LT3598
1
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TYPICAL APPLICATION
FEATURES
APPLICATIONS
DESCRIPTION
6-String 30mA LED Driver
with ±1.5% Current Matching
The LT
®
3598 is a fi xed frequency step-up DC/DC converter
designed to drive up to six strings of LEDs at an output
voltage up to 44V. LED dimming can be achieved with
analog dimming on the CTRL pin, and with pulse width
modulation dimming on the PWM pin. The LT3598
accurately regulates LED current even when the input
voltage is higher than the LED output voltage. The switching
frequency is programmable from 200kHz to 2.5MHz
through an external resistor.
Additional features include programmable overvoltage
protection, switching frequency synchronization to an
external clock, LED current derating based on junction
temperature and/or LED temperature, LED string disable
control, OPENLED alert pin and output voltage limiting
when all LED strings are disconnected. The LT3598 is
available in a thermally enhanced 24-lead (4mm × 4mm)
QFN and 24-lead TSSOP packages.
90% Effi cient LED Driver for 60 White LEDs
n True Color PWM™ Dimming Delivers Up to 3000:1
Dimming Ratio
n Drives Six Strings of LEDs at Up to 30mA
n ±1.5% Accurate LED Current Matching
n Wide Input Voltage Range: 3.2V to 30V
n Output Voltage Up to 44V
n Regulates Current Even When VIN > VOUT
n Disconnects LEDs in Shutdown
n Programmable Open LED Protection (Regulated)
n OPENLED Alert Pin
n Programmable LED Current Derating
n Adjustable Frequency: 200kHz to 2.5MHz
n Synchronizable to an External Clock
n Parallel Channels for Higher Current per LED String
n Thermally Enhanced 4mm × 4mm QFN and 24-Lead
TSSOP Packages
n Notebook Computer Display
n Medium Size Displays
n Automotive LCD Display
LED Current Matching
2.61k
2.2μF
10μH
4.7μF
15nF
20mA
3598 TA01a
LT3598
VO_SW
FB
OPENLED
PWM
SHDN
RT
SYNC
CTRL
VREF
LED1
LED2
LED3
LED4
LED5
LED6
VOUT
SW
VIN
VC
SS GND
TSET ISET
1.00M
30.9k
PVIN
8V TO 40V
2.2μF
VIN
5V
14.7k
10nF
47pF
100k
100k
10k
51.1k
100k
60.4k
PWM
SHDN
SYNC
TEMPERATURE (°C)
–50
MATCHING (%)
0.5
1.0
0
–0.5
050
–25 25 75 100 125
–1.0
–1.5
1.5
3598 TA01b
ALL SIX LED STRINGS
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, 7321203.
LT3598
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PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS
SHDN ................................................................VIN + 3V
VIN, OPENLED ...........................................................30V
SW Voltage ...............................................................45V
VOUT, VO_SW Voltage .................................................44V
LED1 to LED6 ............................................................44V
PWM, SYNC, CTRL, RT, SS, VC ................................... 6V
(Note 1)
1
2
3
4
5
6
7
8
9
10
11
12
TOP VIEW
FE PACKAGE
24-LEAD PLASTIC TSSOP
24
23
22
21
20
19
18
17
16
15
14
13
SW
VOUT
VO_SW
LED1
LED2
LED3
LED4
LED5
LED6
OPENLED
ISET
CTRL
VIN
SHDN
GND
VREF
SS
RT
PWM
SYNC
NC
TSET
FB
VC
25
TJMAX = 125°C, θJA = 38°C/W
EXPOSED PAD (PIN 25) IS PGND, MUST BE SOLDERED TO PCB
24 23 22 21 20 19
25
7 8 9
TOP VIEW
UF PACKAGE
24-LEAD (4mm s 4mm) PLASTIC QFN
10 11 12
6
5
4
3
2
1
13
14
15
16
17
18
LED1
LED2
LED3
LED4
LED5
LED6
VREF
SS
RT
PWM
SYNC
NC
VO_SW
VOUT
SW
VIN
SHDN
GND
OPENLED
ISET
CTRL
VC
FB
TSET
TJMAX = 125°C, θJA = 37°C/W
EXPOSED PAD (PIN 25) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3598EUF#PBF LT3598EUF#TRPBF 3598 24-Lead (4mm × 4mm) Plastic QFN –40°C to 125°C
LT3598IUF#PBF LT3598IUF#TRPBF 3598 24-Lead (4mm × 4mm) Plastic QFN –40°C to 125°C
LT3598EFE#PBF LT3598EFE#TRPBF LT3598 24-Lead Plastic TSSOP –40°C to 125°C
LT3598IFE#PBF LT3598IFE#TRPBF LT3598 24-Lead Plastic TSSOP –40°C to 125°C
Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grade is identifi ed by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based fi nish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifi
cations, go to: http://www.linear.com/tapeandreel/
VREF, FB Voltage..........................................................6V
ISET, TSET .....................................................................6V
Operating Junction Temperature Range
(Note 2) ..................................................–40°C to 125°C
Maximum Junction Temperature........................... 125°C
Storage Temperature Range ...................–65°C to 150°C
LT3598
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ELECTRICAL CHARACTERISTICS
The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at TA = 25°C. VIN = 5V, VSHDN = VIN unless otherwise noted. (Note 2)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Operating Voltage 3 3.2 V
Maximum Operating Voltage 30 V
Reference Voltage
l
1.216
1.210 1.230 1.260
1.260 V
V
Reference Voltage Line Regulation 3.2V < VIN < 30V, VC = 0.3V 0.01 0.03 %/V
Maximum VREF Pin Current Out of Pin 200 μA
FB Pin Bias Current VFB = 1.230V (Note 3) 100 250 nA
