LT3597
60V Triple Step-Down
LED Driver
Description
Features
Three 100mA Buck Regulators, Each Drives Up to
10 LEDs with Fast NPN Current Sources
n Fast Current Sources for 3
2.2
1-3
4.7
>3
3.3
1-3
15
>3
6.8
Table 1. Recommended Inductors
500
L (µH)
DCR (Ω)
CURRENT
RATING (A)
LPS6225
MSS1038
MSS1038
MSS1038
100
100
220
470
0.61
0.3
0.76
1.24
0.52
1.46
0.99
0.70
Coilcraft
www.coilcraft.com
CDRH105R
CDRW105R
CDRH105R
CDR6D28MN
100
220
470
100
0.253
0.50
1.29
0.9
1.35
0.94
0.60
0.75
Sumida
www.sumida.com
DS1262C2
DS1262C2
DS1262C2
100
220
470
0.17
0.35
1.243
1.5
1.0
0.7
Toko
www.toko.com
SLF10145T
SLF10145T
100
220
0.26
0.47
1.0
0.7
TDK
www.tdk.com
DR73
DR73
100
220
0.527
1.05
0.79
0.53
Coiltronics
www.cooperet.com
PART
VENDOR
Capacitor Selection
Low ESR (equivalent series resistance) capacitors should
be used at the outputs to minimize output ripple voltage.
Use only X5R or X7R dielectrics, as these materials retain
their capacitance over wider voltage and temperature
ranges than other dielectrics. Table 2 lists some suggested
manufacturers. Consult the manufacturers for detailed
information on their entire selection of ceramic surface
mount parts.
200
Diode Selection
Schottky diodes, with their low forward voltage drop and
fast switching speed, must be used for all LT3597 applications. Do not use P-N junction diodes. The diode’s
average current rating must exceed the application’s average current. The diode’s maximum reverse voltage must
exceed the application’s input voltage. Table 4 lists some
recommended Schottky diodes.
Table 4. Recommended Diodes
PART
MAX CURRENT MAX REVERSE
(A)
VOLTAGE (V)
MANUFACTURER
DFLS160
B160
1
1
60
60
Diodes, Inc.
www.diodes.com
CMMSH1-60
1
60
Central
www.centralsemi.com
ESIPB
1
100
Vishay
www.vishay.com
Table 2. Recommended Ceramic Capacitor Manufacturers
Taiyo Yuden
www.t-yuden.com
AVX
www.avxcorp.com
Murata
www.murata.com
Kemet
www.kemet.com
TDK
www.tdk.com
3597fa
11
LT3597
applications information
Undervoltage Lockout (UVLO)
Programming Maximum LED Current
The EN/UVLO can be used to program the input UVLO
threshold by connecting it to a resistor divider from the
VIN pin as shown in Figure 2.
Maximum LED current can be programmed by placing a
resistor (RISET1-3) between the ISET1-3 pin and ground.
RISET1-3 values between 20k and 100k can be chosen to
set the maximum LED current between 100mA and 20mA
respectively.
LT3597
VIN
R2
EN/UVLO
R1
1.51V
+
–
3597 F02
Figure 2. EN/UVLO Control
Select R1 and R2 according to the following equation:
The LED current is programmed according to the following equation:
1V
ILED1-3 = 2 •
(mA)
R
ISET1-3
See Table 5 and Figure 3 for resistor values and corresponding programmed LED current.
Table 5. LED Current Programming
RISET1-3 VALUE (kΩ)
LED CURRENT (mA)
20
100
R2
VIN(UVLO) = 1.51V • 1+
R1
In UVLO an internal 5.1µA pull-down current source is connected to the pin for programmable UVLO hysteresis. The
hysteresis can be set according to the following equation:
VUVLO(HYST) = 5.1µA • R2
Once the EN/UVLO pin falls below 0.4V, the part enters
into shutdown.
80
60
50
40
100
20
100
80
LED CURRENT (mA)
Care must be taken if too much hysteresis is programmed,
the pin voltage might drop too far and cause the current
source to saturate.
25
33.3
60
40
20
0
0
25
50
RSET1-3 (kΩ)
75
100
3597 F03
Figure 3. RISET1-3 Value for LED Current
3597fa
12
LT3597
Applications Information
LED Current Dimming
Two different types of dimming control are available with
the LT3597. The LED current can be dimmed using the
CTRL1-3 pin or the PWM1-3 pin.
