
White LED Step-Up Converter in SOT23
Typical Operating Characteristics
(See Typical Application Circuit , V+ = 3V, I LED = 15mA, L = 33μH, C OUT = 1μF, C COMP = 0.15μF, R SENSE = 5 Ω , CTRL = 1V, 2 LEDs,
T A = +25 ° C, unless otherwise noted.)
SWITCHING FREQUENCY
90
EFFICIENCY vs. SUPPLY VOLTAGE
I OUT = 15mA
90
EFFICIENCY vs. LOAD CURRENT
2 LEDs
1.4
vs. SUPPLY VOLTAGE
T A = +85 ° C
88
86
2 LEDs
85
3 LEDs
1.3
T A = +25 ° C
80
84
1.2
T A = -40 ° C
82
3 LEDs
75
80
70
1.1
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0
10
20
30
40
50
60
2.5
3.0
3.5
4.0 4.5
5.0
5.5
SUPPLY VOLTAGE (V)
POWER-UP WAVEFORMS
MAX1848 toc04
1V
LOAD CURRENT (mA)
POWER-UP WAVEFORMS
MAX1848 toc05
1V
SUPPLY VOLTAGE (V)
SHUTDOWN WAVEFORMS
MAX1848 toc06
1V
V CTRL
I IN
0
38mA
V CTRL
I IN
0
38mA
0
V CTRL
I IN
0
38mA
0
0
I LED
t RISE = 15ms
C COMP = 0.15μF
15mA
0
I LED
t RISE = 110ms
C COMP = 1 μ F
15mA
0
I LED
15mA
0
50ms/div
SHUTDOWN WAVEFORMS
MAX1848 toc07
50ms/div
LINE-TRANSIENT RESPONSE
MAX1848 toc08
20 μ s/div
V CTRL TRANSIENT RESPONSE
MAX1848 toc09
V CTRL
1V
0
V IN
3.50V
3.00V
V CTRL
2.0V
1.0V
V OUT
6.25V
V OUT
V OUT EVENTUALLY
DECAYS TO V+ = 3V
6.3V
4.9V
500mV/div
V OUT
C COMP = 0.15μF
6.7V
6.3V
30mA
V COMP
1.5V
0
I LED
C COMP = 0.15μF
15mA
10mA/div
I LED
15mA
2 μ s/div
5ms/div
20ms/div
4
_______________________________________________________________________________________