LM3519
LM3519 High Frequency Boost White LED Driver with High-Speed PWM
Brightness Control
Literature Number: SNVS394A
LM3519
High Frequency Boost White LED Driver with
High-Speed PWM Brightness Control
General Description
The LM3519 drives up to 4 white LEDs with constant current
to provide LCD backlighting in handheld devices. The LED
current is internally set to 20mA. The series connection
allows the LED current to be identical for uniform brightness
and minimizes the number of traces to the LEDs. Brightness
control is achieved by applying a PWM signal on enable with
frequencies up to 30kHz.
The LM3519 features a proprietary PFM regulation architec-
ture with switching frequencies between 2MHz to 8MHz,
minimizing inductor size.
Over-voltage protection circuitry and high frequency opera-
tion permit the use of low-cost small output capacitors. Dur-
ing shutdown, the output is disconnected from the input in
order to avoid leakage current path through the LEDs to
ground.
The LM3519 is available in a tiny 6-pin SOT23 package.
Features
nDrives 2 to 4 LEDs at 20mA
nUp to 30kHz PWM Dimming Control Capability
n>80% Peak Efficiency
nUp to 8MHz Switching Frequency
nSmall External Components: 1µH - 3.3µH(typ.2.2µH)
Inductor and 1µF Output Capacitor
nTrue Shutdown Isolation
nOver-Voltage Protection
nWide Input Voltage Range: 2.7V to 5.5V
nSmall Footprint SOT23-6 Package
Applications
nLCD, White LED Backlighting on Mobile Phones
nDigital Still Cameras and PDAs
nGeneral Purpose LED Lighting in Handheld Devices
Typical Application
20160201
FIGURE 1. Typical Application Circuit
September 2005
LM3519 High Frequency Boost White LED Driver with High-Speed PWM Brightness Control
© 2005 National Semiconductor Corporation DS201602 www.national.com
Connection Diagram
6-Lead SOT23 Package
20160202
Top View
Pin Descriptions
Pin # Name Description
1 En Device Enable Connection
2 Gnd Ground Connection
3V
OUT
Output Voltage Connection
4 LED_rtn White LED Current Sensing Input Connection
5S
W
Drain Connection of the Internal Power Field Effect Transistor (FET) Switch
6V
IN
Input or Supply Voltage Connection
Ordering Information
Current
Option Order Number
Package
Marking Supplied As
20 mA LM3519MK-20 D52B 1000 Units, Tape-and-Reel
LM3519MKX-20 D52B 3000 Units, Tape-and-Reel
LM3519
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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
, En, & LED_rtn Pin −0.3V to +6.5V
V
OUT
, Sw Pin −0.3V to +21V
Maximum Junction Temperature
(T
J-MAX
) +150˚C
Storage Temperature Range −65˚C to +150˚C
ESD Rating (Note 2)
Human Body Model:
Machine Model:
2kV
200V
Operating Ratings
Junction Temperature (T
J
) Range −40˚C to +125˚C
Ambient Temperature (T
A
) Range −40˚C to +85˚C
Input Voltage Range 2.7V to 5.5V
Thermal Properties (Note 4)
Junction-to-Ambient Thermal Resistance (θ
JA
) 220˚C/W
Electrical Characteristics (Note 5) Limits in standard typeface are for T
J
= +25˚C. Limits in bold typeface
apply over the full operating junction temperature range (−40˚C ≤T
J
≤+125˚C). V
IN
= 3.6V, unless otherwise stated.
Symbol Parameter Conditions Min Typ Max Units
I
Q
Supply Current
Shutdown: V
EN
= 0V 0.1
µA
Not Switching: V
EN
= 1.8V 360 500
Switching: V
EN
= 1.8V,
LED_rtn current = 30mA 550 900
I
LED(TOL)
LED Current
Tolerance/Variation
V
IN
= 3.6V, 2.2µH,
4LEDs –10 5.5 10 %
OVP Over-Voltage Protection
Threshold
OVP ON
OVP OFF
18
17.8
18.9
18.6
20
19.8 V
I
LIM
Switch Current Limit L = 2.2µH 750 mA
R
DS(ON)
Power NMOS Switch ON
Resistance 455 mΩ
I
LEAKAGE
Switch Leakage V
SW
= 3.6V, V
EN
= 0V 0.1 2µA
R
LED_rtn(ON)
LED_rtn NMOS Switch
ON Resistance 8.0 Ω
F
S
Switching Frequency I
LED
=20mA,L=1µH
4LEDs 5.4 MHz
I
EN
Enable Pin Bias Current
(Note 3)
V
EN
=0V
V
EN
= 1.8V
0.1
1.1 2µA
En Enable Threshold Device On
Device Off
0.9
0.3 V
Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the
device is guaranteed. Operating Ratings do not imply guaranteed limits. For guaranteed performance limits and associated test conditions, see the Electrical
Characteristics table.
