LINEAR TECHNOLOGY LT3519 Technical data
L DESIGN IDEAS
SW
V
IN
V
REF
CTRL
SHDN/UVLO
ISP
ISN
FB
OPENLED
ANODE
LT3519
GND
68µH
1M
V
IN
6V TO 30V
243k
137k
100k
1M
1M
29.4k
M1
2.49Ω
4.7µF
1µF
38V LED
100mA
CATHODE
PWM
PWM
V
OUT
SW
V
IN
V
REF
CTRL
SHDN/UVLO
ISP
ISN
FB
OPENLED
ANODE
LT3519
GND
L1A
68µH
C3
2.2µF
1M
V
IN
4V TO 24V
432k
158k
100k
1M
1M
69.8k
M1
R
SENSE
1.68Ω
C2
4.7µF
C1
1µF
16V LED
150mA
CATHODE
PWM
PWM
t
L1B
68µH
t
C1: TDK C3216X7R1H105K
C2: TDK C3216X7R1E475K
C3: TDK C3216X7R1E225K
L1: COILTRONICS DRQ74-680-R (COUPLED INDUCTOR)
M1: VISHAY SILICONIX Si2318DS
NOTE:
V
IN
= 6V RISING TURN ON
V
IN
= 4V FALLING UVLO
V
IN
> 9V FULL LED CURRENT AND FOLDBACK BELOW
V
OUT
18.5V OVERVOLTAGE PROTECTION
V
OUT
5V
PWM
5V/DIV
I
LED
0.1A/DIV
I
L
0.3A/DIV
2µs/DIVV
IN
= 12V
4W LED Driver Includes Power Switch,
Compensation Components and
Schottky in 16-Pin MSOP
Introduction
As the number of applications for
medium power (1W–4W) LED strings
grows, so does the need for compact, efficient, high performance LED drivers.
The LT3519 LED driver satisfies the
needs of a wide variety of applications,
including LCD displays, automotive
and avionic applications, architectural and industrial lighting, portable
projection and scanners. It’s 16-pin
MSOP package includes accurate LED
current regulation, small size, high
efficiency, PWM and analog dimming
for brightness control and open circuit
protection with fault detect.
Easy Layout: Integrated
Power Switch, Compensation
Components and Schottky
The 400kHz LT3519 LED driver features an integrated 750mA 45V peak
power switch, integrated compensation components and an integrated
low leakage Schottky diode, making
designs simple and small. Despite
this high level of integration, it can be
used in a wide variety of topologies,
including boost, SEPIC, buck mode
or buck-boost mode. For maximum
versatility, the Schottky diode anode
(ANODE) and internal power switch
emitter (SW) pins are separately pinned
out, so a SEPIC coupling capacitor can
be inserted between these two.
The internal compensation compo-
nents are chosen to match the 2.2µF
Figure 2. Integrated PWM dimming yields
1000:1 dimming at 120Hz
36
36
by Keith Szolusha
Figure 1. A 4W boost LED driver with 89% efficiency at 12V
to 4.7µF output capacitors in all of
the topologies mentioned above. The
integrated compensation network
all that is needed to assert the open
collector OPENLED output pin during
a fault.
combined with current mode control yields fast and stable transient
response.
OPENLED detection and fault reporting are included. A simple resistor
divider sets the overvoltage protection
output voltage in case of an open LED
string and a small pull-up resistor is
Figure 3. A SEPIC LED driver with short-circuit protection
4W Boost LED Driver
The simple boost LED driver in Figure
1 drives up to 38V of LEDs at 100mA
from an automotive input voltage
range. The 400kHz switching frequency is common for automotive, avionic
and industrial solutions; it combines
Linear Technology Magazine • September 2009
IN
continued on page 39
two regulators drive equal output cur-
GND
CLKOUT1 CLKIN2
V
IN1
SV
IN1
RUN1
PLLLPF1
MODE1
PHMODE1
TRACK1
V
IN2
SV
IN2
RUN2
MODE2
PHMODE2
TRACK2
V
OUT1
FB1
ITH1
ITHM1
MGN1
V
OUT2
FB2
ITH2
ITHM2
MGN2
V
OUT
1.8V
16A MAX
C3
22µF
x2
C4
100µF
x4
V
IN
3.3V to 5V
C1
22µF
x2
C2
150µF
R
SET
2.49k
LTM4616
(15mm s 15mm s 2.8mm)
LOAD CURRENT (A)
0
EFFICIENCY (%)
50
40
30
80
70
60
18
20
10
0
2 4 6 8 10 12 14 16
100
90
3.3V
IN
5V
IN
0A
TIME (2ms/DIV)
OUTPUT CURRENT (2A/DIV)
0A
I
OUT1
I
OUT2
rent even during soft-start, as shown
in Figure 5.
Conclusion
Whether you require a single 16A high
current output or dual 8A outputs with
sequencing, the LTM4616 provides a
simple and efficient solution.
L
Figure 3. LTM4616 with 16A parallel operation
Figure 5. Balanced current sharing for even
heat dissipation [5VIN to 1.8V
DESIGN IDEAS L
at 16A]
OUT
LT3519, continued from page 36
high efficiency, small inductor and
capacitor size, and high PWM dimming
capability while avoiding frequencies
in the AM broadcast band. A small
inductor with about 750mA saturation current rating, a few ceramic
capacitors and several tiny resistors
are all that are needed to complete the
design. As shown in Figure 2, the tiny
PWM dimming MOSFET can be used
to provide over 1000:1 pwm dimming
at 120Hz using the integrated LT3519
PWM dimming architecture and an
extremely low leakage integrated
Schottky diode.
A 1000:1 dimming ratio at 120Hz
is exceptionally high for a 400kHz
switching regulator. It can be tempting to bump up the dimming ratio by
choosing a higher frequency driver,
since in general, higher switching
frequency corresponds to higher
PWM dimming ratios. In this case,
avoiding the AM band means jumping
Linear Technology Magazine • September 2009
Figure 4. Efficiency: single 1.8V output
to 2MHz, which in the end reduces
the maximum duty cycle and the
efficiency. The 400kHz switching
frequency of the LT3519 does what
2MHz converters cannot do: it provides
high duty cycle for operation down to
6VIN with 38V
and as high as 89%
LED
efficiency at 12VIN. If PWM dimming
is not needed, the MOSFET M1 can
be removed and the analog dimming
(CTRL) pin can be used to adjust the
regulated LED current below 100mA
for simple brightness control.
2.4W SEPIC LED Driver
When the LED string voltage is within
the input rail voltage range, a SEPIC
topology is called for. The SEPIC produces a high PWM dimming ratio and
also gives short-circuit protection. The
SEPIC in Figure 3 drives 16V LEDs at
150mA from a 4V to 24V input range.
Since the anode of the integrated catch
diode (ANODE) is made available at
a pin independent of the npn power
switch emitter (SW), the coupling
capacitor is easily inserted between
the two. The maximum voltage that
the SW pin sees is a little above the
input voltage plus the output voltage,
so the 45V 750mA integrated power
switch is a perfect match for these
specifications.
Conclusion
The 400kHz LT3519 is a 4W LED
driver that integrates a number of
required components, including a 45V,
750mA power switch, a low leakage
Schottky diode and compensation
components. It also features PWM
dimming, overvoltage protection and
OPENLED fault detection, making it a
small, simple, and efficient choice for
automotive, avionic, industrial and
other LED driver applications.
L
3939
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