Preliminary Datasheet LP3322 High Performance, Constant Current

Preliminary Datasheet
LP3322
High Performance, Constant Current Switching
Regulator For 10PCS White LED In Series
General Description
Features
The LP3322 is a 1.1MHz PWM boost switching
regulator designed for constant- current white LED
driver applications. The LP3322 can drive a string of
up to 10 white LEDs in series or 3s9p LEDs from
3.6V, ensuring uniform brightness and eliminating
several ballast resistors. The LP3322 implements a
constant frequency 1.1MHz 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
200mV and 300mV, 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
High Efficiency: 88% 1.1MHzFixed-Frequency PWM Operation
Maximum Output Voltage up to 36V
Operating Range : 2.7V to 5.5V
Shutdown Supply Current:<1uA Available in SOT23-6 Package Built-in 39V 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
10uH
SD103
6
LX
LP3322
1
Cin
10uF
Vin
OUT
Cout
1uF
5
4
FB
3
2
Package:
B6: SOT23-6
EN
GND
F: Pb-Free
LP3322
FB Voltage
Default: VFB=200mV
A: VFB=300mV
VFB=200mV
R1
10
Pin Configurations
Marking information
Please view website.
(SOT23-6)
LP3322 – 00 Vesion 1.0 Datasheet
Feb.-2013
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Page 1 of 8
Preliminary Datasheet
LP3322
Functional pin description
SOT-23-6
Pin Name
Pin Function
1
LX
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
OUT
Over Voltage protection pin.
6
Vin
Supply Input Voltage Pin. Bypass 1uF capacitor to GND to reduce the input
noise.
3
Function Block Diagram
LP3322 – 00 Vesion 1.0 Datasheet
Feb.-2013
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Page 2 of 8
Preliminary Datasheet
LP3322
Absolute Maximum Ratings
Supply Input Voltage---------------------------------------------------------------------------------------------------−0.3V to 6.0V
SW Input Voltage --------------------------------------------------------------------------------------------------------−0.3V to 43V
The Other Pins ----------------------------------------------------------------------------------------------------------−0.3V to 5.5V
Power Dissipation, PD @ TA = 25°C TSOT-23-5/6-----------------------------------------------------------------------0.455W
Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------- 260°C
Operation Temperature Range ---------------------------------------------------------------------------------−40°C to 80°C
Storage Temperature Range ----------------------------------------------------------------------------------------−65°C to 150°C
Electrical Characteristics
Parameter
Symbol
Test Condition
Min
Typ.
Max
Units
6
V
System Supply Input
Operation voltage Range
VDD
2.7
Under Voltage Lock Out
VDD
2.2
Supply Current
IDD
FB=0.2V, Switch
430
550
uA
Shut Down Current
IDD
VEN < 0.4V
0.1
1
uA
Line Regulation
VIN : 3.0~4.3V
2.4
2.6
2
V
%
Oscillator
Operation Frequency
0.9
FOSC
Maximum Duty Cycle
Feedback Voltage
1.1
1.3
93
MHz
%
LP3322
190
200
210
mV
LP3322A
285
300
315
mV
MOSFET
On Resistance of MOSFET
RDS(ON)
0.5
Ω
SW Current Limit
ILM
1.4
A
VOVP
39
V
5
μA
Protection
OVP Threshold
OVP Sink Current
Shut Down Voltage
VEN
Enable on Voltage
VEN
Minimum EN Dimming
Threshold
Minimum EN Dimming
Threshold
LP3322 – 00 Vesion 1.0 Datasheet
V
0.4
0.6
V
VFB=0 V
0.7
V
VFB=200mV
1.4
V
Feb.-2013
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Page 3 of 8
Preliminary Datasheet
LP3322
Typical Operating Characteristics
LP3322 – 00 Vesion 1.0 Datasheet
Feb.-2013
www.lowpowersemi.com
Page 4 of 8
Preliminary Datasheet
LP3322 – 00 Vesion 1.0 Datasheet
Feb.-2013
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LP3322
Page 5 of 8
Preliminary Datasheet
LP3322
Applications Information
Vin
10uH
4
LX
6
PWM
Cout
1uF
1
Cin
10uF
Vin
EN
FB
5
3
2
ILED=200mV/R1 (LP3322)
ILED=300mV/R1 (LP3322A)
OUT
GND
LED Current Control
The LP3322 regulates the LED current by setting
the current sense resistor (R1) connecting to
feedback and ground. The internal feedback
reference voltage is 200mV or LP3322A is 300mV.
The LED current can be set from following equation
easily.
LP3322
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 10µH. Small size
and better efficiency are the major concerns for
portable device, such as LP3322 used for mobile
phone. The inductor should have low core loss at
1.1MHz and low DCR for better efficiency. To
avoid inductor saturation current rating should be
considered.
Dimming control
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
Feb.-2013
10uH
Cout
1uF
EN
OUT
FB
5
3
LP3322
R3
VDC
www.lowpowersemi.com
90k
VFB=200mV
4
Vin
GND
6
LX
1
Cin
10uF
2
a. Using a PWM Signal to EN Pin
For controlling the LED brightness, the LP3322 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.
LP3322 – 00 Vesion 1.0 Datasheet
R1
10
R2
5k
R1
10
Page 6 of 8
Preliminary Datasheet
LP3322 – 00 Vesion 1.0 Datasheet
Feb.-2013
Vin
10uH
Cout
1uF
4
Vin
EN
OUT
GND
6
LX
1
Cin
10uF
FB
5
3
2
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 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%.
LP3322
LP3322
R2
R3
R4
PWM
(0-100KHz) 100K
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5k
R1
10
90k
C2
0.1uF
Page 7 of 8
Preliminary Datasheet
LP3322
Packing information
LP3322 – 00 Vesion 1.0 Datasheet
Feb.-2013
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Page 8 of 8