Note 2: The human body model is a 100pF capacitor discharged through a 1.5kΩresistor into each pin. The machine model is a 200pF capacitor discharged directly
into each pin.
Note 3: Current flows into the pin.
Note 4: The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(MAX), the junction-to-ambient thermal resistance, θJA,
and the ambient temperature, TA. See Thermal Properties for the thermal resistance. The maximum allowable power dissipation at any ambient temperature is
calculated using: PD(MAX) = (TJ(MAX) – TA)/θJA. Exceeding the maximum allowable power dissipation will cause excessive die temperature.
Note 5: Min and max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm.
LM3519
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Block Diagram
20160203
FIGURE 2. Block Diagram
LM3519
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Circuit Description
The LM3519 is a step-up converter for white LED applica-
tions that uses a unique and proprietary pulse frequency
modulation (PFM) architecture to optimize high efficiency at
high frequency operation. Unlike most PFM architecture
implementations, the LM3519’s unique architectural imple-
mentation results in non-pulse skipping variable frequency
operation. The regulator is forced to operate at the edge of
Continous Conduction Mode (CCM). The error amplifier will
set the end of the on-time (I
PEAK
of inductor) based on the
load (LEDs) current. During this operation, the inductor cur-
rent ramps up and reaches a peak current at end of the
on-time. At this point, the internal power switch is turned off
until the inductor current reaches zero, and the cycle repeats
again. The switching frequency is set based on the charge
(on-time) and discharge(off-time) of the inductor current. The
frequency can range between 2MHz to 8MHz over the op-
erating input range.
The LM3519 operation can be best understood through an
examination of the block diagram in Figure 2. When LED
current is out of regulation, the LED_rtn voltage falls below
or rises above the internal reference voltage (VREF). The
error amplifier will output a signal to increase or decrease the
proper on-time duration of N1 power FET. This correction
allows the inductor’s stored energy to increase or decrease
to a sufficient level that when transferred to the load will bring
the LED_rtn current back into regulation.
During steady-state operation for a typical switching cycle,
the oscillator sets the driver logic and turns on N1 power
device. N1 conducts current through the inductor and re-
verse biases the external diode. The LED current is supplied
by the output capacitor when N1 is conducting. Once N1
on-time period is concluded, the internal power device is
turned off and the external diode is forward baised. The
inductor current then flows through the diode to the LED load
to replenish the output capacitor and keep the LED current
regulated at the trimmed target.
LM3519
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Typical Performance Characteristics (See Typical Application Circuit : V
IN
= 3.6V, C
IN
= 4.7µF and
C
OUT
= 1µF, L = 2.2µH and 4 LEDs. T
A
= +25˚C, unless otherwise stated.)
Efficiency vs V
IN
Efficiency vs V
IN
20160251 20160231
Efficiency vs V
IN
Efficiency vs V
IN
20160232 20160233
I
OUT_ACCURACY
vs V
IN
I
OUT_ACCURACY
vs V
IN
20160249 20160250
LM3519
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Typical Performance Characteristics (See Typical Application Circuit : V
IN
= 3.6V, C
IN
= 4.7µF and
COUT = 1µF, L = 2.2µH and 4 LEDs. T
A
= +25˚C, unless otherwise stated.) (Continued)
I
OUT
vs V
IN
I
OUT
vs V
IN
20160234 20160235
I
OUT
vs V
IN
I
OUT
vs PWM Duty Cycle
(V
IN
= 3.6V, L = 2.2µH)
20160253 20160260
I
OUT
vs PWM Duty Cycle
(V
IN
= 3.6V, L = 2.2µH)
I
OUT
vs PWM Duty Cycle
(V
IN
= 3.6V, L = 1µH)
20160261 20160259
LM3519
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Typical Performance Characteristics (See Typical Application Circuit : V