For some applications, a variable DC voltage that adjusts
the LED current is the preferred method for brightness
control. In that case, the CTRL1-3 pin can be modulated
to set the LED dimming (see Figure 4). As the CTRL1-3 pin
voltage rises from 0V to 1.0V, the LED current increases
from 0mA to the maximum programmed LED current in a
linear fashion. As the CTRL1-3 pin continues to increase
past 1.0V, the maximum programmed LED current is
maintained. If this type of dimming control is not desired,
the CTRL1-3 pin can be tied to VREF .
120
LED CURRENT (mA)
100
80
60
40
20
0
0
0.25
0.5
0.75
1
CTRL1-3 (V)
1.25
1.5
3597 F04
Figure 4. LED Current vs CTRL1-3 Voltage
For True Color PWM dimming, the LT3597 provides up to
10,000:1 PWM dimming range at 100Hz. This is achieved
by allowing the duty cycle of the PWM1-3 pin to be reduced
from 100% to 0.01% for a PWM frequency of 100Hz (see
Figure 5), hence a minimum on-time of 1µs and a maximum period of 100ms. PWM duty cycle dimming allows
for constant LED color to be maintained over the entire
dimming range.
Using the TSET Pin for Thermal Protection
The LT3597 contains a special programmable thermal
regulation loop that limits the internal junction temperature. This thermal regulation feature provides important
protection at high ambient temperatures, and allows a
given application to be optimized for typical, not worstcase, ambient temperatures with the assurance that the
LT3597 will automatically protect itself and the LED strings
under worst-case conditions.
As the ambient temperature increases, so does the internal
junction temperature of the part. Once the programmed
maximum junction temperature is reached, the LT3597
linearly reduces the LED current, as needed, to maintain
this junction temperature. This can only be achieved when
the ambient temperature stays below the maximum programmed junction temperature. If the ambient temperature
continues to rise above the programmed maximum junction temperature, the LED current will reduce to less than
20% of the full current.
A resistor divider from the VREF pin programs the maximum
part junction temperature as shown in Figure 6.
tPWM
tON(PWM)
LT3597
PWM1-3
LED1-3
CURRENT
VREF
MAX ILED
R2
TSET
3597 F06
Figure 5. LED Current Using PWM Dimming
R1
3597 F07
Figure 6. Programming the TSET Pin
3597fa
13
LT3597
applications information
Table 6 shows commonly used values for R1 and R2.
Choose the ratio of R1 and R2 for the desired junction
temperature limit as described in Figure 7.
Table 6. TSET Programmed Junction Temperature
TJ (°C)
R1 (kΩ)
R2 (kΩ)
85
49.9
97.6
100
49.9
90.9
115
49.9
84.5
The TSET pin must be tied to VREF if the temperature protection feature is not desired.
0.8
TSET VOLTAGE (V)
0.7
0.6
0.5
LED Current Derating Using the CTRLM Pin
Another feature of the LT3597 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
LT3597 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 CTRLM pin
with a negative temperature coefficient using a resistor
divider with temperature dependent resistance (Figure 8).
As ambient temperature increases, the CTRLM voltage
will fall below the internal 1V voltage reference, causing
LED currents to be controlled by the CTRLM pin voltage.
The LED current curve breakpoint and slope versus temperature are defined by the choice of resistor ratios and
use of temperature-dependent resistance in the divider
for the CTRLM pin.
0.4
0.3
–50
–25
75
0
25
50
TEMPERATURE (°C)
100
125
3597 F07
Figure 7. TSET Voltage for Temperature Derating
LT3597
VREF
RY
RY
R2
R1
(OPTION
A TO D)
CTRLM
RNTC
RNTC
A
B
RX
C
RX
RNTC
RNTC
D
3597 F08
Figure 8. Programming the CTRLM Pin
3597fa
14
LT3597
Applications Information
Table 7 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 placed 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 the CTRLM voltage can
then be performed at each given temperature, resulting in
the CTRLM versus temperature plotted curve. Iterations of
resistor value calculations may be necessary to achieve the
desired break point and slope of the LED current derating
curve. From the CTRLM voltage, the LED current can be
found using the curve shown in Figure 9.
