LT3519/LT3519-1/LT3519-2 - LED Driver with Integrated Schottky Diode

LT3519/LT3519-1/LT3519-2
LED Driver with Integrated
Schottky Diode
FEATURES
n
n
n
n
n
n
n
n
n
n
n
n
n
n
DESCRIPTION
Up to 3000:1 True Color PWM™ Dimming
Wide Input Voltage Range
Operation from 3V to 30V
Transient Protection to 40V
Rail-to-Rail LED Current Sense from 0V to 45V
45V, 750mA Internal Switch
Internal Schottky Diode
Constant-Current and Constant-Voltage Regulation
Boost, SEPIC, Buck-Boost Mode or Buck Mode
Topology
Open LED Protection and Open LED Status Pin
Programmable Undervoltage Lockout with Hysteresis
Fixed Frequency: 400kHz (LT3519), 1MHz (LT3519-1),
2.2MHz (LT3519-2)
Internal Compensation
CTRL Pin Provides Analog Dimming
Low Shutdown Current: <1μA
16-Lead MSOP Package
The LT®3519/LT3519-1/LT3519-2 are fixed frequency
step-up DC/DC converters designed to drive LEDs. They
feature an internal 45V, 750mA low side switch and Schottky
diode. Combining a traditional voltage feedback and a
unique rail-to-rail current sense feedback allows these
converters to operate as a constant-voltage source or
constant-current source. Internal compensation simplifies
applications. These devices feature rail-to-rail LED current
sense pins that provide the most flexibility in choosing a
converter configuration to drive the LEDs. The LED current is externally programmable with a sense resistor. The
external PWM provides up to 3000:1 PWM dimming and
the CTRL input provides analog dimming.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. True Color PWM is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 7199560 and 7321203.
APPLICATIONS
n
n
n
n
Automotive
Industrial
Constant Current Source
Current Limited Constant Voltage Source
TYPICAL APPLICATION
4W Boost Automotive LED Driver
VOUT
120
4.7μF
1μF
SW ANODE CATHODE
VIN
ISP
2.49Ω
1M
SHDN/UVLO
100k
1M
243k
VREF
ISN
1M
LT3519
CTRL
FB
38V LED
100mA
29.4k
137k
OPENLED
GND
VIN = 6V AND ABOVE
100
LED CURRENT (mA)
VIN
6V TO 30V
LED Current vs VIN
68μH
80
60
40
20
0
0
PWM
M1
10
20
30
VIN (V)
3519 TA01b
PWM
3519 TA01a
3519fa
1
LT3519/LT3519-1/LT3519-2
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
VIN, OPENLED (Note 3) .............................................40V
SHDN/UVLO (Note 4) ...............................................40V
SW, ISP , ISN, ANODE, CATHODE ..............................45V
PWM, CTRL ..............................................................10V
FB, VREF ......................................................................3V
Operating Junction Temperature Range
(Note 2).................................................. –40°C to 125°C
Maximum Junction Temperature........................... 125°C
Storage Temperature Range................... –65°C to 125°C
TOP VIEW
GND
OPENLED
PWM
SHDN/UVLO
VIN
SW
ANODE
GND
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
GND
VREF
CTRL
FB
ISN
ISP
CATHODE
GND
MS PACKAGE
16-LEAD PLASTIC MSOP
TJMAX = 125°C, θJA = 130°C/W
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3519EMS#PBF
LT3519EMS#TRPBF
3519
16-Lead Plastic MSOP
–40°C to 125°C
LT3519EMS-1#PBF
LT3519EMS-1#TRPBF
35191
16-Lead Plastic MSOP
–40°C to 125°C
LT3519EMS-2#PBF
LT3519EMS-2#TRPBF
35192
16-Lead Plastic MSOP
–40°C to 125°C
LT3519IMS#PBF
LT3519IMS#TRPBF
3519
16-Lead Plastic MSOP
–40°C to 125°C
LT3519IMS-1#PBF
LT3519IMS-1#TRPBF
35191
16-Lead Plastic MSOP
–40°C to 125°C
LT3519IMS-2#PBF
LT3519IMS-2#TRPBF
35192
16-Lead Plastic MSOP
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full
operating temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, SHDN/UVLO = 12V, CTRL = 2V, PWM = 5V,
unless otherwise noted.