IN
= 3.6V, C
IN
= 4.7µF and
COUT = 1µF, L = 2.2µH and 4 LEDs. T
A
= +25˚C, unless otherwise stated.) (Continued)
I
OUT
vs PWM Duty Cycle
(V
IN
= 3.6V, L = 1µH) Switching Frequency vs V
IN
20160244 20160207
Switching Frequency vs V
IN
Switching Frequency vs V
IN
20160209 20160245
Switching Frequency vs V
IN
Peak Inductor Current vs V
IN
20160246 20160204
LM3519
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Typical Performance Characteristics (See Typical Application Circuit : V
IN
= 3.6V, C
IN
= 4.7µF and
COUT = 1µF, L = 2.2µH and 4 LEDs. T
A
= +25˚C, unless otherwise stated.) (Continued)
Peak Inductor Current vs V
IN
Peak Inductor Current vs V
IN
20160206 20160208
Current Limit vs V
IN
(4LEDs, 1µH) Current Limit vs V
IN
20160247 20160248
Iq (non switching) vs Temperature Iq (switching) vs Temperature
20160255 20160256
LM3519
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Typical Performance Characteristics (See Typical Application Circuit : V
IN
= 3.6V, C
IN
= 4.7µF and
COUT = 1µF, L = 2.2µH and 4 LEDs. T
A
= +25˚C, unless otherwise stated.) (Continued)
LED Switch R
DS_ON
vs Temperature Power Switch R
DS_ON
vs Temperature
20160257 20160258
Start-up, (V
IN
= 3.6V, 4LEDs, 2.2µH) Start-up (V
IN
= 3.6V, 4LEDs, 3.3µH)
20160210 20160219
Start-up (V
IN
= 3.6V, 2LEDs, 3.3µH) Start-up, (V
IN
= 3.6V, 2LEDs, 2.2µH)
20160220 20160211
LM3519
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Typical Performance Characteristics (See Typical Application Circuit : V
IN
= 3.6V, C
IN
= 4.7µF and
COUT = 1µF, L = 2.2µH and 4 LEDs. T
A
= +25˚C, unless otherwise stated.) (Continued)
Typical Switching Waveform
(V
IN
= 3.6V, 4LEDs, 3.3µH)
Typical Switching Waveform
(V
IN
= 3.6V, 4LEDs, 2.2µH)
20160218 20160212
Typical Switching Waveform
(V
IN
= 3.6V, 3LEDs, 2.2µH)
Typical Switching Waveform
(V
IN
= 3.6V, 2LEDs, 2.2µH)
20160214 20160215
Typical Switching Waveform
(V
IN
= 3.6V, 3LEDs, 1µH)
Typical Switching Waveform
(V
IN
= 3.6V, 4LEDs, 1µH)
20160228 20160229
LM3519
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Application Information
CAPACITOR SELECTION
To minimize output and input voltage ripple, low equivalent
series resistance (ESR) ceramic capacitors are the best
choice to use for the input and output filters. For most display
applications, a 4.7µF capacitor is recommended for C
IN
and
1µF for C
OUT
.
Larger output capacitors can be used to reduce ripple volt-
age. To guarantee good performance, a minimum of 0.47µF
C
OUT
is required to trade off for large ripple voltage. Care
must be taken to account for the true capacitance of a
multilayer ceramic capacitor. Smaller case size capacitors
typically have less capacitance for a given bias voltage as
compared to a larger case size capacitor with the same bias
voltage. Please confirm with capacitor manufacturer data
before selecting the capacitor.
Some recommended capacitor manufacturers include but
are not limited to:
Manufacturer Description Case Size
AVX 06033D105MAT-25V 0603
06036D475MAT-6.3V 0603
TDK C2012X5R1A475M-10V 0805
Taiyo Yuden TMK212BJ105KG-J 0805
EM212BJ475MG-16V 0805
muRata GRM40-034B105K25 0805
GRM39X5R475K6.3 0603
INDUCTOR SELECTION
In order to maintain sufficient inductance, the saturation
current rating of the inductor used with the LM3519 should
be higher than the peak inductor current in the target appli-
cation. Inductors with low DCR values have less power loss
and higher efficiency. Larger inductor values such as 2.2µH
and 3.3µH can be used to optimize efficiency, frequency and
peak current. If 1µH is used, the peak inductor current,
frequency will be higher and the efficiency will be lower. Note
that the switching frequency ranges will be higher at lower
inductance. Typical frequency range is between 4 to 8MHz
for 1µH, 2 to 5MHz for 2.2µH and 2 to 4MHz for 3.3µH over
the input range. Below is a sample list of low profile induc-
tors.
