Page 1
Preliminary Datasheet LP3382
High Performance, Constant Current Switching
Regulator For 8PCS White LED In Series
General Description
The LP3382 is a 1.2MHz PWM boost switching
regulator designed for constant- current white LED
driver applications. The LP3382 can drive a string of
up to 8 white LEDs in series, ensuring uniform
brightness and eliminating several ballast resistors.
The LP3382 implements a constant frequency
1.2MHz PWM control scheme. The high frequency
PWM operation also saves board space by reducing
external component sizes. To improve efficiency, the
feedback voltage is set to 250 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
LP3382
F: Pb-Free
Package:
B6: SOT23-6
Pin Configurations
Features
High Efficiency: 92%
1.2MHzFixed-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
Typical Application Circuit
Vin
PWM
0-200KHz
Cin
10uF
10uH
100k
6
R2
1
LX
Vin
OVP
EN4FB
GND
2
LP3382
SS0520
5
3
Cout
1uF
Marking information
Part Number Top Marking Package
LP3382B6F F5 SOT23-6
Other Information please view website:
www.lowpowersemi.com.
(SOT23-6)
LP3382 – 01 Version 1.0 Datasheet OCT.-2011 www.lowpowersemi.com Page 1 of 9
R1
12
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Functional pin description
SOT-23-6
Pin Name Pin Function
Preliminary Datasheet LP3382
1 SW
2 GND Ground Pin
3 FB
4 EN
5 OVP
6 Vin
Switch Pin. Connect this Pin to inductor and catch diode. Minimize the track
area to reduce EMI.
Feedback Reference Voltage Pin. Series connect a resistor between WLED
and ground as a current sense. Sense the current feedback voltage to set the
current rating.
Chip Enable (Active High). Voltage sensing input to trigger the function of
over voltage protection. Note that this pin is high impedance. There should
be a pull low 100kΩ resistor connected to GND when the control signal is
floating.
Over voltage pin.
Supply Input Voltage Pin. Bypass 1uF capacitor to GND to reduce the input
noise.
Function Block Diagram
LP3382 – 01 Version 1.0 Datasheet OCT.-2011 www.lowpowersemi.com Page 2 of 9
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Typical Application Circuit
Vin
22uH
+
2.2uF
1
Vin
LX
OVP
6
2.2uF
5
Preliminary Datasheet LP3382
Panel
+
Vin
+
2.2uF
22uH
1
Vin
LX
OVP
6
2.2uF
5
Panel
+
GND
2
LP3382
3
EN4FB
LP3382 for 6pcs Application Circuit
Vin
22uH 22uH
+
2.2uF
6
Vin
EN4FB
1
LX
OVP
GND
2
LP3382
2.2uF
5
3
GND
2
LP3382
1
LX
OVP
GND
2
LP3382
3
Rset
5.1
Panel
+
2.2uF
5
3
EN4FB
Rset
12
LP3382 for 2X6pcs Application Circuit
Panel
+
Vin
+
2.2uF
6
Vin
EN4FB
Rset
LP3382 for 7pcs Application Circuit
Vin
22uH
+
6
Vin
EN4FB
1
LX
OVP
GND
2
LP3382
2.2uF
5
3
2.2uF
LP3382 for 27pcs Application Circuit
Rset
12
+
LP3382 for 2X7pcs Application Circuit
Panel
Rset
2
5.1
LP3382 – 01 Version 1.0 Datasheet OCT.-2011 www.lowpowersemi.com Page 3 of 9
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Preliminary Datasheet LP3382
y
Absolute Maximum Ratings
Supply Input Voltage---------------------------------------------------------------------------------------------------−0.3V to 6.0V
SW Input Voltage ---------------------------------------------------------------------------------------------------------−0.3V to 35V
The Other Pins -----------------------------------------------------------------------------------------------------------−0.3V to 5.5V
Power Dissipation, P
Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------------- 280°C
Operation Temperature Range ------------------------------------------------------------------------------ −40°C to 80°C
Storage Temperature Range ----------------------------------------------------------------------------------- −65°C to 150°C
ESD Susceptibility
HBM(Human Body Mode) ---------------------------------------------------------------------------------------- 4KV
MM((Machine Mode)) -------------------------------------------------------------------------------------------- 200V
D @ TA = 25°C SOT-23-6----------------------------------------------------------------------------0.455W
Electrical Characteristics
Parameter
System Supply Input
Operation voltage Range VDD
Under Voltage Lock Out VDD
Supply Current IDD FB=0.2V, Switch
Shut Down Current IDD VEN < 0.4V
Line Regulation
Oscillator
Operation Frequency
Maximum Duty Cycle
Feedback Voltage LP3382
MOSFET
On Resistance of MOSFET RDS(ON)
SW Current Limit ILM
Protection
OVP Threshold VOVP
S
F
OSC
mbol
Test Condition Min Typ. Max Units
VIN : 3.0~4.3V
2.7
93
235 250 265 mV
2.4
90 uA
0.1 1 uA
2
1.2
0.3
2
29
6 V
V
%
MHz
%
Ω
A
V
OVP Sink Current
Shut Down Voltage VEN
Enable on Voltage VEN
Minimum EN Dimming
Threshold
Minimum EN Dimming
Threshold
PWM EN Dimming range
VFB=0 V
VFB=250Mv
0.4
100
0.7
0.7
1.4
200K
5
V
μA
V
V
V
Hz
LP3382 – 01 Version 1.0 Datasheet OCT.-2011 www.lowpowersemi.com Page 4 of 9
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Preliminary Datasheet LP3382
Typical Operating Characteristics
LP3382 – 01 Version 1.0 Datasheet OCT.-2011 www.lowpowersemi.com Page 5 of 9
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Applications Information
Preliminary Datasheet LP3382
LED Current Control
The LP3382 regulates the LED current by setting
the current sense resistor (R1) connecting to
feedback and ground. The internal feedback
reference voltage is 250mV. The LED current can
be set from following equation easily.