FB Error Amp Transconductance ΔI = 5μA 300 μmhos
FB Error Amp Voltage Gain 600 V/V
FB Pin Voltage 1.22 1.24 1.26 V
Current Loop Amp Transconductance 21 μmhos
Current Loop Amp Voltage Gain 80 V/V
VC Sink Current 10 μA
Quiescent Current VSHDN = 5V, PWM = 0V, Not Switching 3.5 5 mA
Quiescent Current in Shutdown VSHDN = 0V 0 1 μA
ISET Voltage VCTRL = 1.5V, VTSET = 1.5V, RISET = 14.7kΩ 0.985 1.000 1.015 V
LED Current RISET = 14.7kΩ 19.5 20 20.7 mA
LED String Current Matching 20mA LED Current l±0.5 ±1.5 %
LED Open Detection Threshold 0.2 0.25 V
OPENLED Sink Current 2mA
Minimum LED Regulation Voltage 0.8 V
LED1-6 Leakage Current VLED1-6 = 1V, VOUT = 5V, PWM = 0V
VLED1-6 = 42V, VOUT = 44V, PWM = 0V 0.1
0.2 1
2μA
μA
CTRL Pin Bias Current VCTRL = 0.8V (Note 4) 50 125 nA
Switching Frequency RT = 309kΩ
RT = 51.1kΩ
RT = 14.7kΩ
171
0.9
2.25
190
1
2.5
209
1.1
2.75
kHz
MHz
MHz
TSET Voltage 602 mV
Maximum Switch Duty Cycle RT = 309kΩ
RT = 51.1kΩ
RT = 14.7kΩ
l
90
87
80
95
90
86
%
%
%
Switch Current Limit (Note 5) 1.5 2 2.5 A
Switch VCESAT ISW = 0.5A 0.12 V
Switch Leakage Current VSW = 40V 0.2 5 μA
LT3598
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PARAMETER CONDITIONS MIN TYP MAX UNITS
SHDN Pin Current VSHDN = 0V
VSHDN = 5V 0.1
30 1
60 μA
μA
SHDN Voltage High 1.6 V
SHDN Voltage Low 0.4 V
Soft-Start Charging Current VSS = 0.1V 5 10 15 μA
PWM Input High Voltage 1V
PWM Input Low Voltage 0.4 V
PWM Pin Bias Current PWM = 3.3V 0.1 1 μA
SYNC Input High Voltage 1.5 V
SYNC Input Low Voltage 0.4 V
SYNC Pin Bias Current SYNC = 0V
SYNC = 3.3V 25
0.1 50
1μA
μA
VO_SW Switch Resistance 1000 Ω
ELECTRICAL CHARACTERISTICS
The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at TA = 25°C. VIN = 5V, VSHDN = VIN unless otherwise noted. (Note 2)
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 LT3598E is guaranteed to meet performance specifi cations
from 0°C to 125°C junction temperature. Specifi cations over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LT3598I is guaranteed over the full –40°C to 125°C operating junction
temperature range.
Note 3: Current fl ows out of FB pin.
Note 4: Current fl ows out of CTRL pin.
Note 5: Current limit guaranteed by design and/or correlation to static test.
Current limit is independent of duty cycle and is guaranteed by design.
LT3598
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TYPICAL PERFORMANCE CHARACTERISTICS
SHDN Pin Turn-On Threshold SHDN Pin Current Quiescent Current
Reference Voltage Oscillator Frequency Switch Current Limit
Switch VCESAT Soft-Start Pin Current Feedback Pin Voltage
TEMPERATURE (°C)
–50
SHDN THRESHOLD (V)
1.4
1.3
050
–25 25 75 100 125
1.2
1.5
3598 G01
VSHDN (V)
0
0
SHDN PIN CURRENT (μA)
5
15
20
25
50
35
10 20 25
10
40
45
30
515 30 35
3598 G02
125°C
–50°C 25°C
TEMPERATURE (°C)
–50
QUIESCENT CURRENT (mA)
5
4
050
–25 25 75 100 125
3
2
6
3598 G03
TEMPERATURE (°C)
–50
REFERENCE VOLTAGE (V)
1.230
1.235
1.225
1.220
050
–25 25 75 100 125
1.215
1.240
3598 G04
VIN = 40V
VIN = 30V
VIN = 5V
TEMPERATURE (°C)
–50
OSCILLATOR FREQUENCY (MHz)
2.0
2.5
1.5
1.0
050
–25 25 75 100 125
0.5
0
3.0
3598 G05
2.5MHz
1MHz
200kHz
TEMPERATURE (°C)
–50
SWITCH CURRENT (A)
2.0
2.4
1.6
1.2
050
–25 25 75 100 125
0.8
0.4
2.8
3598 G06
TEMPERATURE (°C)
–50
ISS (μA)
12.5
10.0
050
–25 25 75 100 125
7.5
5.0
15.0
3598 G08
TEMPERATURE (°C)
–50
FEEDBACK VOLTAGE (V)
1.23
1.22
050
–25 25 75 100 125
1.21
1.20
1.24
3598 G09
VC = 1.5V
VC = 1V
SWITCH CURRENT (A)
0
VCESAT (V)
0.30
0.35
0.40
0.25
0.20
0.25 0.750.50 1.00 1.25 1.5O
0.05
0
0.15
0.10
3598 G07
125°C
–50°C
25°C
LT3598
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TYPICAL PERFORMANCE CHARACTERISTICS
LED Current vs PWM Duty Cycle LED Current vs Temperature LED Current vs CTRL Voltage
LED Current Matching
vs Temperature OPENLED Sink Current
LED Current Waveforms
(0.1% PWM)
LED Current Waveforms
(90% PWM)
LED Current Waveforms
(0.1% PWM)
LED Current Waveforms
(90% PWM)
PWM DUTY CYCLE (%)
0.01
0.001
LED CURRENT (mA)
1
100
1100.1 100
3598 G10
0.1
0.01
10
TEMPERATURE (°C)
–50
LED CURRENT (mA)
20.1
20.2
20.0
19.9
050
–25 25 75 100 125
19.8
19.7
20.3
3598 G11
CTRL VOLTAGE (V)
0
LED CURRENT (mA)
15
20
25
1.0
10
5
00.2 0.4 0.6 0.8 1.2
3598 G12
TEMPERATURE (°C)
–50
MATCHING (%)
0.5
1.0
0.0
–0.5
050
–25 25 75 100 125
–1.0
–1.5
1.5
3598 G13
TEMPERATURE (°C)
–50
OPENLED CURRENT (mA)
2.0
2.5
1.5
1.0
050
–25 25 75 100 125
0.5
0
3.0
3598 G14
20μs/DIV
PWM
5V/DIV
SW
20V/DIV
ILED1
50mA/DIV
IL
1A/DIV
3598 G15
2μs/DIV
PWM
5V/DIV
SW
20V/DIV
ILED1
50mA/DIV
IL
1A/DIV
3598 G16 100μs/DIV
PWM
5V/DIV
SW
20V/DIV
ILED1
50mA/DIV
IL
1A/DIV
3598 G17 5μs/DIV
PWM
5V/DIV
SW
20V/DIV
ILED1
50mA/DIV
IL
1A/DIV
3598 G18
LT3598
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PIN FUNCTIONS
LED1-6 (Pins 1, 2, 3, 4, 5, 6/Pins 4, 5, 6, 7, 8, 9): LED
String Output. Connect the bottom cathode of each LED string
to these pins. Tie pins to VOUT if the string is not used.