PARAMETER
CONDITIONS
VIN Operating Voltage Range
Continuous Operation (Note 3)
MIN
VIN Supply Current
SHDN/UVLO = 0V
(Shutdown)
PWM = 0V
(Idle)
PWM > 1.5V, FB = 1.5V (Active, Not Switching)
Current Sense Voltage (VISP-VISN)
ISP = 24V
ISP = 0V
l
Zero Current Sense Voltage (VISP-VISN)
ISP = 24V, CTRL = 100mV
l
Current Sense Voltage Line Regulation
2.5V < ISP < 45V
TYP
3
MAX
UNITS
30
V
0.1
2.0
2.5
1
3.0
3.5
μA
mA
mA
240
250
250
260
mV
mV
–15
–6
3
mV
0.02
%/V
3519fa
2
LT3519/LT3519-1/LT3519-2
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full
operating temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, SHDN/UVLO = 12V, CTRL = 2V, PWM = 5V,
unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Switching Frequency
400kHz (LT3519)
1MHz
(LT3519-1)
2.2MHz (LT3519-2)
l
l
l
320
0.80
1.9
400
1
2.2
440
1.10
2.4
kHz
MHz
MHz
Maximum Duty Cycle
400kHz (LT3519)
1MHz
(LT3519-1)
2.2MHz (LT3519-2)
l
l
l
94
86
72
97
93
83
l
750
980
Switch Current Limit
Switch VCESAT
ISW = 500mA
Switch Leakage Current
SW = 45V, PWM = 0V
1150
300
mA
mV
2
CTRL for Full-Scale LED Current
CTRL Pin Bias Current
%
%
%
μA
1.2
Current Out of Pin, CTRL = 0.1V
V
50
PWM Input High Voltage
l
PWM Input Low Voltage
l
100
nA
0.8
V
1.5
PWM Pin Resistance to GND
V
70
l
FB Regulation Voltage (VFB)
FB Pin Threshold Voltage for OPENLED Falling
1.190
1.220
kΩ
1.250
V
VFB – 70mV VFB – 60mV VFB – 50mV
FB Pin Bias Current
Current Out of Pin, FB = 1V
ISP , ISN Idle Input Bias Current
PWM = 0V, ISP = ISN = 24V
ISP , ISN Active Input Bias Current
ISP = ISN = 24V, Current per Pin
17
μA
Schottky Forward Drop
ISCHOTTKY = 500mA
0.8
V
Schottky Leakage Current
CATHODE = 24V, ANODE = 0V
SHDN/UVLO Threshold Voltage Falling
60
V
l
SHDN/UVLO Input Low Voltage
IVIN Drops Below 1μA
SHDN/UVLO Pin Bias Current Low
SHDN/UVLO = 1.15V
SHDN/UVLO Pin Bias Current High
SHDN/UVLO = 1.30V
VREF Output Voltage
–100μA ≤ IVREF ≤ 0μA
1.180
1.8
l
1.96
120
nA
1
μA
4
μA
1.270
V
0.4
V
2.2
2.6
μA
10
100
nA
2
2.04
V
1.220
VREF Output Pin Regulation
3V < VIN < 40V
0.04
%/V
OPENLED Output Low (VOL)
IOPENLED = 1mA
240
mV
OPENLED Leakage Current
FB = 0V, OPENLED = 40V
1
μA
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2. The LT3519E/LT3519E-1/LT3519E-2 are guaranteed to meet
specified performance from 0°C to 125°C junction temperature range.
Specifications over the –40°C to 125°C operating junction temperature
range are assured by design, characterization and correlation with
statistical process controls. The LT3519I/LT3519I-1/LT3519I-2 are
guaranteed to meet performance specifications over the –40°C to 125°C
operating junction temperature range.
Note 3. Absolute maximum voltage at VIN and OPENLED is 40V for
nonrepetitive one second transients and 30V for continuous operation.
Note 4. For VIN below 6V, the SHDN/UVLO pin must not exceed VIN for
proper operation.
3519fa
3
LT3519/LT3519-1/LT3519-2
TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C unless otherwise noted)
Switch Current Limit
vs Duty Cycle
VISP-VISN Threshold vs VCTRL
VIN = 12V
VISP = 24V
SWITCH CURRENT LIMIT (mA)
VISP-VISN THRESHOLD (mV)
250
200
150
100
50
1.0
1.5
2.02
900
1.97
600
2.0
0
25
50
75
DUTY CYCLE (%)
1.96
–50
100
260
1200
250
248
246
244
100
125
Oscillator Frequency
vs Temperature (LT3519)
420
VIN = 12V
1100
410
FREQUENCY (kHz)
SWITCH CURRENT LIMIT (mA)
254
252
50
75
0
25
TEMPERATURE (°C)
3519 G03
Switch Current Limit
vs Temperature
VIN = 12V
VISP = 24V
VCTRL = 2V
–25
3519 G02
VISP-VISN Threshold
vs Temperature
VISP-VISN THREHSOLD (mV)
2.00
1.98
700
3519 G01
256
2.01
1.99
800
VCTRL (V)
258
VIN = 12V
2.03
1000
–50
0.5
2.04
1100
0
0
VREF Voltage vs Temperature
1200
VREF (V)
300
1000
900
800
700
400
390
380
370
242
240
–50
–25
100
50
25
0
75
TEMPERATURE (°C)
600
–50
125
–25
75
0
50
25
TEMPERATURE (°C)
VISP-VISN Threshold vs VISP
VREF Voltage vs VIN
100
125
Quiescent Current vs VIN
3.0
2.03
2.5
256
254
252
250
248
VIN CURRENT (mA)
2.02
VREF (V)
VISP-VISN THRESHOLD (mV)
50
25
75
0
TEMPERATURE (°C)
3519 G06
2.04
VIN = 12V
VCTRL = 2V
258
360
–50 –25
125
3519 G05
3519 G04
260
100
2.01
2.00
1.99
246
2.0
1.5
1.0
1.98
244
242
1.97
240
1.96
0
10
30
20
VISP (V)
40
50
0.5
0
5
10
15
20
25
30
35
40
VIN (V)
3519 G07
3519 G08
VPWM = 5V
VFB = 1.5V
0
0
10
20
VIN (V)
30
40
3519 G09
3519fa
4
LT3519/LT3519-1/LT3519-2
TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C unless otherwise noted)
FB OPENLED Threshold
vs Temperature
FB Regulation Voltage
vs Temperature
1.25
100
VIN = 12V
SHDN/UVLO Threshold
vs Temperature
1.30
VIN = 12V
90
VFB-VFB_OPENLED (mV)
VFB (V)
1.23
1.22
SHDN/UVLO THRESHLD (V)
80
1.24
70
60
50
40
30
20
1.21
VIN = 12V
1.28
SHDN/UVLO RISING
1.26
1.24
SHDN/UVLO FALLING
1.22
10
1.20
–50
–25
50
25
75
0
TEMPERATURE (°C)
100
0
–50
125
–25
50
25
0
75
TEMPERATURE (°C)
3519 G10
9
300
250
200
150
100
50
600
800
400
SWITCH CURRENT (mA)
1000
8
7
6
5
4
3
2
1
0
–50
–25
50
25
0
75
TEMPERATURE (°C)
3519 G13
125
100
125
800
700
600
500
400
300
200
100
0
0
1000
800
200
600
400
SCHOTTKY FORWARD VOLTAGE DROP (mV)
3519 G14
Oscillator Frequency
vs Temperature (LT3519-1)
3519 G15
Oscillator Frequency
vs Temperature (LT3519-2)
1.2
2.5
2.4
1.1
1.0
0.9
0.8
0.7
–50
100
Schottky Forward Voltage Drop
VR = 24V
FREQUENCY (MHz)
200
FREQUENCY (MHz)
SWITCH VOLTAGE (V)
350
50
25
75
0
TEMPERATURE (°C)
900
SCHOTTKY FORWARD CURRENT (mA)
450
SCHOTTKY LEAKAGE CURRENT (μA)
10
400
–25
3519 G12
Schottky Leakage Current
vs Temperature
500
0
1.20
–50
125
3519 G11
Switch Saturation Voltage
(VCESAT)
0
100
2.3
2.2
2.1
2.0
–25
0
25
75
50
TEMPERATURE (°C)
100
125
3519 G16
1.9
–50
–25
0
25
75
50
TEMPERATURE (°C)
100
125
3519 G17
3519fa
5
LT3519/LT3519-1/LT3519-2
PIN FUNCTIONS
GND (Pins 1, 8, 9, 16): Power Ground and Signal Ground.
Tie to GND plane for best thermal performance.
SW (Pin 6): Switch Pin. Connect the inductor at this pin.
Minimize the trace at this pin to reduce EMI.
OPENLED (Pin 2): Open LED Status Pin. The OPENLED
pin asserts if the FB input is greater than the FB regulation
threshold minus 60mV (typical). The pin must have an
external pull-up resistor to function. When the PWM input
is low and the converter is idle, the OPENLED condition
is latched to the last valid state when the PWM input was
high. When the PWM input goes high again, the OPENLED
pin will be updated. This pin may be used to report an
open LED fault.
ANODE (Pin 7): Internal Schottky Anode Pin.
PWM (Pin 3): Pulse Width Modulated Input. A signal
low disables the oscillator and turns off the main switch.
PWM has an internal pull-down resistor. Tie PWM pin to
VREF if not used.
SHDN/UVLO (Pin 4): Shutdown and Undervoltage Lockout
Pin. An accurate 1.22V falling threshold with externally
programmable hysteresis detects when power is okay to
enable switching. Rising hysteresis is generated by the
external resistor divider and an accurate internal 2.2μA
pull-down current. Above the 1.25V (nominal) rising
threshold (but below 6V), SHDN/UVLO input bias current
is sub-μA. Below the falling threshold, a 2.2μA pull-down
current is enabled so the user can define the hysteresis
with external resistor selection. Tie to 0.4V or less to disable device and reduce VIN quiescent current below 1μA.
Pin may be tied to VIN, but do not tie it to a voltage higher
than VIN if VIN is less than 6V.
VIN (Pin 5): Input Supply Pin. This pin must be locally
bypassed with a 1μF ceramic capacitor (or larger) placed
close to it.
CATHODE (Pin 10): Internal Schottky Cathode Pin.
ISP (Pin 11): Current Sense Resistor Positive Pin. This
input is the noninverting input of the internal current sense
amplifier. Input bias current increases with VISP –VISN
increase.
ISN (Pin 12): Current Sense Resistor Negative Pin. This
input is the inverting input of the internal current sense
amplifier.
FB (Pin 13): Voltage Loop Feedback Pin. It is used to
connect to output resistor divider for constant voltage
regulation or open LED protection. The internal transconductance amplifier will regulate FB to 1.22V (nominal)
through the DC/DC converter. If the FB input is regulating
the loop, the OPENLED pull-down is asserted. This action
may signal an open LED fault. Do not leave the FB pin
open. If not used, connect to GND.
CTRL (Pin 14): Current Sense Threshold Voltage Adjustment Pin. This pin sets the threshold voltage across the
sense resistor between ISP and ISN. Connect directly to
the VREF pin or a voltage above 1.2V for full-scale threshold of 250mV, or use a voltage between 0.1V and 1.0V to
linearly adjust the threshold. A voltage between 1.0V and
1.2V transitions to the full-scale threshold. Tie CTRL pin
to the VREF pin if not used.
