Linear LT3592EMSE 500ma wide input voltage range step-down led driver with 10:1 dimming Datasheet

LT3592
500mA Wide Input Voltage
Range Step-Down LED Driver
with 10:1 Dimming
DESCRIPTION
FEATURES
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Wide Input Voltage Range
Operation from 3.6V to 36V
Resistor Adjustable 400kHz–2.2MHz Switching
Frequency
Shorted and Open LED Protected
Internal Switch Current Sense Resistor
External Resistor Programs LED Current, Pin
Selects 10:1 Ratio
50mA/500mA LED Current Settings
Catch Diode Current Sense to Prevent Runaway at
High VIN
Small Thermally Enhanced 10-Lead DFN
(2mm × 3mm) and MSOP-10 Packages
APPLICATIONS
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The LT®3592 is a ﬁxed frequency step-down DC/DC converter designed to operate as a constant-current source.
An external sense resistor monitors the output current
allowing accurate current regulation, ideal for driving
high current LEDs. The output current can be dimmed
by a factor of 10 using an external signal for nighttime
brake lights.
The high switching frequency offers several advantages by
permitting the use of a small inductor and small ceramic
capacitors. Small components combined with the LT3592’s
10-pin DFN leadless surface mount package save space and
cost versus alternative solutions. The constant switching
frequency combined with low-impedance ceramic capacitors result in low, predictable output ripple.
A wide input voltage range of 3.6V to 36V makes the
LT3592 useful in a variety of applications. Current mode
PWM architecture provides fast transient response and
cycle-by-cycle current limiting. Thermal shutdown provides
additional protection.
Automotive Signal Lighting
Industrial Lighting
Constant-Current, Constant Voltage Supplies
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
50/500mA Two Series Red LED Driver
Efﬁciency for 2 Red LEDs, L = 10μH, 900kHz
100
VIN
7V TO 32V
VIN
1μF
BOOST
95
0.1μF 10μH
LT3592
90
ON
BRAKE
DA
CAP
SHDN
BRIGHT
OUT
0.4Ω
GND
4.7μF
BRIGHT 500mA
85
80
75
70
65
51k
RT
140k
900kHz
+
200/20mV
–
EFFICIENCY (%)
SW
60
VFB
55
10k
50
3592 TA01a
4
8
16
12
20
INPUT VOLTAGE (V)
24
28
3592 TA01b
3592fc
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LT3592
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN, BRIGHT Voltages ................................ –0.3V to 36V
BOOST Voltage .........................................................60V
BOOST above SW pin ...............................................30V
CAP, OUT Voltages (OUT ≤ CAP) ...............................30V
VFB Voltage .................................................................4V
RT Voltage ...................................................................6V
SHDN Voltage ............................................................VIN
DA Pin Current (Average)..................... –1.2A (sourcing)
Operating Temperature Range (Notes 2, 3)
LT3592E ............................................. –40°C to 125°C
LT3592I .............................................. –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
PIN CONFIGURATION
TOP VIEW
RT
1
BRIGHT
2
TOP VIEW
10 VFB
RT
BRIGHT
SHDN
VIN
DA
9 OUT
11
SHDN
3
VIN
4
7 BOOST
DA
5
6 SW
8 CAP
DDB PACKAGE
10-LEAD (3mm s 2mm) PLASTIC DFN
θJA = 76°C/W, θJC = 13.5°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
1
2
3
4
5
11
10
9
8
7
6
VFB
OUT
CAP
BOOST
SW
MSE PACKAGE
10-LEAD PLASTIC MSOP
θJA = 38°C/W, θJC = 8°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3592EDDB#PBF
LT3592EDDB#TRPBF
LDCQ
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT3592IDDB#PBF
LT3592IDDB#TRPBF
LDCQ
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT3592EMSE#PBF
LT3592EMSE#TRPBF
LTDCR
10-Lead Plastic MSOP
–40°C to 125°C
LT3592IMSE#PBF
LT3592IMSE#TRPBF
LTDCR
10-Lead Plastic MSOP
–40°C to 125°C
LEAD BASED FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3592EDDB
LT3592EDDB#TR
LDCQ
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT3592IDDB
LT3592IDDB#TR
LDCQ
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT3592EMSE
LT3592EMSE#TR
LTDCR
10-Lead Plastic MSOP
–40°C to 125°C
LT3592IMSE
LT3592IMSE#TR
LTDCR
10-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.