OPENLED (Pin 7/Pin 10): Open LED Flag When Any LED
String Opens. The output is open-collector. Tie a resistor
to other supply for open LED fl ag function.
ISET (Pin 8/Pin 11): Programs LED Current for Each String.
Connect a 14.7k resistor between ISET and GND to program
each LED string current to 20mA. A 47pF capacitor on the
ISET pin reduces current ripple in each LED string.
CTRL (Pin 9/Pin 12): LED Current Control. If the CTRL
pin is not used, tie this pin to VREF through a 10k to 20k
resistor.
VC (Pin 10/Pin 13): Error Amplifi er Output Pin. Tie the
external compensation network to this pin.
FB (Pin 11/Pin 14): Feedback Pin for Overvoltage
Protection. Reference voltage is 1.230V. Connect the
resistive divider tap here. Minimize trace area at FB. Set VOUT
according to VOUT = 1.230(1 + R2/R1) when overvoltage
protection occurs (see Figure 2).
TSET (Pin 12/Pin 15): An external resistor divider from
VREF programs a decrease in LED current versus internal
junction temperature (setting temperature breakpoint and
slope). If the TSET pin is not used, tie this pin to VREF.
NC (Pin 13/Pin 16): No Connection.
SYNC (Pin 14/Pin 17): Frequency Synchronization Pin.
This input allows for synchronizing the operating frequency
to an external clock. The RT resistor should be chosen to
program a switching frequency 20% slower than SYNC
pulse frequency. This pin should be grounded if this
feature is not used.
PWM (Pin 15/Pin 18): Input Pin for PWM Dimming Control.
Above 1V allows converter switching and below 0.4V
disables switching with VC pin level maintained. A PWM
signal driving the PWM pin provides accurate dimming
control. The PWM signal can be driven from 0V to 5V. If
unused, the pin should be connected to VREF.
RT (Pin 16/Pin 19): A resistor to ground programs
switching frequency between 200kHz and 2.5MHz. For
SYNC function, choose the resistor to program a frequency
20% slower than the SYNC pulse frequency. Do not leave
this pin open.
SS (Pin 17/Pin 20): Soft-Start Pin. Place a soft-start
capacitor here. Upon start-up, a 10μA current charges
the capacitor. Use a larger capacitor for slower start-up.
Leave open if not used.
VREF (Pin 18/Pin 21): Bandgap Voltage Reference.
Internally set to 1.230V. This pin can supply up to 100μA.
Can be used to program the CTRL pin voltage using resistor
dividers to ground.
GND (Pin 19/Pin 22): Ground. Tie directly to local ground
plane.
SHDN (Pin 20/Pin 23): Shutdown Pin. Tie to 1.6V or more
to enable the device. Tie below 0.4V or less to disable
device. Do not fl oat this pin.
VIN (Pin 21/Pin 24): Input Supply Pin. Must be locally
bypassed with a capacitor to ground.
SW (Pin 22/Pin 1): Switch Pin. This is the collector of the
internal NPN power switch. Minimize the metal trace area
connected to this pin to minimize EMI.
VOUT (Pin 23/ Pin 2): Output Pin. This pin provides power
to all LEDs.
VO_SW (Pin 24/ Pin 3): Drain of an Internal PMOS. The
internal PMOS disconnects the feedback resistors from
the VOUT pin during shutdown and the PWM transitioned
to low.
Exposed Pad (Pin 25/ Pin 25): Ground. The Exposed Pad
must be soldered to the PCB.
(QFN/ TSSOP)
LT3598
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BLOCK DIAGRAM
3598 F01
TSET
CTRL
VREF
PWM
Q1
–
+
–
+
–
+
OPENLED DETECTION OPENLED
LED1
LED2
LED3
LED4
LED5
LED6
R
VO_SW
VOUT
LED
DISABLE
DETECTION
FB
GND
GND
ISET
SS
SWSYNCRT
VIN
SHDN
–
+
LED gm
0.8V
OVP gm
A3
A1
VC
–
+
VOUT
PWM DIMMING
LOGIC
SLOPE
OSCILLATOR
1.230VREF
3SQ
A2
VPTAT
LED
DRIVE
CIRCUITRY
Figure 1. Block Diagram
LT3598
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OPERATION
The LT3598 uses a constant-frequency, peak current mode
control scheme to provide excellent line and load regulation.
Each string can drive up to 30mA with 1.5% matching ac-
curacy between strings. Operation can be best understood
by referring to the Block Diagram in Figure 1.
LT3598 has a built-in boost converter which converts the
input voltage to a higher output voltage to drive LEDs.
The LED strings are connected to current sources where
the current level is set with an external resistor on the
ISET pin. The LED1 to LED6 voltages are monitored for
output voltage regulation. During normal operation, when
all LEDs are used, the lowest LED pin voltage (LED1 to
LED6) is used to regulate the output voltage to ensure all
LED strings have enough voltage to run the programmed
current.
For any unused LED strings, tie their LED pins to VOUT.
An unused LED string is no longer in the regulation loop,
nor does it affect open LED detection. Never allow unused
LED strings to be left open.
The basic loop uses a pulse from an internal oscillator
to set the SR latch and turn on the internal power NPN
switch Q1. The signal at the noninverting input of the PWM
comparator (A2 slope) is proportional to the sum of the
switch current and oscillator ramp. When slope exceeds
VC (the output of the gm amplifi er), the PWM comparator
resets the latch. The switch is then turned off, causing the
inductor current to lift the SW pin and turn on an external
Schottky diode connected to the output. Inductor current
fl ows via the Schottky diode charging the output capaci-
tor. The switch is turned on again at the next reset cycle
of the internal oscillator. During normal operation, the VC
voltage controls the peak switch current limit and, hence,
the inductor current available to the output LEDs.
Dimming of the LEDs is accomplished by pulsing the LED
current using the PWM pin. When the PWM pin is low,
switching is disabled and the error amplifi er is turned off
so that it does not drive the VC pin. Also, all internal loads
on the VC pin are disabled so that the state of the VC pin
is maintained on the external compensation capacitor.
This feature reduces transient recovery time. When the
PWM input again transitions high, the peak switch current
returns to the correct value.
The LT3598 uses the FB pin to provide overvoltage protec-
tion when all LED strings are open. There is an internal
PMOS switch between VOUT and VO_SW that is controlled
by the PWM signal. During the PWM off-period, this
PMOS is turned off, allowing for higher dimming range
and lower current during shutdown. A resistor divider is
connected between the VO_SW pin and ground, which sets
the overvoltage protection voltage.