Table 7. NTC Resistor Manufacturers/Distributors
Murata
www.murata.com
TDK Corporation
www.tdk.com
Digi-Key
www.digikey.com
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 (CTRLM behavior) over temperature. 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 (CTRLM) from a specified VCC
supply (VREF).
The CTRLM pin must be tied to VREF if the temperature
derating function is not desired.
Programming Switching Frequency
The switching frequency of the LT3597 can be programmed
between 200kHz and 1MHz by an external resistor connected between the RT pin and ground. Do not leave this
pin open. See Table 8 and Figure 10 for resistor values
and corresponding frequencies.
Table 8. RT Resistor Selection
SWITCHING FREQUENCY (MHz)
RT VALUE (kΩ)
1.0
33.2
If calculating the CTRLM voltage at various temperatures
gives a downward slope that is too strong, use alternative
resistor networks (B, C, D in Figure 8). They use temperature independent resistance to reduce the effects of the
NTC resistor over temperature.
100
1.0
SWITCHING FREQUENCY (MHz)
1.2
LED CURRENT (mA)
120
80
60
40
20
0
0
0.25
0.5
0.75
1
CTRLM (V)
1.25
1.5
3597 F09
Figure 9. LED Current vs CTRLM Voltage
0.5
80
0.2
220
0.8
0.6
0.4
0.2
0
25
50
75
100 125 150 175 200 225
RT (kΩ)
3597 F10
Figure 10. Programming Switching Frequency
3597fa
15
LT3597
applications information
Selecting the optimum switching frequency depends
on several factors. Inductor size is reduced with higher
frequency, but efficiency drops slightly due to higher
switching losses. Some applications require very low
duty cycles to drive a small number of LEDs from a high
supply. Low switching frequency allows a greater range
of operational duty cycle and hence a lower number of
LEDs can 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.
Switching Frequency Synchronization
The nominal operating frequency of the LT3597 is programmed using a resistor from the RT pin to ground
over a 200kHz to 1MHz 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 LT3597 must have a frequency between 240kHz and
1MHz, a duty cycle between 20% and 80%, a low state
below 0.4V and a high state above 1.6V. Synchronization
signals outside of these parameters will cause erratic
switching behavior. For proper operation, an RT resistor
is chosen to program a switching frequency 20% slower
than the SYNC pulse frequency. Synchronization occurs
at a fixed delay after the rising edge of SYNC.
The SYNC pin must be grounded if the clock synchronization feature is not used. When the SYNC pin is grounded,
the internal oscillator controls the switching frequency of
the converter.
Operating Frequency Trade-offs
Selection of the operating frequency is a trade-off between
efficiency, component size, output voltage and maximum
input voltage. The advantage of high frequency operation
is smaller component sizes and values. The disadvantages
are lower efficiency and lower input voltage range for a
desired output voltage. The highest acceptable switching frequency (fSW(MAX)) for a given application can be
calculated as follows:
fSW(MAX) =
VD + VOUT
tON(MIN) ( VD + VIN − VSW )
where VIN is the typical input voltage, VOUT is the output
voltage, VD is the catch diode drop (0.5V) and VSW is the
internal switch drop (0.5V at max load). This equation
shows that slower switching is necessary to accommodate
high VIN /VOUT ratios. The reason the input voltage range
depends on the switching frequency is due to the finite
minimum switch on and off times. The switch minimum
on and off times are 200ns.
Adaptive Loop Control
The LT3597 uses an adaptive control mechanism to set
the buck output voltage. This control scheme ensures
maximum efficiency while not compromising minimum
PWM pulse widths. When PWM1-3 is low, the output of
the respective buck rises to a maximum value set by an
external resistor divider to the respective FB pin. Once
PWM1-3 goes high, the output voltage is adaptively reduced until the voltage across the LED current sink is 1V.
Figure 11 shows how the maximum output voltage can
be set by an external resistor divider.
LT3597
VOUT1-3
VOUT1-3
R2
FB1-3
R1
3597 F11
Figure 11. Programming Maximum VOUT1-3
The maximum output voltage must be set to exceed the
maximum LED drop plus 1V by a margin greater than 10%.
However, this margin must not exceed a voltage of 10V.