VREF (Pin 15): Reference Output Pin. Typically 2V. This
pin can supply up to 100μA.
3519fa
6
LT3519/LT3519-1/LT3519-2
BLOCK DIAGRAM
LED ARRAY
COUT
RSENSE
L1
VIN
PWM
11
12
3
ISN
ISP
+
10
PWM
7
CATHODE
6
ANODE
SW
D1
–
VIN 5
s4
100mV
–+
1.1V
14
CTRL
–
+
+
CIN
A1
+
–
A3
+
+
1.22V
R1
13
FB
RC
ERROR
AMPLIFIER
A2
G3
MAIN SWITCH
DRIVER
CC
+
–
A4
G1
R
Q1
MAIN
SWITCH
G2
Q
S
PWM
COMPARATOR
R2
VIN
4
SHDN/UVLO
+
BANDGAP
AND
BIAS
+
2.2μA
–
G4
Q3
VIN
FB
+
1.16V
–
OSCILLATOR
140μA
15
GND
1, 8, 9, 16
RAMP
GENERATOR
–
1.22V
RS
A5
OPENLED
Q4
2
IQ4
VREF
–
92k
2V
+
A6
Q2
3519 BD
NOTE: THE MAXIMUM ALLOWED Q4 COLLECTOR CURRENT IQ4 IS 2mA.
3519fa
7
LT3519/LT3519-1/LT3519-2
OPERATION
The LT3519/LT3519-1/LT3519-2 are constant frequency,
current mode regulators with an internal power switch and
Schottky. Operation can be best understood by referring
to the Block Diagram. At the start of each oscillator cycle,
the SR latch is set, which turns on the Q1 power switch.
A voltage proportional to the switch current is added to
a stabilizing ramp and the resulting sum is fed into the
positive terminal of the PWM comparator, A4. When this
voltage exceeds the level at the negative input of A4, the
SR latch is reset, turning off the power switch. The level
at the negative input of A4 is set by the error amplifier A3.
A3 has two inputs, one from the voltage feedback loop and
the other one from the current loop. Whichever feedback
input is lower takes precedence to set the VC node voltage,
and forces the converter into either a constant-current or
a constant-voltage mode.
The LT3519/LT3519-1/LT3519-2 are designed to transition cleanly between these two modes of operation. The
current sense amplifier senses the voltage across RSENSE
and provides an ×4 pre-gain to amplifier A1. The output
of A1 is simply an amplified version of the difference between the voltage across RSENSE and the lower of VCTRL
or 1.1V. In this manner, the error amplifier sets the correct
peak switch current level to regulate the current through
RSENSE. If the error amplifier’s output increases, more
current is delivered to the output; if it decreases, less
current is delivered. The current regulated in RSENSE can
be adjusted by changing the input voltage VCTRL. The FB
voltage loop is implemented by the amplifier A2. When
the voltage loop dominates, the VC node voltage is set by
the amplified difference of the internal reference of 1.22V
and the FB pin. If FB voltage is lower than the reference
voltage, the switch current will increase; if FB voltage is
higher than the reference voltage, the switch demand
current will decrease. The LED current sense feedback
interacts with the FB voltage feedback so that FB will not
exceed the internal reference and the voltage between ISP
and ISN will not exceed the threshold set by the CTRL pin.
For accurate current or voltage regulation, it is necessary
to be sure that under normal operating conditions the
appropriate loop is dominant. To deactivate the voltage
loop entirely, FB can be connected to GND. To deactivate
the LED current loop entirely, the ISP and ISN should be
tied together and the CTRL input tied to VREF .
When the FB input exceeds a voltage about 60mV lower
than the FB regulation voltage, the pull-down driver on
the OPENLED pin is activated. This function provides a
status indicator that the load may be disconnected and
the constant-voltage feedback loop is taking control of
the switching regulator.
Dimming of the LED array is accomplished by pulsing the
current using the PWM pin. When the PWM pin is low,
switching is disabled and the error amplifier is turned off
so that it does not drive the VC node. Also, all internal loads
on the VC node are disabled so that the charge state of
the VC node will be saved on the internal compensation
capacitor. This feature reduces transient recovery time.
When the PWM input again transitions high, the demand
current for the switch returns to the value just before PWM
last transitioned low. To further reduce transient recovery
time, an external MOSFET should be used to disconnect
the LED array current loop when PWM is low, stopping
COUT from discharging.