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/
3592fc
2
LT3592
ELECTRICAL CHARACTERISTICS
The l denotes the speciﬁcations which apply over the full operating
temperature range, otherwise speciﬁcations are at TA = 25°C. VIN = 12V, VBOOST = 16V, VOUT = 4V unless otherwise noted. (Note 2)
PARAMETER
CONDITIONS
MIN
TYP
MAX
3.25
3.6
2
0.1
3
2
mA
μA
190
18
200
20
210
22
mV
mV
–0.8
–1
–1.2
A
450
1000
2.5
kHz
kHz
MHz
l
Minimum Input Voltage
Input Quiescent Current in Shutdown
Not Switching
VSHDN = 0.3V
CAP to OUT Voltage
0.4Ω CAP to OUT
BRIGHT = 1.4V
BRIGHT = 0.3V
l
l
DA Pin Current to Stop OSC
Switching Frequency
RT = 357k
RT = 140k
RT = 48.7k
350
800
1.9
400
900
2.2
Maximum Duty Cycle
RT = 140k
90
94
SHDN Input High Voltage
V
SHDN Input Low Voltage
0.3
1.4
l
0.85
V
V
BRIGHT Input Low Voltage
Switch Current Limit (Note 4)
V
%
2.3
BRIGHT Input High Voltage
UNITS
1.25
0.3
V
1.5
A
Switch VCESAT
ISW = 500mA
300
Boost Pin Current
ISW = 500mA
20
30
mA
1
10
μA
2.5
Switch Leakage Current
Minimum Boost Voltage (VBOOST – VIN)
VOUT = 4V
1.8
Boost Diode Forward Voltage
IDIO = 50mA
800
VFB Voltage
OUT = CAP = 4V, Bright = 12V
l
1.185
VFB Input Leakage Current
VFB = 1.21V
l
–250
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 LT3592E is guaranteed to meet performance speciﬁcations
from 0°C to 125°C junction temperature. Speciﬁcations over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LT3592I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The operating lifetime is derated at junction
temperatures greater than 125°C.
1.21
mV
V
mV
1.235
V
250
nA
Note 3: This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed the maximum operating junction temperature
when overtemperature protection is active. Continuous operation above
the speciﬁed maximum operating junction temperature may result in
device degradation or failure.
Note 4: Switch Current Measurements are performed when the outputs
are not switching. Slope compensation reduces current limit at higher duty
cycles.
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LT3592
TYPICAL PERFORMANCE CHARACTERISTICS
Efﬁciency (2 Red LEDS,
L = 10μH, 900kHz)
(TA = 25°C, unless otherwise noted)
Efﬁciency (1 Red LED,
L = 6.8μH, 900kHz)
Efﬁciency (2 Red LEDs,
L = 22μH, 400kHz)
100
100
100
95
95
95
90
90
BRIGHT (500mA)
EFFICIENCY (%)
EFFICIENCY (%)
80
75
70
65
60
75
70
65
60
55
50
50
45
45
40
40
8
16
12
20
INPUT VOLTAGE (V)
28
24
BRIGHT (500mA)
80
55
4
90
85
EFFICIENCY (%)
85
80
75
70
65
60
55
50
4
8
16
12
20
INPUT VOLTAGE (V)
28
24
3592 G01
95
11
11
90
10
10
OUTPUT VOLTAGE (V)
70
65
OUTPUT VOLTAGE (V)
12
EFFICIENCY (%)
12
75
9
8
7
6
5
7
6
5
4
4
3
3
50
2
16
12
20
INPUT VOLTAGE (V)
28
24
2
2
4
6
8
INPUT VOLTAGE (V)
3592 G04
450
10
400
9
350
8
7
6
100
3
50
0
16
3592 G07
10
12
375
200
4
14
6
8
INPUT VOLTAGE (V)
400
250
150
6
10
12
8
INPUT VOLTAGE (V)
4
Switch Voltage Drop at 500mA
vs Temperature
300
5
4
2
3592 G06
VIN – VSW (mV)
11
VIN – VSW (mV)
500
2
12
Switch Voltage Drop
vs Switch Current
12
2
10
3592 G05
Minimum VIN for 500mA Output
Current vs VOUT, L = 4.7μH,
f = 2.2MHz (LED Loads)
OUTPUT VOLTAGE (V)
8
55
8
28
24
9
60
4
16
12
20
INPUT VOLTAGE (V)
Minimum VIN for 500mA Output
Current vs VOUT, L = 6.8μH,
