NSC LM3520SD Integrated white led driver with organic led display power supply Datasheet

LM3520
Integrated White LED Driver with Organic LED Display
Power Supply
General Description
Features
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.
n Integrated OLED and white-LED driver
n 80% efficiency
n Drives up to 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)
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 display is enabled, the device is operating in PWM mode.
Overvoltage protection circuitry and a 1MHz switching frequency allow for the use of small, low cost external components.
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 thermallyenchanced LLP package.
Applications
n
n
n
n
n
Flip-phones/Clam-shell Cellular Phones
Handheld Devices
High-fashion cellular phones
White LED Backlighting
Digital Cameras
Typical Applications
20128803
Main Display with OLED Sub Display
© 2005 National Semiconductor Corporation
DS201288
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LM3520 Integrated White LED Driver with Organic LED Display Power Supply
September 2005
LM3520
Functional Block Diagram
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FIGURE 1. Functional Block Diagram
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2
LM3520
Pin Descriptions
Pin #
Pin Name
Description
1
VSW
2
VIN
3
AGND
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
VSUB
10
VO_MAIN
11
MAIN_FB
12
MAIN_RTN
13
DGND
14
NC
Switching Voltage
Input Voltage
Analog Ground
Sub Display Power Supply Voltage
Main Output Voltage
Main Display Feedback
Main Display Return Voltage
Digital Ground
No Connect
Ordering Information
Order Number
LM3520SD
LM3520SDX
Package
LLP-14
NSC Package
Marking
Supplied As
L133B
1000 units, Tape and Reel
L133B
4500 units, Tape and Reel
3
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LM3520
the output current driving the main display. Figure 3 shows
Sub display in PFM mode, the appropriate selection of
RSUB1 and RSUB2 resistors set the output voltage driving the
OLED subdisplay.
Operation Modes
LM3520 has two operating modes; Figure 2 shows main
display in PWM current mode operation, the appropriate
selection of RFB resistor in series with four white LEDs set
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FIGURE 2. Main Display
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FIGURE 3. Sub Display
20128807
* Note: The current IFB1 is very small and is negligible.
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ESD Rating (Note 4)
Human Body Model:
Machine Model:
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
VIN
−0.3V to +7.5V
VO_MAIN
−0.3V to +25V
VSW
−0.3V to VOUT
+0.3V
Main_FB, Main_RTN
Operating Ratings
Input Voltage Range
−0.3V to +7.5V
MAIN_EN, PFM_EN &
SUB_EN(Note 2)
−0.3V to +7.5V
Continuous Power Dissipation
(Note 3)
2.0 kV
200V
2.7V to 5.5V
Junction Temperature (TJ) Range
−40˚C to +125˚C
Ambient Temperature (TA) Range
(Note 3)
−40˚C to +85˚C
Thermal Properties
Internally Limited
Junction-to-Ambient Thermal Resistance (θJA),
Maximum Junction Temperature
(TJ-MAX)
55˚C/W
Leadless Lead frame Package (Note 5)
+150˚C
Storage Temperature Range
−65˚C to +150˚C
Maximum Lead Temperature
(Soldering, 10 sec)
+265˚C
Electrical Characteristics (Notes 6, 7) Limits in standard typeface are for TJ = +25˚C. Limits in boldface
type apply over the full operating junction temperature range (−40˚C ≤ = TJ ≤ +125˚C). Unless otherwise noted: specifications
apply to the LM3520. VIN = 3.6V, V(En) > 1.0V, CIN = 10 µF (Note 8).