3519fa
8
LT3519/LT3519-1/LT3519-2
APPLICATIONS INFORMATION
Dimming Control
There are two methods to control the current source for
dimming using the LT3519/LT3519-1/LT3519-2. The first
method, PWM Dimming, uses the PWM pin to modulate
the current source between zero and full current to achieve
a precisely programmed average current. To make this
method of current control more accurate, the switch demand current is stored on the internal VC node during the
quiescent phase when PWM is low. This feature minimizes
recovery time when the PWM signal goes high. To obtain
best PWM dimming performance, it is necessary to use
an external disconnect switch in the LED current path to
prevent the output capacitor from discharging during the
PWM signal low phase. For best product of analog and PWM
dimming, the minimum PWM low or high time should be at
least six switching cycles (3μs for fSW = 2MHz). Maximum
PWM period is determined by the system. The maximum
PWM dimming ratio (PWMRATIO) can be calculated from
the maximum PWM period (tMAX) and the minimum PWM
pulse width (tMIN) as follows:
PWMRATIO =
tMAX
tMIN
When VCTRL is higher than 1.2V, the LED current is clamped
to be:
ILED =
250mV
RSENSE
When VCTRL is more than 1V but less than 1.2V, the
LED current is in the nonlinear region of VISP-VISN
Threshold vs VCTRL as shown in the Typical Performance
Characteristics.
The LED current programming feature through the CTRL
pin possibly increases the total dimming range by a factor
of ten. In order to have the accurate LED current, precision
resistors are preferred (1% is recommended). The CTRL
pin should not be left open. Tie to VREF if not used.
Programming Output Voltage (Constant Voltage
Regulation) or Open LED/Overvoltage Threshold
For a boost application, the output voltage can be set by
selecting the values of R1 and R2 (see Figure 1) according
to the following equation:
⎛ R1 ⎞
VOUT = ⎜ +1⎟ • 1.22V
⎝ R2 ⎠
Example:
tMAX = 9ms, tMIN = 3μs (fSW = 2MHz)
PWMRATIO =
9ms
= 3000:1
3µs
The second method of dimming control, Analog Dimming, uses the CTRL pin to linearly adjust the current
sense threshold during the PWM high state. When the
CTRL pin voltage is less than 1V but more than 100mV,
the LED current is:
ILED =
VOUT
R1
LT3519/
LT3519-1/ FB
LT3519-2
R2
3519 F01
Figure 1. FB Resistor Divider for Boost LED Driver
VCTRL – 100mV
4 • RSENSE
3519fa
9
LT3519/LT3519-1/LT3519-2
APPLICATIONS INFORMATION
For open LED protection of a boost type LED driver, set
the resistor from the output to the FB pin such that the
expected VFB during normal operation will not exceed
1.1V. For a buck mode or buck-boost mode LED driver,
the output voltage is typically level-shifted to a signal with
respect to GND as illustrated in Figure 2. The open LED
voltage level can be expressed as:
VOUT = VBE(Q1) +
R1
• 1.22V
R2
+
R1 V
The falling SHDN/UVLO value can be accurately set by
the resistor divider. A small 2.2μA pull-down current is
active when SHDN/UVLO is below the 1.22V threshold.
The purpose of this current is to allow the user to program
the rising hysteresis. The following equations should be
used to determine the values of the resistors:
R1+ R2
• 1.22V
R2
VIN(RISING) = 2.2µA • R1+ VIN(FALLING)
VIN(FALLING) =
RSENSE(EXT)
OUT
–
LT3519/
LT3519-1/ FB
LT3519-2
Programming the Turn-On and Turn-Off Thresholds
with the SHDN/UVLO Pin
100k
VIN
LED
ARRAY
R1
Q1
LT3519/
LT3519-1/ SHDN/UVLO
LT3519-2
R2
R2
3519 F02
3519 F03
Figure 2. Open LED Protection FB Resistor Connector
for Buck Mode or Buck-Boost Mode LED Driver
Figure 3. SHDN/UVLO Threshold Programming
3519fa
10
LT3519/LT3519-1/LT3519-2
APPLICATIONS INFORMATION
Inductor Selection
The inductor used with the LT3519/LT3519-1/LT3519-2
should have a saturation current rating of 1A or greater.
For buck mode LED drivers, the inductor value should be
chosen to give a ripple current 150mA or more. In the
buck mode, the inductor value can be estimated using
the formula:
D
• ( VIN – VLED ) ⎛ µH • A • MHz ⎞
L (µH) = BUCK
⎜
⎟
fOSC (MHz) • 0.15A ⎝
V
⎠
V
DBUCK = LED
VIN
VLED is the voltage across the LED string, VIN is the input
voltage to the converter, and fOSC is the switching frequency.
In the boost configuration, the inductor can be estimated
using the formula:
L (µH) =
DBOOST • VIN ⎛ µH • A • MHz ⎞
⎜
⎟
fOSC (MHz) • 0.15A ⎝
V
⎠
DBOOST =
( VLED – VIN )
VLED
Table 1. Recommended Inductor Vendors
VENDOR
PHONE
WEB
Sumida
(408)321-9660
www.sumida.com
Toko
(408)432-8281
www.toko.com
Cooper
(561)998-4100
www.cooperet.com
Vishay
(402)563-6866
www.vishay.com
Input Capacitor Selection
For proper operation, it is necessary to place a bypass
capacitor to GND close to the VIN pin of the LT3519/
LT3519-1/LT3519-2. A 1μF or greater capacitor with low
ESR should be used. A ceramic capacitor is usually the
best choice.
In the buck mode configuration, the capacitor at the input
to the power converter has large pulsed currents. For
best reliability, this capacitor should have low ESR and
ESL and have an adequate ripple current rating. A 2.2μF
ceramic type capacitor is usually sufficient for LT3519
(400kHz version). A capacitor of proportionately less
value for LT3519-1/LT3519-2 (higher frequency version)
can be used.
