LM3520
Integrated White LED Driver with Organic LED Display
Power Supply
General Description
The LM3520 is a dual step-up DC/DC converter, designed to
drive up to 5 white LEDs with a constant current and to
power an organic LED display with a constant voltage.
A single external resistor is used to set the maximum LED
current. The LED current can be adjusted by applying a
PWM signal to the EN pin. For higher efficiency the LM3520
operates with pulse frequency modulation (PFM) control
scheme when the sub-display is enabled. When Main dis-
play is enabled, the device is operating in PWM mode.
Overvoltage protection circuitry and a 1MHz switching fre-
quency allow for the use of small, low cost external compo-
nents.
Additional features include a low-side NFET switch that can
turn off the LED string with no DC current path to ground.
The LM3520 is available in a small 14-pin thermally-
enchanced LLP package.
Features
n
Integrated OLED and white-LED driver
n
80% efficiency
n
Drives up 5 LEDs at 20mA/3.6V and 4 LEDs at
30mA/3.6V for main-display
n
Up to 20V
@
50mA/3.6V for sub-display
n
True shutdown isolation
n
Small External Components
n
1 MHz Switching Frequency
n
23V OverVoltage Protection
n
Wide Input Voltage Range: 2.7V to 5.5V
n
Cycle-By-Cycle Current Limit
n
PWM Dimming Control
n
Low Profile 14-Pin LLP(3mm x 4mm x 0.8mm)
Applications
n
Flip-phones/Clam-shell Cellular Phones
n
Handheld Devices
n
High-fashion cellular phones
n
White LED Backlighting
n
Digital Cameras
Typical Applications
20128803
Main Display with OLED Sub Display
PRELIMINARY
February 2005
LM3520
Integrated
White
LED
Driver
with
Organic
LED
Display
Power
Supply
2005 National Semiconductor Corporation
DS201288
www.national.com
Pin Description
Pin #
Pin Name
Description
1
V
SW
Switching Voltage
2
V
IN
Input Voltage
3
AGND
Analog Ground
4
NC
No Connect
5
MAIN_EN
Main Enable
6
SUB_EN
Sub Display Enable
7
PFM_EN
PFM mode: OLED sub-display, pin must be tied to SUB_EN
8
SUB_FB
Sub Display Feedback
9
V
SUB
Sub Display Power Supply Voltage
10
V
O_MAIN
Main Output Voltage
11
MAIN_FB
Main Display Feedback
12
MAIN_RTN
Main Display Return Voltage
13
DGND
Digital Ground
14
NC
No Connect
Ordering Information
Order Number
Package
NSC Package
Marking
Supplied As
LM3520SD
LLP-14
L133B
1000 units, Tape and Reel
LM3520SDX
L133B
4500 units, Tape and Reel
LM3520
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3
Operation Modes
LM3520 has two operating modes; Figure 2 shows main
display in PWM current mode operation, the appropriate
selection of R
FB
resistor in series with four white LEDs set
the output current driving the main display. Figure 3 shows
Sub display in PFM mode, the appropriate selection of
R
SUB1
and R
SUB2
resistors set the output voltage driving the
OLED subdisplay.
20128806
20128807
* Note: The current I
FB1
is very small and is negligible.
20128804
FIGURE 2. Main Display
20128805
FIGURE 3. Sub Display
LM3520
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4
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
V
IN
-0.3V to +7.5V
V
O_MAIN
-0.3V to +25V
V
SW
-0.3V to V
OUT
+0.3V
Main_FB, Main_RTN
-0.3V to +7.5V
MAIN_EN, PFM_EN &
SUB_EN(Note 2)
-0.3V to +7.5V
Continuous Power Dissipation
(Note 3)
Internally Limited
Maximum Junction Temperature
(T
J-MAX
)
+150C
Storage Temperature Range
-65C to +150C
Maximum Lead Temperature
(Soldering, 10 sec)
+265C
ESD Rating (Note 4)
Human Body Model:
Machine Model:
2.0 kV
200V
Operating Ratings
Input Voltage Range
2.7V to 5.5V
Junction Temperature (T
J
) Range
-40C to +125C
Ambient Temperature (T
A
) Range
(Note 3)
-40C to +85C
Thermal Properties
Junction-to-Ambient Thermal Resistance (
JA)
,
55C/W
Leadless Lead frame Package (Note 5)
Electrical Characteristics
(Notes 6, 7) Limits in standard typeface are for T
J
= +25C. Limits in boldface
type apply over the full operating junction temperature range (-40C
= T
J
+125C). Unless otherwise noted: specifications
apply to the LM3520. V
IN
= 3.6V, V(En)
>
1.0V, C
IN
= 10 F (Note 8).
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Enable
Threshold
MAIN_EN = low
SUB_EN = low
0.3
V
MAIN_EN = high
SUB_EN = high
0.95
PFM_EN = low
0.3
V
PFM_EN = high
0.95
I
EN
Enable Pin Current
MAIN_EN = 3.6V (Note 10)
3
5
A
SUB_EN = 3.6V (Note 10)
3
5
PFM_EN = 3.6V
3
5
I
Q
Quiescent Current, Device Not
Switching (PWM mode)
MAIN_FB
>
0.5V
0.5
1.3
mA
Quiescent Current, Device Not
Switching (PFM mode)
SUB_FB
>
1.0V
0.25
0.45
Quiescent Current, Device
Switching
MAIN_FB = 0V or SUB_FB =
0V (open loop)
1.75
4.5
Power Off Current (Shutdown)
MAIN_EN = low
SUB_EN = low
PFM_EN = low
0.1
2
A
V
FB
Feedback Voltage (MAIN_FB)
V
IN
= 3.6V
0.455
0.5
0.545
V
Feedback Voltage (SUB_FB)
V
IN
= 3.6V
1.18
1.23
1.28
I
B
FB Pin Leakage Current
MAIN_FB = 0.5V (Note 9)
10
nA
FB Pin Bias Current
SUB_FB = 1.0V (Note 9)
50
I
Current Limit
Switch Current Limit
V
MAIN_FB
= 0V, V
IN
= 3.6V
0.518
0.7
0.917
A
R
DS
(ON)
Main_Switch R
DS
(ON), N1
I
SW
= 300 mA
0.5
PMOS Switch R
DS
(ON), P1
I
PMOS
= 20 mA
3
MAIN_RTN R
DS
(ON), N2
I
Main_RTN
= 30 mA
3
I
main_RTN_leakage
Main_RTN Leakage Current
V
Main_RTN
= 0.5V, V
IN
= 3.6V
0.2
A
D
Limit
Duty Cycle Limit at PWM & PFM
V
FB
= 0V, V
IN
= 3.6V
90
%
F
SW
Switching Frequency
V
IN
= 3.6V
0.8
1.1
1.4
MHz
I
Leak
Switch Leakage Current
V
SW
= 24V
0.01
0.5
A
LM3520
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