LP3321 datasheet(7/9 Pages) POWER

7 / 9 page

Preliminary Datasheet

LP3321

LP3321 – 01 Vesion 1.1 Datasheet

Feb.-2011

www.lowpowersemi.com

Page 7 of 9

c. Using a Filtered PWM signal

Another common application is using a filtered

PWM signal as an adjustable DC voltage for LED

dimming control. A filtered PWM signal acts as the

DC voltage to regulate the output current. The

recommended application circuit is shown in the

Figure 6. In this circuit, the output ripple depends

on the frequency of PWM signal. For smaller output

voltage

ripple

(<100mV),

the

recommended

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

different

output

current.

According

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%.

Cin

10uF

SS14

(0-100KHz)

PWM

10uH

Vin

Cout

1uF

LP3321

Vin

Cout

0.1uF

90k

100K

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