Output Capacitor Selection
The selection of output capacitor depends on the load
and converter configuration, i.e., step-up or step-down
and the operating frequency. For LED applications, the
equivalent resistance of the LED is typically low, and the
output filter capacitor should be sized to attenuate the
current ripple.
To achieve the same LED ripple current, the required filter
capacitor value is larger in the boost and buck-boost mode
applications than that in the buck mode applications. Lower
operating frequencies will require proportionately higher
capacitor values. For LED buck mode applications, a 1μF
ceramic capacitor is usually sufficient. For the LED boost
and buck-boost mode applications, a 2.2μF ceramic capacitor is usually sufficient. Very high performance PWM
dimming applications may require a larger capacitor value
to support the LED voltage during PWM transitions.
Use only ceramic capacitors with X7R, X5R or better dielectric as they are best for temperature and DC bias stability
of the capacitor value. All ceramic capacitors exhibit loss
of capacitance value with increasing DC voltage bias, so
it may be necessary to choose a higher value capacitor
to get the required capacitance at the operation voltage.
Always check that the voltage rating of the capacitor is
sufficient.
Table 2. Recommended Ceramic Capacitor Vendors
VENDOR
PHONE
WEB
TDK
(516)535-2600
www.tdk.com
Kemet
(408)986-0424
www.kemet.com
Murata
(814)237-1431
www.murata.com
Taiyo Yuden
(408)573-4150
www.t-yuden.com
3519fa
11
LT3519/LT3519-1/LT3519-2
APPLICATIONS INFORMATION
Open LED Detection
Board Layout
The LT3519/LT3519-1/LT3519-2 provide an open-collector
status pin, OPENLED, that pulls low when the FB pin is
within ~60mV of its 1.22V regulated voltage. If the open
LED clamp voltage is programmed correctly using the FB
pin, then the FB pin should never exceed 1.1V when LEDs
are connected, therefore, the only way for the FB pin to
be within 60mV of the 1.22V regulation voltage is for an
open LED event to have occurred.
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
To prevent electromagnetic interference (EMI) problems,
proper layout of high frequency switching paths (see
Figure 4) is essential. Minimize the length and area of all
traces connected to the switching node pin (SW). Keep the
sense voltage pins (ISP and ISN) away from the switching
node. The bypass capacitor on the VIN supply to the LT3519
should be placed as close as possible to the VIN pin and
GND. Likewise, place COUT next to the CATHODE pin. Do
not extensively route high impedance signals such as FB
and CTRL, as they may pick up switching noise. Figure 5
shows the recommended component placement.
Inrush Current
The LT3519/LT3519-1/LT3519-2 have a built-in Schottky
diode for a boost converter. When supply voltage is applied to VIN pin, the voltage difference between VIN and
VOUT generates inrush current flowing from input through
the inductor and the Schottky diode to charge the output
capacitor. The selection of inductor and capacitor value
should ensure the peak of the inrush current to below
10A. In addition, the LT3519/LT3519-1/LT3519-2 turn-on
should be delayed until the inrush current is less than the
maximum current limit. If the peak of the inrush current
is more than 10A, an external Schottky diode should be
used to bypass both the inductor and internal Schottky.
The recommended Schottky diodes for hot plug are shown
on Table 3.
L1
+
VENDOR
Zetex
International Rectifier
PART NUMBER
VR (V)
IAVE (A)
DFLS160