This ensures proper adaptive loop control. The equations
below are used to estimate the resistor divider ratio. The
sum of the resistors should be less than 100k to avoid
noise coupling to the FB pin.
(
)
R2
VOUT(MAX) = 1.1 VLED(MAX) + 1.1V = 1.2V • 1+
R1
VOUT(MAX) = VLED(MAX) +1.1V +VMARGIN
VMARGIN ≤ 10V
3597fa
16
LT3597
applications information
Minimum Input Voltage
The minimum input voltage required to generate an output
voltage is limited by the maximum duty cycle and the
output voltage (VOUT) set by the FB resistor divider. The
duty cycle is:
VD + VOUT
DC =
VIN − VCESAT + VD
where VD is the Schottky forward drop and VCESAT is the
saturation voltage of the internal switch. The minimum
input voltage is:
VD + VOUT(MAX)
VIN(MIN) =
+ VCESAT − VD
DCMAX
where VOUT(MAX) is calculated from the equation in the
Adaptive Loop Control section, and DCMAX is the minimum
rating of the maximum duty cycle.
Fault Flag
The FAULT pin is an open-collector output and needs an
external resistor tied to a supply. If the LED1-3 pin voltage exceeds 12V or if the LED1-3 pin voltage is within
1.25V of VOUT1-3 pins while PWM1-3 is high, the FAULT
pin will be pulled low. The FAULT pin will also be pulled
low if the internal junction temperature exceeds the TSET
programmed temperature limit.
There is an approximate 3µs delay for FAULT flag generation
when the PWM1-3 signal is enabled to avoid generating
a spurious flag signal. The maximum current the FAULT
can sink is typically 200µA.
Thermal Considerations
The LT3597 provides three 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 1V. More power dissipation occurs in the
LT3597 at higher programmed LED currents. For 100mA
of LED current with a 100% PWM dimming ratio, at least
300mW is dissipated within the IC due to current sources.
Thermal calculations must include the power dissipation
in the current sources in addition to conventional switch
DC loss, switch transient loss and input quiescent loss.
In addition, the die temperature of the LT3597 must be
lower than the maximum rating of 125°C. This is generally
not a concern unless the ambient temperature is above
100°C. Care should be taken in the board layout to ensure
good heat sinking of the LT3597. The maximum load
current should be derated as the ambient temperature approaches 125°C. The die temperature rise above ambient
is calculated by multiplying the LT3597 power dissipation
by the thermal resistance from junction to ambient. Power
dissipation within the LT3597 is estimated by calculating
the total power loss from an efficiency measurement and
subtracting the losses of the catch diode and the inductor.
Thermal resistance depends on the layout of the circuit
board, but 32°C/W is typical for the 5mm × 8mm QFN
package.
Board Layout
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.
Proper grounding is also essential for the external resistors
and resistor dividers that set critical operation parameters.
Both the LT3597 exposed pad and pin 18 are ground.
Resistors connected between ground and the CTRL1-3,
CTRLM, FB1-3, TSET, ISET1-3, RT and EN/UVLO pins are
best tied to pin 18 and not the ground plane.