Symbol
Enable
Threshold
Parameter
Conditions
Min
Typ
MAIN_EN = low
SUB_EN = low
0.3
MAIN_EN = high
SUB_EN = high
PFM_EN = low
IQ
Enable Pin Current
0.3
0.95
MAIN_EN = 3.6V (Note 10)
3
5
SUB_EN = 3.6V (Note 10)
3
5
PFM_EN = 3.6V
3
5
0.5
1.3
0.25
0.45
Quiescent Current, Device Not
Switching (PWM mode)
MAIN_FB > 0.5V
Quiescent Current, Device Not
Switching (PFM mode)
SUB_FB > 1.0V
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
Feedback Voltage (MAIN_FB)
VIN = 3.6V
0.455
0.5
0.545
Feedback Voltage (SUB_FB)
VIN = 3.6V
1.18
1.23
1.28
FB Pin Leakage Current
MAIN_FB = 0.5V (Note 9)
10
FB Pin Bias Current
SUB_FB = 1.0V (Note 9)
50
ICurrent Limit
Switch Current Limit
VMAIN_FB = 0V, VIN = 3.6V
RDS(ON)
Main_Switch RDS(ON), N1
ISW = 300 mA
0.5
PMOS Switch RDS(ON), P1
IPMOS = 20 mA
3
IMain_RTN = 30 mA
3
VFB
IB
MAIN_RTN RDS(ON), N2
Units
V
0.95
PFM_EN = high
IEN
Max
Imain_RTN_leakage Main_RTN Leakage Current
VMain_RTN = 0.5V, VIN = 3.6V
DLimit
Duty Cycle Limit at PWM & PFM
VFB = 0V, VIN = 3.6V
FSW
Switching Frequency
VIN = 3.6V
ILeak
Switch Leakage Current
VSW = 24V
5
0.518
0.7
µA
mA
µA
V
nA
0.917
A
Ω
0.2
90
0.8
V
µA
%
1.1
1.4
MHz
0.01
0.5
µA
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LM3520
Absolute Maximum Ratings (Note 1)
LM3520
Electrical Characteristics (Notes 6, 7) Limits in standard typeface are for TJ = +25˚C. Limits in boldface
type apply over the full operating junction temperature range (−40˚C ≤ = TJ ≤ +125˚C). Unless otherwise noted: specifications
apply to the LM3520. VIN = 3.6V, V(En) > 1.0V, CIN = 10 µF (Note 8). (Continued)
Symbol
OVP
UVP
Min
Typ
Max
Output Over-Voltage Protection
Parameter
ON Threshold
Conditions
22.2
23.2
24.2
(Main & Sub Displays)
OFF Threshold
21.5
22.5
23.5
Input Under-Voltage Protection
ON Threshold
2.3
2.4
2.5
OFF Threshold
2.35
2.45
2.55
IVout_main_leak
VOUT Leakage Current
VOUT = VIN, MAIN_EN =
SUB_EN = 0V
0.1
IVout_main_bias
VOUT Bias Current at No Load
VOUT = 20V, SUB_EN = 0
60
Units
V
V
nA
150
µA
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation of
the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the
Electrical Characteristics tables.
Note 2: Enable signal must not be higher than Input voltage.
Note 3: In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be
derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 125oC), the maximum power
dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the part/package in the application (θJA), as given by the
following equation: TA-MAX = TJ-MAX-OP – (θJA x PD-MAX).
Note 4: The Human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. The machine model is a 200 pF capacitor discharged
directly into each pin. MIL-STD-883 3015.7
Note 5: Junction-to-ambient thermal resistance (θJA) is taken from a thermal modeling result, performed under the conditions and guidelines set forth in the JEDEC
standard JESD51-7. The test board is a 4-layer FR-4 board measuring 101.6mm x 76.2mm x 1.6mm. Thickness of the copper layers are 2oz/1oz/1oz/2oz. The
middle layer of the board is 60mm x 60mm. Ambient temperature in simulation is 22˚C, still air.
Junction-to-ambient thermal resistance is highly application and board-layout dependent. In applications where high maximum power dissipation exists, special care
must be paid to thermal dissipation issues in board design.
Note 6: All voltage is with respect toGND.
Note 7: Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm.
Note 8: CIN and COUT: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics.
Note 9: Feedback current flows out of the Sub_ FB pin.
Note 10: Current flows into the pin.