60
1
ZLLS10000TA
40
1
10MQ060N
60
1.5
D1
VOUT
VIN
LOAD
3519 F04
Figure 4. High Frequency Path
GND
GND
VREF
OPENLED
PWM
CTRL
SHDN/UVLO
FB
VIN
ISN
ISP
SW
ANODE CATHODE
GND
GND
Table 3. Schottky Diodes Recommended for Hot Plug
Diodes, Inc
SW
RS
L1
COUT
CIN
VIN
GND
VOUT
3519 F05
Figure 5. Suggested Layout
3519fa
12
LT3519/LT3519-1/LT3519-2
TYPICAL APPLICATIONS
4W Boost Automotive LED Driver
VIN
6V TO 30V
L1
68μH
VOUT
C2
4.7μF
C1
1μF
SW ANODE CATHODE
VIN
ISP
RSENSE
2.49Ω
1M
SHDN/UVLO
100k
1M
243k
VREF
ISN
1M
LT3519
FB
CTRL
38V LED
100mA
29.4k
137k
OPENLED
GND
PWM
M1
C1: TDK C3216X7R1H105K
PWM
C2: MURATA GRM32ER71H475KA88
L1: COILTRONICS DR74-680-R
M1: VISHAY SILICONIX Si2308DS
RSENSE: STACKPOLE ELECTRONICS RHC 2512 2.49
5V
3519 TA02a
NOTE:
VIN = 8.2V RISING TURN ON
VIN = 6.2V FALLING UVLO
VIN > 10V FULL LED CURRENT AND FOLDBACK BELOW
VOUT 42.7V OVERVOLTAGE PROTECTION
1000:1 PWM Dimming at 120Hz
Efficiency vs VIN
94
PWM
5V/DIV
92
EFFICIENCY (%)
ILED
0.1A/DIV
IL
0.3A/DIV
VIN = 12V
2μs/DIV
90
88
3519 TA02b
86
84
6
10
14
18
VIN (V)
22
26
30
3519 TA02c
3519fa
13
LT3519/LT3519-1/LT3519-2
TYPICAL APPLICATIONS
Buck-Boost Mode 150mA LED Driver
16V LED 150mA
RSENSE
1.65Ω
VOUT
C2
1μF
L1
47μH
VIN
6V TO 24V
C1
1μF
1M
VIN
SW ANODE
SHDN/UVLO
100k
243k
1M
VREF
ISN
LT3519
PWM
ISP
CATHODE
357k
CTRL
C3
4.7μF
10k
210k
Q1
OPENLED
C1: TDK C3216X7R1H105K
C2: TDK C3216X7R1H105K
C3: TDK C3216X7R1E475K
L1: COILTRONICS DR73-470-R
Q1: DIODES FMMT555 PNP
FB
GND
24.3k
3519 TA03a
NOTE:
VIN = 8.2V RISING TURN ON
VIN = 6.2V FALLING UVLO
VIN > 7V FULL LED CURRENT AND FOLDBACK BELOW
VOUT – VIN 18.5V OVERVOLTAGE PROTECTION
Waveform for Open LED
Efficiency vs VIN
82
ILED
0.1A/DIV
80
EFFICIENCY (%)
78
VOUT
10V/DIV
OPENLED
10V/DIV
VIN = 12V
50μs/DIV
3519 TA03b
76
74
72
70
68
66
6
9
12
15
VIN (V)
18
21
24
3519 TA03c
3519fa
14
LT3519/LT3519-1/LT3519-2
TYPICAL APPLICATIONS
Buck Mode 500mA LED Driver
VIN
12V TO 30V
(UP TO 40V TRANSIENT)
C1
4.7μF
1M
1M SHDN
VIN CATHODE
ISP
SHDN/UVLO
RSENSE
0.5Ω
CTRL
100k
191k
LT3519
1.5k
ISN
VREF
130k
M1
OPENLED
C2
10μF
Q2
9V LED
500mA
C1: MURATA GRM32ER71H475KA88
C2: TDK C3216X7R1C106M
Q1: DIODES FMMT555 PNP
Q2: DIODES FMMT494 NPN
L1: COILTRONICS DR73-470-R
M1: VISHAY SILICONIX Si2337DS
1k
10k
VOUT
Q1
L1
47μH
SW
ANODE
GND
FB
PWM
14.7k
5V
PWM
3519 TA04a
2000:1 PWM Dimming at 120Hz
Efficiency vs VIN
90
PWM
5V/DIV
88
EFFICIENCY (%)
ILED
0.5A/DIV
IL
0.3A/DIV
VIN = 20V
1μs/DIV
86
84
3519 TA04b
82
80
12
15
18
21
VIN (V)
24
27
30
3519 TA04c
3519fa
15
LT3519/LT3519-1/LT3519-2
TYPICAL APPLICATIONS
Boost 150mA LED Driver
VIN
6V TO 20V
L1
15μH
C1
1μF
SW
ANODE
VIN
LT3519-1
1M
100k
VOUT
CATHODE
C2
2.2μF
ISP
SHDN/UVLO
RSENSE
1.65Ω
243k
ISN
VREF
1M
1M
CTRL
FB
137k
40k
24V LED
150mA
•
•
•
OPENLED
GND
PWM
PWM
C1: TDK C3216X7R1H105K
C2: MURATA GRM31CR71H225KA88
L1: COILTRONICS DR74-150-R
M1: VISHAY SILICONIX Si2318DS
RSENSE: STACKPOLE ELECTRONICS RHC 2512 2.49 AND 4.99
M1
5V
3519 TA05a
NOTE:
VIN = 8.2V RISING TURN-ON
VIN = 6.2V FALLING UVLO
VIN > 10V FULL LED CURRENT AND FOLDBACK BELOW
VOUT = 31.7V OVERVOLTAGE PROTECTION
3000:1 PWM Dimming at 120Hz
Efficiency vs VIN
94
PWM
5V/DIV
92
EFFICIENCY (%)
ILED
0.15A/DIV
IL
0.5A/DIV
VIN = 12V
0.5μs/DIV
90
88
86
3519 TA05b
84
82
6
8
10
12
14
VIN (V)
16
18
20
3519 TA05c
3519fa
16
LT3519/LT3519-1/LT3519-2
TYPICAL APPLICATIONS
Minimum BOM Buck Mode 500mA LED Driver
VIN
10V TO 25V
C1
2.2μF
VIN CATHODE
ISP
SHDN/UVLO
0.5Ω
LT3519-2
100k
130k
ISN
1M
C2
1μF
CTRL
6V LED
500mA
140k
VREF
10k
VOUT
PWM
Q1
L1
6.8μH
OPENLED
SW
ANODE
GND
FB
23.2k
C1:
C2:
Q1:
L1:
