
4.2
MP1521 Rev 2.7 10/06/04
www.monolithicpower.com
7
MPS [ MONOLITHIC POWER SYSTEMS ]
