LP3311 Datasheet, PDF (7/8 Pages) Lowpower Semiconductor inc – 1.3MHzFixed-Frequency PWM Operation

Preliminary Datasheet
LP3311
Vin
c. Using a Filtered PWM signal
4.7uH
Another common application is using a filtered
Cin
Cout
10uF
U4
1uF
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
6
5
Vin OVP
recommended application circuit is shown in the
Figure 6. In this circuit, the output ripple depends
4
EN
3
FB
on the frequency of PWM signal. For smaller output
voltage ripple (<100mV), the recommended
LP3311
frequency of 2.8V PWM signal should be above
R2
2kHz. To fix the frequency of PWM signal and
change the duty cycle of PWM signal can get
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
R3 ^5k
R1
R4
PWM
90k
10
(0-100KHz) ^100K
Cout
0.1uF
cycle from 10% to 90%.
For Larger Panel application Circuit
Vin
Cin
10uF
4.7uH
6 _{Vin OVP} 5
Cout
4.7uF
PWM
4 _EN
FB ³
LP3311
3S13P
R1
12
LP3311 – 00 Version 1.0 Datasheet Feb.-2011
www.lowpowersemi.com
Page 7 of 8