f = 900kHz (LED Loads)
100
80
8
3592 G03
Minimum VIN for 500mA Output
Current vs VOUT, L = 22μH,
f = 400kHz (LED Loads)
BRIGHT (500mA)
4
3592 G02
Efﬁciency (2 Red LEDs,
L = 4.7μH, 2.2MHz)
85
BRIGHT (500mA)
85
350
325
300
275
0
100 200 300 400 500 600 700 800
SWITCH CURRENT (mA)
3592 G08
250
–50
0
100
50
TEMPERATURE (°C)
150
3592 G09
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LT3592
TYPICAL PERFORMANCE CHARACTERISTICS
Undervoltage Lockout
vs Temperature
Switching Frequency
vs Temperature
1400
RT = 48.7k
2100
1900
1700
3.3
fSW (kHz)
UNDERVOLTAGE LOCKOUT (V)
Current Limit During Soft Start
2300
SWITCH CURRENT LIMIT (mA)
3.4
3.2
1500
1300
1100
RT = 140k
900
700
500
3.1
–50
0
50
100
TEMPERATURE (°C)
300
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
150
1000
800
600
400
0
0.5
3592 G11
SWITCH CURRENT LIMIT (A)
2000
1500
1000
500
1.50
1.3
1.45
1.2
1.40
1.1
1
0.9
0.8
0.7
0.6
0
600 800 1000 1200 1400 1600 1800 2000 2200
SHDN VOLTAGE (mV)
0.5
2
2.5
1.35
TYPICAL
1.30
1.25
1.20
1.15
1.10
1.05
0
20
40
60
DUTY CYCLE (%)
80
100
1.00
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
3592 G14
3592 G13
3592 G15
Operating Waveforms,
Discontinuous Mode
Operating Waveforms
500ns/DIV
1.5
VSHDN (V)
Switch Current Limit
1.4
SWITCH CURRENT LIMIT (A)
RT = 48.7k
1
3592 G12
Switch Current Limit
Frequency Foldback
2500
1200
200
RT = 357k
3592 G10
FREQUENCY (kHz)
(TA = 25°C, unless otherwise noted)
3592 G16
VSW
5V/DIV
VSW
5V/DIV
VCAP
10mV/DIV
AC-COUPLED
VCAP
10mV/DIV
AC-COUPLED
IL
500mA/DIV
IL
500mA/DIV
500ns/DIV
3592 G17
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LT3592
TYPICAL PERFORMANCE CHARACTERISTICS
VBRIGHT vs VOUT
(TA = 25°C, unless otherwise noted)
VDIM vs VOUT
210
25
24
23
VBRIGHT (mV)
VCAP – VOUT (mV)
VCAP – VOUT (mV)
205
200
195
22
21
VDIM (mV)
20
19
18
17
16
190
0
2
4
6
8
15
12
10
VOUT (V)
0
2
4
6
VOUT (V)
8
3592 G18
Boost Diode Voltage vs Current
Switching Frequency vs RT
3000
VBSTDIO
0.9
2500
FREQUENCY (kHz)
DIODE FORWARD VOLTAGE (V)
12
3592 G19
1.0
0.8
0.7
0.6
0.5
0.4
10
2000
1500
1000
500
0
50
100
150
DIODE CURRENT (mA)
200
3592 G20
0
30 60 90 120 150 180 210 240 270 300 330 360
RT (kΩ)
3592 G21
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LT3592
PIN FUNCTIONS
RT (Pin 1): Programs the frequency of the internal oscillator.
Connect a resistor from RT to ground. Refer to Table 1 or
the Typical Performance Characteristics for resistor values
that result in desired oscillator frequencies.
BRIGHT (Pin 2): Used to program a 10:1 dimming ratio
for the LED current. Drive this pin above 1.4V to command
maximum intensity or below 0.3V to command minimum
intensity. This pin can be PWMed at 150Hz for brightness
control between the 1x and 10x current levels.
SHDN (Pin 3): Used to shutdown the switching regulator
and the internal bias circuits. This pin can be PWMed at
150Hz for brightness control.
VIN (Pin 4): Supplies current to the LT3592’s internal circuitry and to the internal power switches. Must be locally
bypassed. For automotive applications, a pi network with a
cap from VIN to GND, a series inductor connected between
VIN and the power source, and another cap from the far
end of the inductor to GND is recommended.
