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LP3382 Datasheet(PDF) 7 Page - Lowpower Semiconductor inc

Part No. LP3382
Description  1.2MHzFixed-Frequency PWM Operation
Download  9 Pages
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Manufacturer  POWER [Lowpower Semiconductor inc]
Direct Link  http://www.lowpowersemi.com
Logo POWER - Lowpower Semiconductor inc

LP3382 Datasheet(HTML) 7 Page - Lowpower Semiconductor inc

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Preliminary Datasheet
LP3382
LP3382 – 01 Version 1.0 Datasheet
OCT.-2011
www.lowpowersemi.com
Page 7 of 9
PWM signal should be higher than the maximum
enable voltage of EN pin, in order to let the
dimming control perform correctly.
Cout
1uF
Cin
10uF
10uH
R1
12
Vin
R2
100k
SS0520
PWM
EN
4
FB
3
Vin
6
OVP
5
LP3382
0-200KHz
b. Using a DC Voltage
Using a variable DC voltage to adjust the brightness
is a popular method in some applications. The
dimming control using a DC voltage circuit is
shown in Figure 4. According to the Superposition
Theorem, as the DC voltage increases, the voltage
contributed to VFB increases and the voltage drop
on R2 decreases, i.e. the LED current decreases. For
example, if the VDC range is from 0V to 2.8V, the
selection of resistors in Figure 4 sets dimming
control of LED current from 20mA to 0mA.
Cout
1uF
10uH
Cin
10uF
R1
12
Vin
R3
56K
R2
6.8K
VDC
SS0520
R4
100k
ON/OFF
EN
4
FB
3
Vin
6
OVP
5
LP3382
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
recomended 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
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%.
Cout
1uF
10uH
Cin
10uF
Vin
R4
100k
SS0520
ON/OFF
EN
4
FB
3
Vin
6
OVP
5
LP3382
PWM
R2
6.8K
R1
10
R3
56K
R69
100K
C3
0.1uF
(0-100KHz)


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