If the LED1-6 pin voltage is below 0.2V (for a certain delay
after 80% of the programmed output voltage is reached),
the string is treated as an open LED string. As a result,
OPENLED fl ag is set. If a LED string is open in the middle
of the operation, the regulation will continue.
OPENLED detection is disabled during the start-up phase
to avoid erratic fl ag generation. An LED string that is
disabled by connecting its LED pin to VOUT is not an open
LED condition. During normal operation, if an LED string
is open and has the lowest LED pin voltage, the output
voltage will regulate itself to fi nd another LED string that has
the lowest LED pin voltage at about 0.8V. If the open LED
string has an LED voltage above 0.8V, the output voltage
will remain the same. When the LED string is open, it is
no longer in the regulation loop. The OPENLED detection
is active only when the PWM signal is enabled. To avoid
spurious OPENLED detection and high PWM dimming
ratio, more output capacitance is recommended to allow
less voltage drop on VOUT.
During start-up, 10μA of current charges the external
soft-start capacitor. The SS pin directly limits the rate of
voltage rise on the VC pin, which in turn, limits the peak
switch current. Soft-start also enables the switching
frequency foldback to provide a clean start-up for the
LT3598. Current limit protects the power switch and
external components.
LT3598
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Inductor Selection
Table 1 lists several inductors that work well with the
LT3598, however, there are many other manufacturers and
devices that can be used. Consult each manufacturer for
detailed information on their entire range of parts. Ferrite
core inductors should be used to obtain the best effi ciency.
Choose an inductor that can handle the necessary peak
current without saturating. Also, ensure that the inductor
has a low DCR (copper wire resistance) to minimize I2R
power losses. Values between 4.7μH and 22μH will suffi ce
for most applications.
Inductor manufacturers specify the maximum current
rating as the current where inductance falls by a given
percentage of its nominal value. An inductor can pass a
current greater than its rated value without damaging it.
Consult each manufacturer to determine how the maximum
inductor current is measured and how much more current
the inductor can reliably conduct.
Table 1. Recommended Inductors
PART
L
(μH)
MAX
DCR
(Ω)
CURRENT
RATING
(A) VENDOR
B1015AS-100M
#817FY-4R7M
1123AS-4R7M
10
4.7
4.7
0.07
0.06
0.12
2.2
2.26
1.90
TOKO
www.toko.com
74454068
74454010
7447745100
6.8
10
10
0.055
0.065
0.12
2.2
2
1.7
Würth Electronics
www.we-online.com
CDH74NP-120L
CDH74NP-150L
CDRH6D38-100
12
15
10
0.065
0.083
0.038
2.45
2.10
2.00
Sumida
www.sumida.com
IHLP-2525BD-01 10 0.129 2.5 Vishay
www.vishay.com
SD25-4R7-R 4.7 0.056 1.83 Cooper
www.cooperet.com
LPS4018-472ML 4.7 0.200 1.8 Coilcraft
www.coilcraft.com
Capacitor Selection
Low ESR (equivalent series resistance) ceramic capacitors
should be used at the output to minimize the output
ripple voltage. Use only X5R or X7R dielectrics, as these
materials retain their capacitance over wider voltage and
APPLICATIONS INFORMATION
temperature ranges than other dielectrics. A 4.7μF to 10μF
output capacitor is suffi cient for most high output current
designs. Table 2 lists some suggested manufacturers.
Consult the manufacturers for detailed information on
their entire selection of ceramic parts.
Table 2. Recommended Ceramic Capacitor Manufacturers
Taiyo Yuden 408-573-4150
www.t-yuden.com
AVX 843-448-9411
www.avxcorp.com
Murata 770-436-1300
www.murata.com
Kemet 408-986-0424
www.kemet.com
United Chemi-Con 847-696-2000
www.chemi-con.com
Diode Selection
Schottky diodes, with their low forward voltage drop
and fast switching speed, must be used for all LT3598
applications. Do not use P-N diodes. Table 3 lists several
Schottky diodes that work well. The diode’s average current
rating must exceed the application’s average output current.
The diode’s maximum reverse voltage must exceed the
application’s output voltage. A 2A diode is suffi cient for
most designs. For PWM dimming applications, be aware
of the reverse leakage current of the diode. Lower leakage
current will drain the output capacitor less, allowing for
higher dimming range. The companies below offer Schottky
diodes with high voltage and current ratings.
Table 3. Suggested Diodes
PART
MAX
CURRENT
(A)
MAX REVERSE
VOLTAGE
(V) MANUFACTURER
B250A
B240A
SBR140S3
SBM340, PDS340
2
2
1
3
50
40
40
40
Diodes, Inc.
www.diodes.com
HSM150G
HSM150J
1
1
50
50
Microsemi
www.microsemi.com
SS3H9 3 90 Vishay
www.vishay.com
LT3598
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Overvoltage Protection
The LT3598 uses the FB pin to provide regulated overvoltage
protection when all LED strings are open. A resistor divider
is connected between the VO_SW pin and ground (Figure 2).
There is an internal PMOS switch between VOUT and
VO_SW, which is controlled by the PWM signal. The PMOS
switch addition prevents the feedback resistor divider from
draining the output capacitor during PWM off-period,
allowing for a higher dimming range without falsely tripping
the OPENLED fl ag. It also reduces the system current in
shutdown. This PMOS has about 1k resistance, so select
FB resistors taking this resistance into account.
To set the maximum output voltage, select the values
of R1 and R2 (see Figure 2) according to the following
equation:
VV
R
R
OUT MAX().=+
⎛
⎝
⎜⎞
⎠
⎟
1 230 1 2
1
APPLICATIONS INFORMATION
Figure 2. Overvoltage Protection
Voltage Feedback Connections
The output voltage should be set 15% higher than the
normal LED string operating voltage. Under normal
operation, LED1 to LED6 pin voltages are monitored and
provide feedback information to the converter for output
voltage regulation given the programmed LED current.
The maximum output regulation loop is activated only
when all LEDs are open.
Programming Maximum LED Current
Maximum LED current is programmed by placing a resistor
between the ISET pin and ground (RISET). The ISET pin
resistor can be selected from 10k to 100k.
The LED current is programmed according to the following
equation:
IV
R
LED ISET
≈294
See Table 4 and Figure 3 for resistor values and corr-
esponding programmed LED current.
LED current can also be adjusted by programming the
CTRL pin voltage.
Table 4. RISET Value Selection for LED Current
LED CURRENT (mA) RESISTOR ON ISET PIN (k)
3mA 97.6
10mA 29.4
20mA 14.7
30mA 9.76
LED Current Dimming
Two different types of dimming control can be used with
the LT3598. The LED current can be set by modulating
the CTRL pin or the PWM pin.