Some recommended inductor manufacturers include but
are not limited to:
Manufacturer L Case Size I
SAT
CoilCraft:
DO3314-102 1µH
3.3x3.3x1.4mm
2.1A
DO3314-222 2.2µH 1.6A
DO3314-332 3.3µH 1.4A
Coilcraft:
LPO3310-102ML 1µH
3.3x3.3x1.0 mm
1.6A
LPO3310-222ML 2.2µH 1.1A
LPO3310-332ML 3.3µH 0.95A
Cooper:
SD31121R0 1µH
3.1x3.1x1.4 mm
2.07A
SD3114-2R2 2.2µH 1.48A
SD3114-3R3 3.3uH 1.15A
Taiyo Yuden:
NR3015T1R0N 1µH
3.0x3.0x1.5 mm
2.1A
NR3015T2R2M 2.2µH 1.48A
NR3015T3R3M 3.3µH 1.21A
DIODE SELECTION
Diodes with low forward voltage ratings (V
F
) and low junction
capacitance magnitudes (C
J
or C
T
or C
D
) are conducive to
high efficiency. The chosen diode must have a reverse
breakdown voltage rating (V
R
and/or V
RRM
) that is larger
than the output voltage. The following criteria should be
followed when choosing a diode:
1. V
R
(Diode Blocking Voltage Range) and V
RRM
(Diode
Peak Repetitive Reverse Voltage Rating) >V
OUT
(Out-
put Voltage)
2. I
F
or I
O
(Diode Average Forward Current Rating) ≥I
LOAD
(Load Current)
3. I
FRM
(Diode Peak Repetitive Forward Current Rating) ≥
I
Lpeak
(Peak Inductor Current)
Some recommended diode manufacturers include but are
not limited to:
Maufacturer Description
Vishay SS12(1A/20V)
SS14(1A/40V)
SS16(1A/60V)
Central Semiconductor CMSH1- 40M(1A/40V)
ONSemi MBRS1540T3(1.5A/40V)
PWM DIMMING
The LED current is set internally by the LM3519 to 20mA
(typical); dimming control may be realized by applying a
pulse width modulated(PWM) signal to the En pin. For ex-
ample, a 50% duty cycle waveform will produce an average
current of 10mA. A control signal frequency between 17kHz
and 30kHz is suitable for dimming.
Although the LM3519 is capable of operation outside this
frequency range, it is not recommended to operate below
17kHz for the following reasons: 1) frequency below 100Hz
is likely to cause visible flicker in the light emitted by the LED
string. 2) frequency below 17kHz may induce audible noise
due to combinations of some capacitance/PCB. A PWM
frequency above 30kHz is possible but the current linearity
vs duty cycle will be affected.
If it is not possible to operate the dimming control above
17kHz, audible noise emission may be minimized by using
capacitors with low susceptibility to piezoelectric induced
stresses, such as poly film designs. Minimum audible noise
is most likely to occur when the PWM frequency is less than
2kHz. It is recommended that any application using a PWM
control signal below 17kHz be thoroughly evaluated for un-
desirable audible or visible noise.
DRIVING 2 LEDs
The LM3519 is optimized to drive up to 4LEDs. When driving
2LEDs, a minimum inductance of 2.2µH is required to main-
tain good loop regulation and current accuracy. If a smaller
inductor is used, the LED current will have more variation
with input voltage than a typical application. The following
curve illustrates the behavior.
LM3519
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Application Information (Continued)
I
OUT
vs V
IN
20160239
LAYOUT GUIDELINES
The input capacitor, C
IN
, must be placed close to the
LM3519. Placing C
IN
close to the device will reduce the
metal trace resistance effect on input voltage ripple. Metal
trace connections for the C
OUT
capacitor can increase the
effective series resistance, which affects output voltage
ripple and efficiency. Trace connections to the inductor
should be short and wide to reduce power dissipation, in-
crease overall efficiency and reduce EMI radiation. The di-
ode, like the inductor, should have trace connections that are
short and wide to reduce power dissipation and increase
overall efficiency. For more details regarding layout guide-
lines for switching regulators, refer to Applications Note AN-
1149.
LM3519
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Physical Dimensions inches (millimeters) unless otherwise noted
6-Lead SOT23-6 Package
NS Package Number MK06A
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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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS
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(b) support or sustain life, and whose failure to perform when
properly used in accordance with instructions for use
provided in the labeling, can be reasonably expected to result
in a significant injury to the user.
2. A critical component is any component of a life support
device or system whose failure to perform can be reasonably
expected to cause the failure of the life support device or
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LM3519 High Frequency Boost White LED Driver with High-Speed PWM Brightness Control
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