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PDF LP3311S Data sheet ( Hoja de datos )
| Número de pieza | LP3311S | |
| Descripción | Constant Current Switching Regulator | |
| Fabricantes | Lowpowersemi | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LP3311S (archivo pdf) en la parte inferior de esta página. Total 7 Páginas | ||
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Preliminary Datasheet
LP3311S
High Performance, Constant Current Switching
Regulator For 8PCS White LED In Series
General Description
The LP3311S is a 1MHz PWM boost switching regulator
designed for constant current white LED driver applications.
The LP3311S can drive a string of up to 8 white LED in
series, ensuring uniform brightness and eliminating several
ballast resistors. The LP3311S implements a constant
frequency 1MHz PWM control scheme. The high frequency
PWM operation also saves board space by reducing
external component size. To improve efficiency, the
feedback voltage is set to 200 mV, which reduces the
power dissipation in the current setting resistor. Highly
integration and internal compensation network minimizes
as 5 external component counts. Optimized operation
frequency can meet the requirement of small LC filters
value and low operation current with high efficiency.
Ordering Information
LP3311S
Features
High Efficiency: 90%
1MHz Fixed-Frequency PWM Operation
Maximum Output Voltage up to 29V
Operating Range : 2.7V to 5.5V
Shutdown Supply Current:<1uA
Available in SOT23-6 Package
Built-in 29V Over Voltage Protection
Minimize the External Component
RoHS Compliant and 100% Lead (Pb)-Free
Applications
WLED Backlight driver
OLED Backlight driver
PDA
MID/PTV
F: Pb-Free
Package:
B6: SOT23-6
Pin Configurations
IN
OVP
EN
Typical Application Circuit
Vin
10uF
4. 7uH
Vin SW
EN OVP
1uF
65
4
GND
FB
LP3311S
R1
1 23
SW
GND
SOT- 23- 6
FB
LP3311s – 02 Version 2.0 Datasheet May.-2013
www.lowpowersemi.com
Page 1 of 7
1 page  
Preliminary Datasheet
LP3311S
Applications Information
LED Current Control
The LP3311S regulates the LED current by setting the
current sense resistor (R1) connecting to feedback
and ground. The internal feedback reference voltage is
200mV. The LED current can be set from following
equation easily.
ILED=200mV/R1
In order to have an accurate LED current, precision
resistors are preferred (1% is recommended). The
table for R1 selection is shown below.
Inductor Selection
The recommended value of inductor for 2 to 10
WLEDs applications are 4.7 to 22µH. Small size and
better efficiency are the major concerns for portable
device, such as LP3311S used for mobile phone. The
inductor should have low core loss at 1MHz and low
DCR for better efficiency. To avoid inductor saturation
current rating should be considered.
Dimming control
a. Using a PWM Signal to EN Pin
For controlling the LED brightness, the LP3311S can
perform the dimming control by applying a PWM signal
to EN pin. The internal soft-start and wide range
dimming frequency from 100Hz to 1MHz can
insignificantly reduce audio noise when dimming. The
average LED current is proportional to the PWM signal
duty cycle. The magnitude of the PWM signal should
be higher than the maximum enable voltage of EN pin,
in order to let the dimming control perform correctly.
Vin
10uF
PWM
4.7uH
Vin SW
EN OVP
GND
FB
LP3311S
1uF
10R
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.
Vin
10uF
4.7uH
Vin SW
1uF
EN OVP
GND
FB
LP3311S
VDC
5K
65K
10R
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
LP3311s – 02 Version 2.0 Datasheet May.-2013
www.lowpowersemi.com
Page 5 of 7
5 Page | ||
| Páginas | Total 7 Páginas | |
| PDF Descargar | [ Datasheet LP3311S.PDF ] | |
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