LP3322 Datasheet, PDF (7/8 Pages) Lowpower Semiconductor inc – 1.1MHzFixed-Frequency PWM Operation

Preliminary Datasheet
LP3322
c. Using a Filtered PWM signal
Another common application is using a filtered ^Vin
PWM signal as an adjustable DC voltage for LED
10uH
dimming control. A filtered PWM signal acts as the
Cin
10uF
Cout
1uF
DC voltage to regulate the output current. The
recommended application circuit is shown in the
6 _{Vin OUT} 5
Figure 6. In this circuit, the output ripple depends
on the frequency of PWM signal. For smaller output
voltage ripple (<100mV), the recommended
4 _EN
FB ³
frequency of 2.8V PWM signal should be above
LP3322
2kHz. To fix the frequency of PWM signal and
change the duty cycle of PWM signal can get
R2
different output current. According to the
application circuit of Figure 5, output current is
from 20.5mA to 5.5mA by adjusting the PWM duty
cycle from 10% to 90%.
R3 ^5k
R1
R4
10
PWM
90k
(0-100KHz) ^100K
C2
0.1uF
LP3322 – 00 Vesion 1.0 Datasheet Feb.-2013
www.lowpowersemi.com
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