ILED=250mV/R1
In order to have an accurate LED current, precision
resistors are preferred (1% is recommended). The
table for R1 selection is shown below.
Power Sequence
In order to assure the normal soft start function for
suppressing the inrush current the input voltage
should be ready before EN pulls high.
Soft-Start
The function of soft-start is made for suppressing
the inrush current to an acceptable value at the
beginning of power-on. The LP3382 provides a
built-in soft-start function by clamping the output
voltage of error amplifier so that the duty cycle of
the PWM will be increased gradually in the
soft-start period.
Current Limiting
The current flow through inductor as charging
period is detected by a current sensing circuit. As
the value comes across the current limiting
threshold, the N-MOSFET will be turned off so that
the inductor will be forced to leave charging stage
and enter discharging stage. Therefore, the inductor
current will not increase over the current limiting
threshold.
OVP/UVLO/OTP
The Over Voltage Protection is detected by a
junction breakdown detecting circuit. Once VOUT
goes over the detecting voltage, LX pin stops
switching and the power N-MOSFET will be turned
off. Then, the VOUT will be clamped to be near
VOVP. As the output voltage is higher than a
specified value or input voltage is lower than a
specified value, the chip will enter protection mode
to prevent abnormal function. As the die
temperature is higher then 160℃, the chip also will
enter protection mode. The power MOSFET will be
turned off during protection mode to prevent
abnormal operation.
Inductor Selection
The recommended value of inductor for 2 to
8WLEDs applications are 4.7 to 22µH. Small size
and better efficiency are the major concerns for
portable device, such as LP3382 used for mobile
phone. The inductor should have low core loss at
1.3MHz and low DCR for better efficiency. To
avoid inductor saturation current rating should be
considered.
Capacitor Selection
Input ceramic capacitor of 2.2uF and output ceramic
capacitor of 1uF are recommended for the LP3382
applications for driving 8 series WLEDs. For better
voltage filtering, ceramic capacitors with low ESR
are recommended. X5R and X7R types are suitable
because of their wider voltage and temperature
ranges.
Dimming control
a. Using a PWM Signal to EN Pin
For controlling the LED brightness, the LP3382 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 200KHz
can insignificantly reduce audio noise when
dimming. The average LED current is proportional
to the PWM signal duty cycle. The magnitude of the
LP3382 – 01 Version 1.0 Datasheet OCT.-2011 www.lowpowersemi.com Page 6 of 9
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Preliminary Datasheet LP3382
PWM signal should be higher than the maximum
enable voltage of EN pin, in order to let the
dimming control perform correctly.
Vin
Cin
10uF
PWM
0-200KHz
10uH
100k
6
R2
1
LX
Vin
OVP
EN4FB
GND
2
LP3382
SS0520
5
3
Cout
1uF
R1
12
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
Cin
10uF
ON/ OFF
10uH
R4
100k
6
1
LX
Vin
OVP
EN4FB
GND
2
LP3382
VDC
SS0520
5
3
R3
56K
Cout
1uF
R2
VFB=250mV
6.8K
R1
12
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%.
Vin
Cin
10uF
ON/ OFF
10uH
6
R4
100k
PWM
(0-100KHz)
1
LX
Vin
OVP
EN4FB
GND
2
LP3382
R69
100K
SS0520
5
3
VFB=250mV
R3
C3
0.1uF
56K
Cout
1uF
R2
6.8K
R1
10
LP3382 – 01 Version 1.0 Datasheet OCT.-2011 www.lowpowersemi.com Page 7 of 9
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Preliminary Datasheet LP3382
Layout Consideration
For best performance of the LP3382, the following
guidelines must be strictly followed.
※ Input and Output capacitors should be placed
close to the IC and connected to ground plane to
reduce noise coupling.
※ The GND and Exposed Pad should be connected
to a strong ground plane for heat sinking and
noise protection.
※ Keep the main current traces as possible as short
and wide.
※ LX node of DC-DC converter is with high
frequency voltage swing. It should be kept at a
small area.
※ Place the feedback components as close as
possible to the IC and keep away from the noisy
devices.
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Packing information
Preliminary Datasheet LP3382
LP3382 – 01 Version 1.0 Datasheet OCT.-2011 www.lowpowersemi.com Page 9 of 9
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