For some applications, a variable DC voltage that adjusts
the LED current is the preferred method of brightness
control. The CTRL pin voltage can be modulated to set
the dimming of the LED string (see Figures 4 and 5). As
the voltage on the CTRL pin increases from 0V to 1.0V,
the LED current increases from 0 to the programmed LED
current level. As the CTRL pin voltage increases beyond
1V, it has no effect on the LED current.
Figure 3. RISET Value Selection for LED Current
3598 F02
LT3598
VO_SW
FB
VOUT
R2
R1
RISET (k)
0
LED CURRENT (mA)
20
25
15
10
40 80
20 60 100
5
0
30
3598 F03
LT3598
12
3598fb
APPLICATIONS INFORMATION
For True Color PWM
TM
dimming, the LT3598 provides up
to a 3000:1 PWM dimming range. This is achieved by
allowing the duty cycle of the PWM pin (connected to
the IC and an internal switch in series with the LED(s)),
to be reduced from 100% to as low as 0.1% for a PWM
frequency of 100Hz (Figure 6). PWM duty cycle dimming
allows for constant LED color to be maintained over the
entire dimming range.
For wide PWM dimming range, higher switching freq-
uency and lower PWM frequency confi guration are
needed. Special considerations are required for component
selection and compensation network. Please contact
factory for optimized components selection if very high
dimming ratio is desired.
LED Current Derating Using the CTRL Pin
A useful feature of the LT3598 is its ability to program
a derating curve for maximum LED current versus
temperature. LED data sheets provide curves of maximum-
allowable LED current versus temperature to warn against
exceeding this current limit and damaging the LED. The
LT3598 allows the output LEDs to be programmed for
maximum allowable current while still protecting the
LEDs from excessive currents at high temperature. This
is achieved by programming a voltage at the CTRL pin
with a negative temperature coeffi cient using a resistor
divider with temperature dependent resistance (Figure 7).
As ambient temperature increases, the CTRL voltage will
fall below the internal 1V voltage reference, causing LED
currents to be controlled by the CTRL pin voltage. The LED
current curve breakpoint and slope versus temperature
is defi ned by the choice of resistor ratios and use of
temperature-dependent resistance in the divider for the
CTRL pin.
Table 5 shows a list of manufacturers/distributors of
NTC resistors. There are several other manufacturers
available and the chosen supplier should be contacted
for more detailed information. If an NTC resistor is used
to indicate LED temperature, it is effective only if the
resistor is connected as closely as possible to the LED
strings. LED derating curves shown by manufacturers are
listed for ambient temperature. The NTC resistor should
have the same ambient temperature as the LEDs. Since
the temperature dependency of an NTC resistor can be
nonlinear over a wide range of temperatures, it is important
to obtain a resistor’s exact value over temperature from
the manufacturer. Hand calculations of CTRL voltage can
then be performed at each given temperature, resulting
in the CTRL versus temperature plotted curve. Several
iterations of resistor value calculations may be required
to achieve the desired breakpoint and slope of the LED
current derating curve.
Figure 4. LED Current vs CTRL Voltage
Figure 5. LED Current vs CTRL
Figure 6. LED Current Using PWM Dimming
3598 F05
LT3598
VREF
CTRL
R2
R1
PWM
INDUCTOR
CURRENT
3598 F06
LED
CURRENT
MAX ILED
TPWM
TONPWM (= 1/fPWM)
CTRL (V)
0
LED CURRENT (mA)
20
25
30
1.4
15
10
0.4 0.8
0.2 0.6 1 1.2 1.6
5
0
35
3598 F04
RISET = 9.76k
LT3598
13
3598fb
Table 5. NTC Resistor Manufacturers/Distributors
Murata Electronics North America 770-436-1300
www.murata.com
TDK Corporation 516-535-2600
www.tdk.com
Digi-Key 800-344-4539
www.digikey.com
If calculating the CTRL voltage at various temperatures
gives a downward slope that is too strong, alternative
resistor networks can be chosen (B, C, D in Figure 7)
which use temperature independent resistance to reduce
the effects of the NTC resistor overtemperature.
Murata Electronics provides a selection of NTC resistors
with complete data over a wide range of temperatures.
In addition, a software tool is available which allows the
user to select from different resistor networks and NTC
resistor values, and then simulate the exact output voltage
curve (CTRL behavior) overtemperature. Referred to as the
“Murata Chip NTC Thermistor Output Voltage Simulator,”
users can log onto www.murata.com and download
the software followed by instructions for creating an
output voltage VOUT (CTRL) from a specifi ed VCC supply
(VREF).
Using the TSET Pin for Thermal Protection
The LT3598 contains a special programmable thermal
regulation loop that limits the internal junction temperature
of the part. Since the LT3598 topology consists of a single
boost converter with six linear current sources, any LED
string voltage mismatch will cause additional power to
be dissipated in the package. This topology provides
excellent current matching between LED strings and allows
a single power stage to drive a large number of LEDs, but
at the price of additional power dissipation inside the part
APPLICATIONS INFORMATION
(which means a higher junction temperature). Being able
to limit the maximum junction temperature allows the
benefi ts of this topology to be fully realized. This thermal
regulation feature provides important protection at high
ambient temperatures, and allows a given application
to be optimized for typical, not worst-case, ambient
temperatures with the assurance that the LT3598 will
automatically protect itself and the LED strings under
worst-case conditions.
The operation of the thermal loop is simple. As the ambient
temperature increases, so does the internal junction
temperature of the part. An internal voltage is developed
that’s proportional to the junction temperature (VPTAT).
Once the programmed maximum junction temperature
is reached, the LT3598 begins to linearly reduce the LED
current, as needed, to try and maintain this temperature.
This can only be achieved when the ambient temperature
stays below the desired maximum junction temperature.
If the ambient temperature continues to rise past the
programmed maximum junction temperature, the LEDs
current will be reduced to approximately 5% of the full
LED current.
While this feature is intended to directly protect the LT3598,
it can also be used to derate the LED current at high
temperatures. Since there is a direct relationship between
the LED temperature and LT3598 junction temperature, the
TSET function also provides some LED current derating
at high temperatures.
Two external resistors program the maximum IC junction
temperature using a resistor divider from the VREF pin,
as shown in Figure 8. Choose the ratio of R1 and R2 for
the desired junction temperature. Figure 9 shows the
relationship of TSET voltage to junction temperature, and
Table 6 shows commonly used values for R1 and R2.