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Switching Quiescent Current vs. Vin
(Disconnected LEDs from VO_Main & Rsub1 from Vsub)
Close Loop
Non-Switching Quiescent Current vs. Vin
(Disconnected Rfb from LED & Rsub2 from Vsub)
Close Loop
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20128809
Duty Cycle vs. Load Current (PWM at Main_EN)
VIN = 3.6V
Oscillator Frequency vs. Vin
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20128813
Vsub(18V) vs. Load
Vsub (15V) vs. Load
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20128814
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LM3520
Typical Performance Characteristics Typical Application circuit Figure 1, VIN = 3.6V, L = 10µH, D =
CMMSHI-40, CIN = 10µF, COUT = 1µF , TA = 25˚C , Unless otherwise Stated.
LM3520
Typical Performance Characteristics Typical Application circuit Figure 1, VIN = 3.6V, L = 10µH, D =
CMMSHI-40, CIN = 10µF, COUT = 1µF , TA = 25˚C , Unless otherwise Stated. (Continued)
Shutdown Current vs. Vin
Feedback Voltage vs. Vin (4 LEDs)
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20128817
Feedback Voltage vs. Vin (3 LEDs)
Feedback Voltage vs. Vin (2 LEDs)
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20128828
Main Display Efficiency (4 LEDs)
Main Display Efficiency ( 3 LEDs)
20128822
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20128821
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Main Display Efficiency (2 LEDs)
Vsub Efficiency vs. Load (Vsub = 15V)
20128825
20128823
Vsub Efficiency vs. Load (Vsub = 18V)
Vsub Efficiency vs. Load (Vsub = 20V)
20128826
20128824
Typical PWM Switching Waveform
(Vin = 3.6V at 30mA LED Current)
Typical PWM Switching Waveform
(Vin = 3.6V at 4mA LED Current)
20128839
20128837
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LM3520
Typical Performance Characteristics Typical Application circuit Figure 1, VIN = 3.6V, L = 10µH, D =
CMMSHI-40, CIN = 10µF, COUT = 1µF , TA = 25˚C , Unless otherwise Stated. (Continued)
LM3520
Typical Performance Characteristics Typical Application circuit Figure 1, VIN = 3.6V, L = 10µH, D =
CMMSHI-40, CIN = 10µF, COUT = 1µF , TA = 25˚C , Unless otherwise Stated. (Continued)
Typical PFM Switching Waveform
(Vin = 3.6V, at 30mA Load Current)
Typical PFM Switching Waveform
(Vin = 3.6V at 4mA Load Current)
20128838
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20128840
10
The LM3520 is designed for White LED & OLED backlighting
in mobile phone applications. It has a main display loop
which can drive up to 5 white LEDS in series and a sub
display loop which is designed to drive OLED up to 20V/50
mA. The main display loop employs a fixed frequency current mode scheme to regulate the LED current. The sub
display loop employs a fixed frequency gated oscillator
scheme to regulate the output voltage. The device has two
independent control pins to enable the Main or Sub displays.
Note that both displays can not be ON at the same time.
Under Voltage Protection
The LM3520 has an UVP comparator to turn the NMOS
power device off in case the input voltage or battery voltage
is too low preventing an on state of the power device conducting large amounts of current.
PWM Operation
Reliability and Thermal Shutdown
The LM3520 utilizes a synchronous Current Mode PWM
control scheme to regulate the feedback voltage over all load
and line conditions for the main display. The LM3520 is
internally compensated preventing the need for external
compensation components yielding a compact solution. The
operation can best be understood referring to the functional
block diagram. The LM3520 operates as follows: During the
first cycle, the oscillator sets the driver logic and turns on the
NMOS power device conducting current through the inductor
and reverse biases the external diode isolating the output
from the VSW node.
