Preliminary
RT9272
SP Voltage vs. Input Voltage
Dimming Control for 4LEDs
1.4
1.2
1
18
16
14
12
10
8
VIN = 3.7V, ILED = 20mA
VIH
VIL
0.8
0.6
0.4
0.2
0
6
100kHz
200Hz
500Hz
1kHz
4
2
0
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5
Input Voltage (V)
20
30
40
50
60
70
80
Duty (%)
Dimming Control for 2LEDs
Dimming Control for 3LEDs
20
18
16
14
12
10
8
VIN = 3.7V, ILED = 20mA
VIN = 3.7V, ILED = 20mA
18
16
14
12
10
8
1kHz
1kHz
500Hz
200Hz
100Hz
500Hz
200Hz
100Hz
6
6
4
4
2
2
0
0
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Duty (%)
Duty (%)
Dimming Operation for 3LEDs
Dimming Operation for 3LEDs
EN (2V/Div)
EN (2V/Div)
VOUT (5V/Div)
VOUT (5V/Div)
ILED (10mA/Div)
ILED (10mA/Div)
VIN = 3.7V, f = 1kHz, Duty = 50%
VIN = 3.7V, f = 100Hz, Duty = 50%
Time (4ms/Div)
Time (400μs/Div)
DS9272-09 August 2007
www.richtek.com
7
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