Figure 7 . LED Current Derating vs Temperature Using NTC Resistor
3598 F07
RY
RY
RXRX
RNTC RNTC RNTC RNTC
DCBA
LT3598
VREF
CTRL
R2
R1
(OPTION A TO D)
LT3598
14
3598fb
APPLICATIONS INFORMATION
Table 6. TSET Junction Temperature
TJ (°C) R1 R2
90 100k 68.1k
100 100k 63.4k
110 100k 59k
120 100k 54.9k
Programming Switching Frequency
The switching frequency of the LT3598 should be
programmed between 200kHz and 2.5MHz by an external
resistor connected between the RT pin and ground. Do not
leave this pin open. See Table 7 and Figure 10 for resistor
values and corresponding frequencies.
Selecting the optimum switching frequency depends
on several factors. Inductor size is reduced with higher
frequency, but effi ciency drops slightly due to higher
switching losses. In addition, some applications require
very high duty cycles to drive a large number of LEDs from
a low supply. Low switching frequency allows a greater
operational duty cycle and, hence, a greater number of
LEDs to be driven. In each case, the switching frequency
can be tailored to provide the optimum solution. When
programming the switching frequency, the total power
losses within the IC should be considered.
Table 7. Switching Frequency
SWITCHING FREQUENCY (MHz) RT (k)
2.5 14.7
2 20.5
1.5 29.4
1 51.1
0.5 105
0.2 301
Switching Frequency Synchronization
The nominal operating frequency of the LT3598 is
programmed using a resistor from the RT pin to ground
and can be controlled over a 200kHz to 2.5MHz range. In
addition, the internal oscillator can be synchronized to an
external clock applied to the SYNC pin. The synchronizing
clock signal input to the LT3598 must have a frequency
between 250kHz and 3MHz, a duty cycle between 20% and
80%, a low state below 0.4V and a high state above 1.5V.
Synchronization signals outside of these parameters will
cause erratic switching behavior. For proper operation,
an RT resistor should be chosen to program a switching
frequency 20% slower than the SYNC pulse frequency.
Synchronization occurs at a fi xed delay after the rising
edge of SYNC.
Figure 8. Programming the TSET Pin
Figure 9. TSET Pin Threshold
3598 F08
LT3598
VREF
TSET
R2
R1
JUNCTION TEMPERATURE (°C)
0
500
VTSET THRESHOLD (mV)
600
700
800
50 100 125
25 75 150
900
550
650
750
850
3598 F09
Figure 10. Switching Frequency
RT (k)
SWITCHING FREQUENCY (MHz)
2.5
2.0
1.5
0
1.0
0.5
1000
10 100
3598 F10
LT3598
15
3598fb
The SYNC pin should be grounded if the clock sync-
hronization feature is not used. When the SYNC pin is
grounded, the internal oscillator generates switching
frequency to the converter.
Soft-Start and Switching Frequency Foldback
For many applications, it is necessary to minimize the
inrush current at start-up. The LT3598’s soft-start circuit
signifi cantly reduces the start-up current spike and output
voltage overshoot. Before the SS pin voltage reaches 1V,
the switching frequency will also fold back proportional
to the SS pin voltage. A typical value for the soft-start
capacitor is 10nF.
OPENLED FLAG
The OPENLED pin is an open-collector output and needs
an external resistor tied to a supply (see Figure 11). If any
LED string is open during normal operation, the OPENLED
pin will be pulled down.
Loop Compensation
The LT3598 has an internal transconductance error
amplifi er for LED current regulation whose VC output
compensates the control loop. During an open LED
event where all LED strings are open, the VC node also
compensates the control loop. The external inductor,
output capacitor, and the compensation resistor and
capacitor determine the loop stability. The inductor and
output capacitor are chosen based on performance, size
and cost. The compensation resistor and capacitor at VC
are selected to optimize control loop stability. For typical
LED applications, a 15nF compensation capacitor in series
with a 3k resistor at VC is adequate.
Thermal Considerations
The LT3598 provides six channels for LED strings with
internal NPN devices serving as constant-current sources.
When LED strings are regulated, the lowest LED pin voltage
is typically 0.8V. The higher the programmed LED current,
the more power dissipation in the LT3598. For 30mA LED
programming current with a 100% PWM dimming ratio,
at least 144mW is dissipated within the IC due to current
sources. If the forward voltages of the six LED strings are
very dissimilar, there can be signifi cant power dissipation.
Thermal calculations shall include the power dissipation
on current sources in addition to conventional switch DC
loss, switch AC loss and input quiescent loss. For best
effi ciency, it is recommended that all channels have the
same number of LEDs, and each string has a similar voltage
drop across the LEDs.
Board Layout Considerations
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 is essential.
Minimize the length and area of all traces connected to the
switching node pin (SW). Always use a ground plane under
the switching regulator to minimize interplane coupling.
Good grounding is essential in LED fault detection.
APPLICATIONS INFORMATION
Figure 11. OPENLED Connection
3598 F11
LT3598
OPENLED
R1
The OPENLED fl ag is only activated after the fi rst PWM
edge. The open LED detection is enabled only when the
PWM signal is enabled. There is a delay for OPENLED
fl ag generation when the PWM signal is enabled to avoid
generating a spurious fl ag signal. The maximum current
the OPENLED can sink is typically 2mA.
During start-up (see the Operation section), the open LED
detection is disabled. If an LED string is not used and tied
to VOUT, the string will not be in any fault detection.