The LED current is supplied by the output capacitor when
the NMOS power device is active. During this cycle, the
output voltage of the EAMP controls the current through the
inductor. This voltage will increase for larger loads and decrease for smaller loads limiting the peak current in the
inductor. The sum of the EAMP voltage and voltage ramp is
compared with the sensed switch voltage. Once these voltages are equal, the PWM COMP will then reset the logic
turning off the NMOS power device and forward biasing the
external diode to the white LED load and flows through the
diode to the white LED load and output capacitor. The inductor current recharges the output capacitor and supplies the
current for the white LED branches. The oscillator then sets
the driver logic again repeating the process.
The LM3520 has an internal thermal shutdown function to
protect the die from excessive temperatures. The thermal
shutdown trip point is typically 160˚C, Normal operation resumes when the temperature drops below 140˚C.
Startup
The LM3520 does not include a power on reset circuit and
relies on external signal to monitor enable signal. In the
event of under voltage condition, the device enable pin must
be brought low until the input voltage is above the minimum
guarantee voltage (2.7V).
Application Information
SETTING LED CURRENT
The White LED current is set using the following equation:
For main display:
(1)
PWM CONTROL
The LED current can be controlled using a PWM signal on
the enable pin with frequencies in the range of 100 Hz to
1 kHz. LM3520 LED current can be controlled with PWM
signal frequencies above 1 kHz but LED current is not
linearly porportional to the duty cycle. The maximum LED
current would be achieved using the equation above with
100% duty cycle, ie. The enable pin is always high.
PFM Operation
The LM3520 utilizes a gated oscillator control scheme for the
sub-display. There is a hysteresis window to regulate the
output voltage. The oscillator frequency is the same as the
frequency in PWM control. The Duty cycle of the oscillator
signal is always set to maximum. During the first part of each
switching cycle, the internal NMOS switch is turned on until
the PFM current limit is reached. When the NMOS is off, the
voltage of the inductor reverses and forces current through
the diode to the output capacitor. This process continues
until the upper comparator hysteresis is reached at which
point the NMOS is disabled until the lower comparator
threshold is reached and the process repeats again.
SETTING SUB VOLTAGE
Sub-display voltage is be set by choosing RSUB1 and RSUB2
as illustrated in Figure 4. VSUB is calculated as follow:
Current Limit Protection
The LM3520 has current limiting protection to prevent excessive stress on itself and external components during overload conditions. The internal current limit comparator will
disable the NMOS power device at a typical switch peak
current limit of 700 mA.
(2)
Output Over-Voltage Protection
The LM3520 contains dedicated circuitry for monitoring the
output voltage. In the event that the primary LED network is
disconnected the output will increase and be limited to 23.2V
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LM3520
(typ.). There is a ~1V hysteresis associated with this circuitry, which will turn the NMOS off when the output voltage
is at 24.2V(max.) until the output voltage reach 22.5V(typ.)
or lower. The 23.5V limit allows the use of 25V 1 µF ceramic
output capacitors creating an overall small solution for white
LED applications.
Circuit Description
LM3520
Application Information
enable pins should not be ON at the same time during
normal operation. If for any reason, the main and Sub enable
are high, the main display will enable by default and the sub
display will disable by default. The following truth table summarize the logic state.
(Continued)
TABLE 1.
Main_EN
Sub_EN
Main
Sub
0
0
OFF
OFF
0
1
OFF
ON
1
0
ON
OFF
1
1
ON
OFF
INDUCTOR SELECTION
The inductor used with LM3520 must have a saturation
current greater than the device switch peak current limit.
Choosing inductors with low DCR decreases power losses
and increases efficiency. A 10 µH inductor is optimal for the
applications. If a smaller inductor is used, the larger the
inductor ripple current. Care must be taken to select the
inductor such that the peak current rating of the inductor
accounts for maximum load current for the operating condition. It is best to select an inductor with a peak current rating
of the maximum switch peak current of the device. The
following equation is useful for determining the inductor
value for a given application condition. Where IOUT_MAX =
maximum output load current, VOUT = output voltage, VIN_MIN = minimum input voltage, VDIODE = diode forward voltage, IPeak = Peak Current and fmax = maximum switch frequency.
