SC600
POWER MANAGEMENT
Applications Information (Cont.)
Brightness Control with PWM Input
current, and then changes to 32kHz when there is no load
current. This is done to save battery power by taking ad-
Brightness control using a PWM input can be achieved vantage of the lower 280μA quiescent current at 32kHz.
with the application circuit below. Note that by connecting The ripple voltage seen at the output is reasonable for
CX8 to the PWM signal the switching frequency is changed LED applications, but the output capacitance can be in-
as the PWM signal changes. The charge pump operates creased to reduce the ripple if required. The sum of the
at 262kHz during the on-time when there is a demand for LED currents for this circuit is 55mA during the on-time.
White LED Driver Circuit with PWM Brightness Control
U1
5.0V
1
2
3
6
4
5
2.7V to 6.5V
VIN
EN
VOUT
CF1+
Cin
1uF
Cout
1uF
Cbucket1
1uF
9
CF1-
CF2+
CF2-
100
100
100
CD4
CX8
10
7
Cbucket2
1uF
GND
8
PW M
Voltage Waveforms for LED Driver Circuit
Battery Current vs. Input Voltage
for Various Duty Cycles
Ripple Voltage vs. Input Voltage
500
450
400
350
300
250
200
150
100
50
89.20%
70.30%
50.20%
30.20%
Vout p-p
Vin p-p
120
100
80
60
40
20
0
0
2.8
3
3.2
3.4
3.6
3.8
4
2.8
3.3
3.8
4.3
4.8
5.3
5.8
Input Voltage [V]
Input Voltage [V]
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9
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