LT3598
16
3598fb
TYPICAL APPLICATIONS
L1
10μH D1
C2
4.7μF
3598 TA02a
LT3598
VO_SW
FB
OPENLED
PWM
SHDN
SYNC
LED1
LED2
LED3
LED4
LED5
LED6
VOUT
SWVIN
R4
1.00M
R5
30.9k
R3
14.7k
R7
100k
C1: TAIYO YUDEN GMK325BJ225ML
C2: MURATA GRM32ER71H475K
C3: TAIYO YUDEN LMK212BJ225MG
D1: DIODES, INC. B240A
L1: WÜRTH ELEKTRONIK 744777410
RNTC: MURATA NCP18WF104J03RB
RNTC
100k
RHOT
10k
R6
100k
PWM
SHDN
SYNC
C1
2.2μF
PVIN
6V TO 40V
C3
2.2μF
VIN
5V
RC
2.61k
CC
15nF
RT
CTRL
VREF
VC
SS GND
TSET ISET
C4
0.1μF
C5
47pF
R1
51.1k
R8
60.4k
20mA
LED Driver for 40 White LEDs with Two Channels Unused
Effi ciency (PWM Dimming)
TOTAL LED CURRENT (mA)
0
EFFICIENCY (%)
80
85
90
70
75
70
20 40
10 90
30 50 80
60
60
50
65
55
95
3598 TA02b
PVIN = 25V
PVIN = 12V
LT3598
17
3598fb
TYPICAL APPLICATIONS
LED Driver for 30 White LEDs with 60mA Each String
L1
10μH D1
C2
4.7μF
3598 TA03a
LT3598
VO_SW
FB
OPENLED
PWM
SHDN
SYNC
LED1
LED2
LED3
LED4
LED5
LED6
VOUT
SWVIN
R4
1.00M
R5
30.9k
PWM
SHDN
SYNC
CTRL
CTRL
R6
100k
C1
2.2μF
PVIN
6V TO 40V
C3
2.2μF
VIN
5V
R3
9.76k
R7
100k
C1: TAIYO YUDEN GMK325BJ225ML
C2: MURATA GRM32ER71H475KA88L
C3: TAIYO YUDEN LMK212BJ225MG
D1: VISHAY SS3H9
L1: WÜRTH ELEKTRONIK 744777410
RNTC: MURATA NCP18WF104J03RB
RHOT
10k
RT
CTRL
VREF
VC
SS GND
TSET ISET
C4
0.1μF
C5
47pF
R1
51.1k
60mA
RNTC
100k
RC
2.61k
CC
15nF
R8
60.4k
Effi ciency (PWM Dimming)
Dimming Range (1000:1 PWM) at 125°C
Junction Temperature, 10ms Period
TOTAL LED CURRENT (mA)
0
EFFICIENCY (%)
80
85
90
140
75
70
40 80
20 180
60 100 160
120
65
60
100
95
3598 TA03b
PVIN = 25V
PVIN = 12V
2μs/DIV
PWM
5V/DIV
SW
20V/DIV
ILED1
100mA/DIV
359
8
LT3598
18
3598fb
TYPICAL APPLICATIONS
Auto Battery Powered Driver for 20 LEDs with 90mA Each String
Effi ciency
L1
4.7μH
C2
4.7μF
3598 TA04a
LT3598
VO_SW
FB
OPENLED
RT
LED1
LED2
LED3
LED4
LED5
LED6
VOUT
SWVIN
R10
20k CTRL
VREF
PWM
SHDN
SYNC
PWM
SHDN
CTRL
CTRL
100k
PVIN
6V TO 40V
C3
2.2μF
VIN
5V
D1
R4
1.00M
R5
30.9k
C1
2.2μF
R3
9.76k
C1: NIPPON CHEMI-CON KTS500B225M32NOTOO
C2: MURATA GRM32ER71H475KA88L
C3: TAIYO YUDEN LMK212BJ225MG
D1: VISHAY SS3H9
L1: WÜRTH ELEKTRONIK 7447785004
VC
SS GND
TSET ISET
C4
0.1μF
C5
56pF
R1
51.1k
90mA
R7
100k
RC
5.11k
CC
6.8nF
R8
60.4k
Dimming Range 1000:1 PWM,
10ms Period (125°C Junction Temperature)
TOTAL LED CURRENT (mA)
0
EFFICIENCY (%)
80
85
90
140
75
70
40 80
20 180
60 100 160
120
65
60
95
3598 TA04b
5μs/DIV
PWM
5V/DIV
ILED1
100mA/DIV
3598 TA04c
LT3598
19
3598fb
TYPICAL APPLICATIONS
L1
10μH D1
C2
4.7μF
3598 TA02a
LT3598
VO_SW
FB
OPENLED
PWM
SHDN
SYNC
LED1
LED2
LED3
LED4
LED5
LED6
VOUT
SWVIN
R4
2.4M
R5
140k
R3
14.7k
R7
178k
C1: MURATA GRM21BR71E225K
C2: MURATA GRM32ER71H475K
C3: TAIYO YUDEN LMK212BJ225MG
D1: DIODES, INC. SBR140S3
L1: TOKO 1123AS-100M
R9
10k
R6
100k
PWM
SHDN
SYNC
C1
2.2μF
PVIN
11.4V TO 12.6V
C3
2.2μF
VIN
3.2V TO 5.5V
RC
2k
CC
10nF
RT
CTRL
VREF
VC
SS GND
TSET ISET
C4
0.1μF
C5
47pF
R1
21.5k
R8
107k
20mA
C6
100pF
2 MHz LED Driver for 20 White LEDs
PWM Dimming (3000:1)
PWM
5V/DIV
IL
200mA/DIV
ILED, total
50mA/DIV
3598 TA07a
PVIN = 12V, VIN = 3.3V
1μs/DIV
LT3598
20
3598fb
PWM
5V/DIV
IL
500mA/DIV
ILED, total
50mA/DIV
3598 TA06
PVIN = VIN = 5V
5μs/DIV
TYPICAL APPLICATIONS
1 MHz LED Driver for 36 White LEDs
PWM Dimming (20μS Pulse Width)
L1
10μH D1
C2
4.7μF s 2
3598 TA07
LT3598
VO_SW
FB
OPENLED
PWM
SHDN
SYNC
LED1
LED2
LED3
LED4
LED5
LED6
VOUT
SWVIN
R4
2.4M
R5
76.8k
R3
11.5k
C1: MURATA GRM21BR71A225K
C2: MURATA GRM32ER71H475K
D1: DIODES, INC. SBR140S3
L1: VISHAY IHLP-2525BD-01
R9
10k
R6
100k
PWM
SHDN
SYNC
C1
2.2μF
VIN
5V
C3
1μF
RC
3k
CC
10nF
RT
CTRL
VREF
VC
SS GND
TSET ISET
C4
0.1μF
C5
47pF C6
100pF
R1
53.6k
R8
107k
25mA
LT3598
21
3598fb
PACKAGE DESCRIPTION
FE24 (AA) TSSOP 0208 REV Ø
0.09 – 0.20
(.0035 – .0079)
0o – 8o
0.25
REF
RECOMMENDED SOLDER PAD LAYOUT
0.50 – 0.75
(.020 – .030)
4.30 – 4.50*
(.169 – .177)
134
5678 9 10 11 12
14 13
7.70 – 7.90*
(.303 – .311)
3.25
(.128)
2.74
(.108)
2021222324 19 18 17 16 15
1.20
(.047)
MAX
0.05 – 0.15
(.002 – .006)
0.65
(.0256)
BSC 0.195 – 0.30
(.0077 – .0118)
TYP
2
2.74
(.108)
0.45 p0.05
0.65 BSC
4.50 p0.10
6.60 p0.10
1.05 p0.10
3.25
(.128)
MILLIMETERS
(INCHES) *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.150mm (.006") PER SIDE
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
2. DIMENSIONS ARE IN
3. DRAWING NOT TO SCALE
SEE NOTE 4
