POWER LP3382B6F 1.2mhzfixed-frequency pwm operation Datasheet

Preliminary Datasheet
LP3382S
High Performance, Constant Current Switching
Regulator For 8PCS White LED In Series
General Description
Features
The LP3382S is a 1.2MHz PWM boost switching
regulator designed for constant- current white LED
driver applications. The LP3382S can drive a string
of up to 8 white LEDs in series, ensuring uniform
brightness and eliminating several ballast resistors.
The LP3382S 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.
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
Ordering Information
Vin
4.7uH
Panel
1
4
EN
OVP
FB
5
3
2
Package:
B6: SOT23-6
Vin
LX
6
F: Pb-Free
Cout
2.2uF
GND
Cin
10uF
LP3382S
LP3382S
Pin Configurations
Rset
2
Marking information
Part Number
LP3382SB6F
Top Marking
F5
Package
SOT23-6
Other Information please view website:
www.lowpowersemi.com.
(SOT23-6)
LP3382S – 00 Version 1.0
Datasheet
OCT.-2012
www.lowpowersemi.com
Page 1 of 9
Preliminary Datasheet
LP3382S
Functional pin description
SOT-23-6
Pin Name
Pin Function
1
SW
Switch Pin. Connect this Pin to inductor and catch diode. Minimize the track
area to reduce EMI.
2
GND
Ground Pin
FB
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.
4
EN
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.
5
OVP
Over voltage pin.
6
Vin
Supply Input Voltage Pin. Bypass 1uF capacitor to GND to reduce the input
noise.
3
Function Block Diagram
LP3382S – 00 Version 1.0
Datasheet
OCT.-2012
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Page 2 of 9
Preliminary Datasheet
LP3382S
Typical Application Circuit
Vin
Vin
Panel
Panel
LX
6
4
1
4
3
FB
Vin
5
OVP
EN
3
FB
2
EN
6
5
OVP
GND
Vin
Cout
2.2uF
LX
Cout
2.2uF
1
Cin
2.2uF
4.7uH
Cin
2.2uF
GND
4.7uH
2
LP3382S
LP3382S
4.7uH
Cout
2.2uF
FB
4.7uH
Cout
2.2uF
5
6
3
4
Vin
EN
OVP
FB
5
3
2
EN
OVP
Cin
2.2uF
Panel
2
4
Vin
GND
6
LX
1
Cin
2.2uF
Vin
1
Panel
LP3382S for 2X6pcs Application Circuit
LX
Vin
Rset
5.1
GND
LP3382S for 6pcs Application Circuit
Rset
12
LP3382S
LP3382S
LP3382S for 7pcs Application Circuit
Rset
12
Rset
5.1
LP3382S for 2X7pcs Application Circuit
Vin
4.7uH
Panel
6
EN
OVP
FB
5
3
2
4
Vin
LX
1
Cout
2.2uF
GND
Cin
10uF
LP3382S
Rset
2
LP3382S – 00 Version 1.0
Datasheet
OCT.-2012
www.lowpowersemi.com
Page 3 of 9
Preliminary Datasheet
LP3382S
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, PD @ TA = 25°C SOT-23-6----------------------------------------------------------------------------0.455W
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) ---------------------------------------------------------------------------------------MM((Machine Mode)) --------------------------------------------------------------------------------------------
4KV
200V
Electrical Characteristics
Parameter
Symbol
Test Condition
Min
Typ.
Max
Units
6
V
System Supply Input
Operation voltage Range
VDD
Under Voltage Lock Out
VDD
Supply Current
IDD
Shut Down Current
IDD
2.7
Line Regulation
2.4
V
FB=0.2V, Switch
90
uA
VEN < 0.4V
0.1
VIN : 3.0~4.3V
1
uA
2
%
1.2
MHz
Oscillator
Operation Frequency
FOSC
Maximum Duty Cycle
93
Feedback Voltage
%
LP3382S
250
mV
On Resistance of MOSFET
RDS(ON)
0.3
Ω
SW Current Limit
ILM
2
A
VOVP
29
V
5
μA
MOSFET
Protection
OVP Threshold
OVP Sink Current
Shut Down Voltage
VEN
Enable on Voltage
VEN
Minimum EN Dimming
Threshold
Minimum EN Dimming
Threshold
0.4
0.7
0.7
V
VFB=250Mv
1.4
V
100
Datasheet
V
VFB=0 V
PWM EN Dimming range
LP3382S – 00 Version 1.0
V
OCT.-2012
www.lowpowersemi.com
200K
Hz
Page 4 of 9
Preliminary Datasheet
LP3382S
Typical Operating Characteristics
LP3382S – 00 Version 1.0
Datasheet
OCT.-2012
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Page 5 of 9
Preliminary Datasheet
LP3382S
Applications Information
LED Current Control
The LP3382S 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.
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 2.2 to 22µH. Small size
and better efficiency are the major concerns for
portable device, such as LP3382S 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.
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.
Capacitor Selection
Input ceramic capacitor of 2.2uF and output ceramic
capacitor of 1uF are recommended for the LP3382S
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.
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 LP3382S 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.
Dimming control
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
a. Using a PWM Signal to EN Pin
For controlling the LED brightness, the LP3382S
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
LP3382S – 00 Version 1.0
Datasheet
OCT.-2012
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Page 6 of 9
Preliminary Datasheet
magnitude of the
LP3382S
selection of resistors in Figure 4 sets dimming
control of LED current from 20mA to 0mA.
Vin
4.7uH
SS0520
Cout
1uF
1
Cin
10uF
6
Vin
LX
PWM signal should be higher than the maximum
enable voltage of EN pin, in order to let the
dimming control perform correctly.
OVP
5
4
R2
100k
EN
OVP
FB
ON/OFF
EN
R4
100k
FB
3
2
Cout
1uF
LP3382S
5
R3
3
VFB=300mV
Vin
LX
1
SS14
GND
6
PWM
4
4.7uH
R2
56K
VDC
6.8K
R1
12
2
Cin
10uF
GND
Vin
LP3382S
0-1MHz
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
4.7uH
LP3382S – 00 Version 1.0
Datasheet
OCT.-2012
Cout
1uF
ON/OFF
R4
100k
EN
LX
OVP
FB
5
3
LP3382S
R69
PWM
(0-100KHz) 100K
www.lowpowersemi.com
VFB=300mV
4
Vin
GND
6
2
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
SS0520
1
Cin
10uF
R2
R3
6.8K
56K
C3
0.1uF
Page 7 of 9
R1
15
Preliminary Datasheet
LP3382S
Layout Consideration
For best performance of the LP3382S, 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.
LP3382S – 00 Version 1.0
Datasheet
OCT.-2012
www.lowpowersemi.com
Page 8 of 9
Preliminary Datasheet
LP3382S
Packing information
LP3382S – 00 Version 1.0
Datasheet
OCT.-2012
www.lowpowersemi.com
Page 9 of 9
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