20128805
FIGURE 4.
The above equation to solve for RSUB1 .
(3)
RSUB1 = (VSUB/VSUB_FB – 1)RSUB2
The LM3520 is optimized for 20V at 30 mA over the input
voltage range, for higher output current up to 50mA is
achieveable with a minimum input of 3.6V. If lower VSUB is
desired, the output current capability will be higher.
Using VSUB in Current Mode Configuration
If Vsub is used to drive a string of LEDs, instead of using
figure 3 configuration (voltage mode). The LEDs can be
arranged in current mode configuration to control load current.
TABLE 2.
Suppliers
www.coilcraft.com
Cooper Bussmann
www.cooperET.com
Murata
www.murata.com
DIODE SELECTION
To maintain high efficiency, the average current rating of the
schottky diode should be larger than the peak inductor current. Schottky diodes with a low forward drop and fast
switching speeds are ideal for increasing efficiency in portable applications. Choose a reverse breakdown of the
schottky diode larger than the output voltage. Some recommended diodes are MBR0530T1 from ON semiconductor
and CMMSHI-40 from Central Semiconductor.
20128801
FIGURE 5.
CAPACITOR SELECTION
Choose low ESR capacitors for the output to minimize output
voltage ripple. Ceramic capacitors such as X5R and X7R are
recommended for use as input and output filiters. These
capacitors provide an ideal balance between small size,
cost, reliability and performance. Do not use Y5V ceramic
capacitors as they have poor dielectric performance over
temperature and poor voltage characteristic for a given
value. For most applications, a 1 µF ceramic output capaci-
MAIN & SUB ENABLE
The LM3520 has two independent enable pins to control the
main and sub displays. A high on the Main Enable signal will
enable the main display. While a high on the Sub Enable pin
will enable the sub display. The PFM_EN pin must tied to
SUB_EN for enabling the Sub display. Both Main & Sub
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12
LM3520
Application Information
TABLE 3.
(Continued)
Suppliers
tor is sufficient for the main-display. A minimum of 4.7µF
output capacitor is recommended for VSUB output. Larger
output capacitor can be used to reduce ripple voltage. The
LM3520 has a maximum OVP of 24.2V, a 25V minimum
rated capacitor voltage is recommended for the application
to ensure proper biasing.
Local bypassing for the input is needed on LM3520. Multilayer ceramic capacitors with low ESR are a good choice for
this as well. A 10 µF capacitor is sufficient for most applications. Using larger capacitance decreases input voltage
ripple on the input. Extra attention is required if smaller case
size capacitor is used in the application. Smaller case size
capacitor typically has less capacitance for a given bias
voltage as compared to a larger case size capacitor with the
same bias voltage. Please contact the capacitor manufacturer for detail information regarding capacitance verses
case size. Table 3 lists several capacitor suppliers.
Website
TDK
www.tdk.com
AVX
www.avxcorp.com
Murata
www.murata.com
LAYOUT CONSIDERATIONS
As for any high frequency switcher, it is important to place
the external components as close as possible to the IC to
maximize device performance. Below are some layout recommendations: 1) Place input filter and output filter capacitors close to the IC to minimize copper trace resistance
which will directly effect the overall ripple voltage. 2) Place
the feedback network resistors in the Main and Sub display
close to the IC. 3) Route noise sensitive trace away from
noisy power components. 4) Connect the ground pins and
filter capacitors together via a ground plane to prevent
switching current circulating through the ground plane. Similarly the ground connection for the feedback network should
tie directly to GND plane. If no ground plan is available, the
ground connections should tie directly to the device GND
pin. Additional layout consideration regarding the LLP package can be found in Application AN1187
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LM3520 Integrated White LED Driver with Organic LED Display Power Supply
Physical Dimensions
inches (millimeters) unless otherwise noted
14–Pin LLP
NS Package Number SDA14A
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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