LP3321 Datasheet, PDF (7/9 Pages) Lowpower Semiconductor inc – 1.3MHzFixed-Frequency PWM Operation

Preliminary Datasheet
LP3321
c. Using a Filtered PWM signal
Another common application is using a filtered ^Vin
PWM signal as an adjustable DC voltage for LED
dimming control. A filtered PWM signal acts as the
Cin
10uF
10uH
D1
SS14
Cout
1uF
DC voltage to regulate the output current. The
recommended application circuit is shown in the
5 _Vin
Figure 6. In this circuit, the output ripple depends
LP3321
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
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
Cout
0.1uF
LP3321 – 01 Vesion 1.1 Datasheet Feb.-2011
www.lowpowersemi.com
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