3597fa
17
LT3597
Typical Applications
48V 1MHz Triple Step-Down 100mA RGB LED Driver
VIN
48V
10µF
VIN
270k
BOOST2
0.1µF 100µH
EN/UVLO
SW2
BOOST1
DA2
SW1
FB2
DA1
VOUT2
LED2
BOOST3
91k
VOUT1
R
2.2µF
100µH
97k
0.1µF
97k
4.7k
B
3.3µF
9.1k
VCC
5V
VOUT2
FB1
LT3597
0.1µF 100µH
VOUT1
LED1
BIAS
10µF
2.2µF
33.2k
(1MHz)
3.83k
FB3
FAULT
PWM1-3
CTRL1-3
SYNC
RT
3
97k
DA3
100k
3
VOUT3
SW3
ISET1
VOUT3
LED3
VREF
ISET2
ISET3
GND
TSET
CTRLM
3597 TA02
20k
20k
10k
20k
82.5k
G
VREF
49.9k
100k
Efficiency
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0
10 20 30 40 50 60 70 80 90 100
LED CURRENT PER CHANNEL (mA)
3597 TA02b
3597fa
18
LT3597
Typical applications
48V 1MHz Triple Step-Down 10W 100mA White LED Driver (3.6V LEDs)
VIN
48V
10µF
VIN
270k
BOOST2
0.1µF 100µH
EN/UVLO
SW2
BOOST1
DA2
SW1
FB2
DA1
VOUT2
LED2
BOOST3
91k
VOUT1
97k
2.2µF
100µH
0.1µF
97k
3.24k
2.2µF
3.24k
FB1
LT3597
VOUT1
LED1
BIAS
10µF
3
VOUT3
2.2µF
3.24k
FB3
33.2k
ISET1
VOUT3
LED3
VREF
ISET2
ISET3
20k
10k
TSET
GND CTRLM
3597 TA03
20k
97k
DA3
FAULT
PWM1-3
CTRL1-3
SYNC
RT
3
0.1µF 100µH
SW3
100k
20k
82.5k
VREF
49.9k
100k
Efficiency
90
80
70
EFFICIENCY (%)
VCC
5V
VOUT2
60
50
40
30
20
10
0
0
10 20 30 40 50 60 70 80 90 100
LED CURRENT PER CHANNEL (mA)
3597 TA03b
3597fa
19
LT3597
Typical Applications
24V 200kHz Triple Step-Down 100mA RGB LED Driver
VIN
24V
VIN
10µF
BOOST2
EN/UVLO
SW2
BOOST1
DA2
SW1
FB2
DA1
VOUT2
LED2
BOOST3
0.22µF
470µH
VOUT2
15µF
VOUT1
470µH
97k
R
0.22µF
97k
9.1k
G
15µF
9.1k
FB1
LT3597
VOUT1
LED1
BIAS
10µF
15µF
97k
9.1k
FB3
220k
VOUT3
DA3
FAULT
PWM1-3
CTRL1-3
SYNC
RT
3
470µH
SW3
100k
3
0.22µF
ISET1
VOUT3
LED3
VREF
ISET2
ISET3
GND
B
VREF
TSET
CTRLM
3597 TA04
20k
20k
20k
Efficiency
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0
10 20 30 40 50 60 70 80 90 100
LED CURRENT PER CHANNEL (mA)
3597 TA04b
3597fa
20
LT3597
Typical applications
48V 1MHz Triple Step-Down 20mA RGB LED Driver
VIN
48V
10µF
VIN
270k
BOOST2
0.1µF 100µH
EN/UVLO
SW2
BOOST1
DA2
SW1
FB2
DA1
VOUT2
LED2
BOOST3
91k
VOUT1
R
2.2µF
100µH
97k
0.1µF
97k
4.7k
B
3.3µF
9.1k
VCC
5V
VOUT2
FB1
LT3597
0.1µF 100µH
VOUT1
LED1
BIAS
10µF
2.2µF
33.2k
3.83k
FB3
FAULT
PWM1-3
CTRL1-3
SYNC
RT
3
97k
DA3
100k
3
VOUT3
SW3
ISET1
VOUT3
LED3
VREF
ISET2
ISET3
GND
TSET
CTRLM
3597 TA05
100k
100k
100k
10k
82.5k
G
VREF
49.9k
100k
3597fa
21
LT3597
Package Description
UHG Package
Variation: UHG52 (39)
52-Lead Plastic QFN (5mm × 8mm)
(Reference LTC DWG # 05-08-1846 Rev B)
43
41
39
6.40 REF
35 34 33 32 31 30 29 28
37
27
0.70 ± 0.05
44
26
25
24
46
5.50 ± 0.05
4.10 ± 0.05
23
48
22 3.20 REF
21
2.90 ±0.05
50
20
5.90 ±0.05
51
19
18
PACKAGE
OUTLINE
2
4
6
0.80 BSC
7
9
11 12
13 14 15 16
0.40 BSC
17
0.20 ± 0.05
7.10 ± 0.05
8.50 ± 0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
51 50
48
46
44
R = 0.10
TYP
0.75 ± 0.05
5.00 ± 0.10
0.00 – 0.05
46
48
PIN 1 NOTCH
R = 0.30 TYP OR
0.35 × 45° CHAMFER
50 51
0.40 ±0.10
PIN 1
TOP MARK
(SEE NOTE 6)
43
43
41
41
39
39
7
37
37
9
35
35
6.40 REF
2
44
R = 0.10
TYP
2
4
4
6
6
7
9
34
34
11
33
33
12
32
32
12
13
31
31
14
30
30
13
14
15
29
29
16
28
17
27
28
27
8.00 ± 0.10
11
0.20 ± 0.05
0.80 BSC
0.60 TYP
0.40 BSC
15
5.90 ±0.10
2.90 ±0.10
16
17
0.70 TYP
0.200 REF
0.75 ± 0.05
26
25 24 23 22 21 20 19
18
(UHG39) QFN 0410 REV B
3.20 REF
BOTTOM VIEW—EXPOSED PAD
18 19 20 21 22 23 24 25 26
0.00 – 0.05
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
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 0.20mm ON ANY SIDE
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
3597fa
22
LT3597
Revision History
REV
DATE
DESCRIPTION
A
7/11
Revised Maximum limit for LED1-3 Pin Leakage Current in the Electrical Characteristics section.