4. RECOMMENDED MINIMUM PCB METAL SIZE
FOR EXPOSED PAD ATTACHMENT
6.40
(.252)
BSC
FE Package
24-Lead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1771 Rev Ø)
Exposed Pad Variation AA
LT3598
22
3598fb
PACKAGE DESCRIPTION
4.00 ± 0.10
(4 SIDES)
NOTE:
1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGGD-X)—TO BE APPROVED
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE, IF PRESENT
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
PIN 1
TOP MARK
(NOTE 6)
0.40 ± 0.10
2423
1
2
BOTTOM VIEW—EXPOSED PAD
2.45 ± 0.10
(4-SIDES)
0.75 ± 0.05 R = 0.115
TYP
0.25 ± 0.05
0.50 BSC
0.200 REF
0.00 – 0.05
(UF24) QFN 0105
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
0.70 ±0.05
0.25 ±0.05
0.50 BSC
2.45 ± 0.05
(4 SIDES)
3.10 ± 0.05
4.50 ± 0.05
PACKAGE OUTLINE
PIN 1 NOTCH
R = 0.20 TYP OR
0.35 × 45° CHAMFER
UF Package
24-Lead Plastic QFN (4mm × 4mm)
(Reference LTC DWG # 05-08-1697)
LT3598
23
3598fb
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
B 7/10 Updated data sheet title and 3rd bullet under Features to ±1.5%
Changed VIN condition in Reference Voltage Line Regulation to 3.2V
Deleted VIN = 5V conditions from SHDN Pin Current
Revised voltage in PWM description in Pin Functions
Fixed minor typo
Added “15%” to fi rst sentence of third paragraph
Added information to Using TSET Pin for Thermal Protection section
Changed to 250kHz in Switching Frequency Synchronization section
1
3
4
7
9
11
13
14
(Revision history begins at Rev B)
LT3598
24
3598fb
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2008
LT 0710 REV B • PRINTED IN USA
L1, 10μH D1
C2
4.7μF
3598 TA04a
LT3598
VO_SW
FB
OPENLED
PWM
SHDN
SYNC
LED1
LED2
LED3
LED4
LED5
LED6
VOUT
SWVIN
PWM
SHDN
SYNC
100k
PVIN
8V TO 40V
C3
2.2μF
VIN
5V
20mA
R4
1.00M
R5
30.9k
R3
14.7k
R7
100k
RHOT
10k
C1
2.2μF
RT
CTRL
VREF
VC
SS GND
TSET ISET
C5
47pF
R1
51.1k
C4
10nF
RNTC
100k
RC
2.61k
CC
15nF
R8
60.4k
RELATED PARTS
TYPICAL APPLICATION
PART NUMBER DESCRIPTION COMMENTS
LT3474/
LT3474-1 36V, 1A (ILED), 2MHz, Step-Down LED Driver VIN: 4V to 36V, VOUT(MAX) = 13.5V, True Color PWM Dimming = 400:1,
ISD < 1μA, TSSOP-16E Package
LT3475/
LT3475-1 Dual 1.5A (ILED), 36V, 2MHz, Step-Down LED Driver VIN: 4V to 36V, VOUT(MAX) = 13.5V, True Color PWM Dimming = 3000:1,
ISD < 1μA, TSSOP-20E Package
LT3476 Quad Output 1.5A, 2MHz High Current LED Driver with
1000:1 Dimming VIN: 2.8V to 16V, VOUT(MAX) = 36V, True Color PWM Dimming = 1000:1,
ISD < 10μA, 5mm × 7mm QFN-10 Package
LT3477 3A, 42V, 3MHz Boost, Buck-Boost, Buck LED Driver VIN: 2.5V to 25V, VOUT(MAX) = 40V, Dimming = Analog/PWM, ISD < 1μA,
QFN and TSSOP20E Packages
LT3478/LT3478-1 4.5A, 42V, 2.5MHz High Current LED Driver with 3000:1
Dimming VIN: 2.8V to 36V, VOUT(MAX) = 42V, True Color PWM Dimming = 3000:1,
ISD < 3μA, TSSOP16E Package
LT3486 Dual 1.3A, 2MHz High Current LED Driver VIN: 2.5V to 24V, VOUT(MAX) = 36V, True Color PWM Dimming = 1000:1,
ISD < 1μA, 5mm × 3mm DFN and TSSOP-16E Packages
LT3496 45V, 2.1MHz 3-Channel (ILED = 1A) Full Featured
LED Driver VIN: 3V to 30V (40VMAX), VOUT(MAX) = 45V, True Color PWM Dimming =
3000:1, ISD < 1μA, 4mm × 3mm QFN-28 Package
LT3497 Dual 2.3MHz, Full Function LED Driver with Integrated
Schottkys and 250:1 True Color PWM Dimming VIN: 2.5V to 10V, VOUT(MAX) = 32V, IQ = 6mA, ISD < 12μA, 2mm × 3mm
DFN-10 Package
LT3498 2.3MHz, 20mA LED Driver and OLED Driver with
Integrated Schottky VIN: 2.5V to 12V, VOUT(MAX) = 32V, IQ = 1.65mA, ISD < 9μA, 2mm × 3mm
DFN-10 Package
LT3518/LT3517 2.3A/1.3A 45V, 2.5MHz Full Featured LED Driver with
True Color PWM Dimming VIN: 3V to 30V (40VMAX), VOUT(MAX) = 42V, True Color PWM Dimming =
3000:1, ISD < 5μA, 4mm × 4mm QFN-16 Package
LT3590 48V, 850kHz 50mA Buck Mode LED Driver VIN: 4.5V to 55V, Dimming = 200:1 True Color PWM, ISD < 15μA,
2mm × 2mm DFN-6 and SC70 Packages
LT3592 36V, 2.2MHz, 500mA Buck Mode LED Driver VIN: 3.6V to 36V, True Color PWM Dimming = 10:1, ISD < 1μA, 2mm × 3mm
DFN-10 and MSOP-10E Packages
LT3595 45V, 2.5MHz 16-Channel Full Featured LED Driver VIN: 4.5V to 55V, VOUT(MAX) = 45V, True Color PWM Dimming = 5000:1,
ISD < 1μA, 5mm × 9mm QFN-56 Package
90% Effi cient LED Driver for 60 White LEDs Effi ciency vs Total LED Current
TOTAL LED CURRENT (mA)
0
60
EFFICIENCY (%)
70
80
90
20 40 8060 100
100
65
75
85
95
120
3598 TA05b
VIN = 25V
VIN = 16V