TDK C3216X7R1E225K
TDK C1608X7R1C105K
DIODES FMMT555 PNP
COILTRONICS DR73-068-R
3519 TA06a
Waveforms for Open LED
Efficiency vs VIN
84
ILED
0.5A/DIV
82
EFFICIENCY (%)
80
VIN – VOUT
5V/DIV
OPENLED
10V/DIV
78
76
74
VIN = 15V
25μs/DIV
3519 TA06b
72
70
10
13
16
19
VIN (V)
22
25
3519 TA06c
3519fa
17
LT3519/LT3519-1/LT3519-2
PACKAGE DESCRIPTION
MS Package
16-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1669 Rev Ø)
0.889 p 0.127
(.035 p .005)
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
0.305 p 0.038
(.0120 p .0015)
TYP
4.039 p 0.102
(.159 p .004)
(NOTE 3)
0.50
(.0197)
BSC
0.280 p 0.076
(.011 p .003)
REF
16151413121110 9
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
DETAIL “A”
3.00 p 0.102
(.118 p .004)
(NOTE 4)
4.90 p 0.152
(.193 p .006)
0o – 6o TYP
GAUGE PLANE
0.53 p 0.152
(.021 p .006)
DETAIL “A”
0.18
(.007)
SEATING
PLANE
1234567 8
1.10
(.043)
MAX
0.17 – 0.27
(.007 – .011)
TYP
0.50
(.0197)
BSC
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.86
(.034)
REF
0.1016 p 0.0508
(.004 p .002)
MSOP (MS16) 1107 REV Ø
3519fa
18
LT3519/LT3519-1/LT3519-2
REVISION HISTORY
REV
DATE
A
Nov 09
DESCRIPTION
PAGE NUMBER
Updated to Add LT3519-1 and LT3519-2 Parts
1-20
3519fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
19
LT3519/LT3519-1/LT3519-2
TYPICAL APPLICATIONS
SEPIC 150mA LED Driver
C3
2.2μF
L1A
68μH
VIN
4V TO 24V
•
C1
1μF
L1B
68μH
•
VOUT
SW ANODE CATHODE
ISP
VIN
C2
4.7μF
RSENSE
1.65Ω
1M
SHDN/UVLO
100k
1M
432k
VREF
ISN
1M
LT3519
FB
CTRL
16V LED
150mA
69.8k
158k
OPENLED
GND
PWM
C1: TDK C3216X7R1H105K
C2: TDK C3216X7R1E475K
C3: TDK C3216X7R1E225K
L1: COILTRONICS DRQ74-680-R (COUPLED INDUCTOR)
M1: VISHAY SILICONIX Si2318DS
NOTE:
VIN = 6V RISING TURN ON
VIN = 4V FALLING UVLO
VIN > 9V FULL LED CURRENT AND FOLDBACK BELOW
VOUT 18.5V OVERVOLTAGE PROTECTION
M1
PWM
5V
3519 TA07a
Efficiency vs VIN
Waveforms for LED Shorted to Ground
88
86
IL1A+IL1B
0.2A/DIV
EFFICIENCY (%)
84
ILED
0.1A/DIV
ILED_SHORTED
0.5A/DIV
82
80
78
VIN = 12V
3519 TA07b
50μs/DIV
76
74
4
8
12
16
20
24
VIN (V)
3519 TA07c
RELATED PARTS
PART NUMBER
LT1618
DESCRIPTION
Constant-Current, Constant-Voltage 1.24MHz, High
Efficiency Boost Regulator
LT3466/LT3466-1 Dual Full Function, 2MHz Diodes White LED Step-Up
Converter with Built-In Schottkys
LT3486
Dual 1.3A White LED Converter with 1000:1 True Color
PWM Dimming
LT3491
2.3MHz White LED Driver with Integrated Schottky Diode
COMMENTS
Up to 16 White LEDs, VIN: 1.6V to 18V, VOUT(MAX) = 34V, IQ= 1.8mA,
ISD < 1μA, MS Package
Up to 20 White LEDs, VIN: 2.7V to 24V, VOUT(MAX) = 39V, DFN/TSSOP-16
Packages
Drives Up to 16 100mA White LEDs. VIN: 2.5V to 24V, VOUT(MAX) = 36V,
DFN/TSSOP Packages
Drives Up to 6 LEDs. VIN: 2.5V to 12V, VOUT(MAX) = 27V, SC70/DFN
Packages
LT3497
Dual Full Function 2.3MHz LED Driver with 250:1 True
Color PWM Dimming with Integrated Schottky Diodes
LT3517
Full-Featured LED Driver with 1.5A Switch Current
LT3518
Full-Featured LED Driver with 2.3A Switch Current
Drives Up to 12 LEDs. VIN: 2.5V to 10V, VOUT(MAX) = 32V, 3mm × 2mm
DFN Package
VIN: 3V to 40V, VOUT(MAX) = 45V, Dimming = 5.000:1 True Color PWM,
ISD < 1μA, 4mm × 4mm QFN and TSSOP Packages
VIN: 3V to 40V, VOUT(MAX) = 45V, Dimming = 3.000:1 True Color PWM,
ISD < 1μA, 4mm × 4mm QFN and TSSOP Packages
LT3591
Constant-Current, 1MHz, High Efficiency White LED
Step-Up Converter with Built-in Schottkys
Up to 10 White LEDs, VIN: 2.5V to 12V, VOUT(MAX) = 45V, 3mm × 2mm DFN
Package
3519fa
20 Linear Technology Corporation
LT 1109 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2009