PAGE NUMBER
Made text edits in ‘LED Current Derating Using the CTRLM Pin’ and ‘Fault Flag’ sections in the Applications
Information section.
4
15, 17
3597fa
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.
23
LT3597
Typical Application
Triple Step-Down RGB Single Pixel LED Driver, 100mA Current
VIN
48V
10µF
VIN
270k
BOOST2
0.1µF 100µH
EN/UVLO
SW2
BOOST1
DA2
SW1
FB2
DA1
VOUT2
LED2
BOOST3
91k
VOUT1
0.1µF
PWM
2V/DIV
97k
G
9.1k
3.3µF
9.1k
VCC
5V
10µF
VOUT2
3.3µF
100µH
97k
R
10,000:1 Dimming at 100Hz
FB1
LT3597
0.1µF 100µH
VOUT1
LED1
BIAS
10µF
VOUT3
SW3
3.3µF
200ns/DIV
97k
3597 TA06b
DA3
100k
9.1k
FB3
FAULT
PWM1:3
CTRL1:3
SYNC
RT
33.2k
ILED
50mA/DIV
ISET1
VOUT3
LED3
VREF
ISET2
ISET3
GND
TSET
CTRLM
3597 TA06
20k
20k
10k
20k
82.5k
B
VREF
49.9k
100k
Related Parts
PART NUMBER DESCRIPTION
COMMENTS
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
LT3492
60V, 2.1MHz 3-Channel (ILED = 1A) Full Featured LED
Driver
VIN: 3V to 30V (40VMAX), VOUT(MAX) = 60V, True Color PWM Dimming = 3000:1,
ISD < 1µA, 4mm × 5mm QFN-28 Package
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
LT3590
48V, 850kHz 50mA Buck Mode LED Driver
VIN: 4.5V to 55V, True Color PWM Dimming = 200:1,
ISD < 15µA, 2mm × 2mm DFN-6 and SC70 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
LT3596
60V, 1MHz 3-Channel Full Featured LED Driver
VIN: 6V to 60V, VOUT(MAX) = 40V, True Color PWM Dimming = 10,000:1,
ISD ≤ 2µA, 5mm × 8mm QFN-52 Package
LT3598
44V, 1.5A, 2.5MHz Boost 6-Channel LED Driver
VIN: 3V to 30V (40VMAX), VOUT(MAX) = 44V, True Color PWM Dimming = 1000:1,
ISD < 1µA, 4mm × 4mm QFN-24 Package
LT3599
2A Boost Converter with Internal 4-String 150mA LED VIN: 3V to 30V, VOUT(MAX) = 44V, True Color PWM Dimming = 1000:1,
ISD < 1µA, 5mm × 5mm QFN-32 and TSSOP-28 Packages
Ballaster
LT3754
16-Channel x 50mA LED Driver with 60V Boost
Controller and PWM Dimming
VIN: 6V to 40V, VOUT(MAX) = 60V, True Color PWM Dimming = 3000:1,
ISD < 2µA, 5mm × 5mm QFN-52 Package
LT3760
8-Channel x 100mA LED Driver with 60V Boost
Controller and PWM Dimming
VIN: 6V to 40V, VOUT(MAX) = 60V, True Color PWM Dimming = 3000:1,
ISD < 2µA, TSSOP-28 Package
3597fa
24 Linear Technology Corporation
LT 0711 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 2011