DA (Pin 5): Allows the external catch diode current to be
sensed to prevent current runaway, such as when VIN is
high and the duty cycle is very low. Connect this pin to
the anode of the external catch Schottky diode.
SW (Pin 6): The SW pin is the output of the internal power
switch. Connect this pin to the inductor and the cathode
of the switching diode.
BOOST (Pin 7): Provides a drive voltage, higher than the
input voltage to the internal bipolar NPN power switch.
BOOST will normally be tied to the SW pin through a 0.1μF
capacitor. An internal Schottky is provided for the boost
function and an external diode is not needed. An external
Schottky diode should be connected between BOOST and
CAP for single LED applications or whenever a higher
BOOST voltage is desired.
CAP (Pin 8): Output of the step-down converter and also
an input to the LED current sense ampliﬁer. Connect the
ﬁlter capacitor, inductor, and the top of the external LED
current sense resistor to this pin.
OUT (Pin 9): Drives the LED or LEDs and is the other
input to the LED current sense ampliﬁer. Connect this pin
to the anode of the top LED in the string, the bottom of
the external LED current sense resistor, and the top of the
VFB resistor divider.
VFB (Pin 10): The feedback node for the output voltage
control loop. Tie this node to a resistor divider between OUT
and GND to set the maximum output voltage of the stepdown converter according to the following formula:
VOUT = 1.21•
R1+ R2
R2
where R1 connects between OUT and VFB and R2 connects
between VFB and GND.
Exposed Pad (Pin 11): Ground. The underside exposed
pad metal of the package provides both electrical contact
to ground and good thermal contact to the printed circuit
board. The device must be soldered to the circuit board
for proper operation.
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LT3592
BLOCK DIAGRAM
L3
L2
BATT
C2C
C2B
C2A
4
BRAKE
VIN
BRIGHT
2
RSENSE
9
LED1
R1
R2
10R
–
BOOST
gm =
10
LED2
OUT
+
VFB
–
CAP
8
+
R
6
R
1.21V
–
–
+
VC
7
C3
R
Q
Q1
S
SW
L1
6
D1
GND
DA
–
REG/UVLO
R3
C1
+
3
SHDN
VIN
C4
5
OSC
1
RT
11
GND
RT
3592 BD
3592fc
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LT3592
OPERATION
The LT3592 is a constant frequency, current mode stepdown LED driver. An internal oscillator that is programmed
by a resistor from the RT pin to ground enables an RS
ﬂip-ﬂop, turning on the internal 1.25A power switch Q1.
An ampliﬁer and comparator monitor the current ﬂowing
between the VIN and SW pins, turning the switch off when
this current reaches a level determined by the voltage at
VC. An error ampliﬁer that servos the VC node has two
inputs, one from a voltage measurement and one from a
current measurement.
error ampliﬁer output means less output current. Current
limit is provided by an active clamp on the VC node, and
this node is also clamped to the SHDN pin. Soft-start is
implemented by ramping the SHDN pin using an external
resistor and capacitor.
An instrumentation ampliﬁer measures the drop across
an external current sense resistor between the CAP and
OUT pins and applies a gain of 60 (BRIGHT low for dim
mode) or 6 (BRIGHT high for bright mode) to this signal
and presents it to one negative error amp input. The output
of a external resistor divider between OUT and ground is
tied to the VFB pin and presented to a second negative error
amp input. Whichever input is higher in voltage will end up
controlling the loop, so a circuit in which current control
is desired (as for driving a LED) will be set up such that
the output of the instrumentation amp will be higher than
the VFB pin at the current level that is desired. The voltage
feedback loop will act to limit the output voltage and prevent
circuit damage if an LED should go open circuit.
The switch driver operates from the input of the BOOST
pin. An external capacitor and internal diode are used to
generate a voltage at the BOOST pin that is higher than the
input supply, which allows the driver to fully saturate the
internal bipolar NPN power switch for efﬁcient operation.
An external diode can be used to make the BOOST drive
more effective at low output voltage.
The positive input to the error amp is a 1.21V reference,
so the voltage loop forces the VFB pin to 1.21V and the
current loop forces the voltage difference between CAP
and OUT to be 200mV for BRIGHT mode and 20mV for
DIM mode. A rise in the output of the error ampliﬁer
results in a increase in output current, and a fall in the
An internal regulator provides power to the control
circuitry and also includes an undervoltage lockout to
prevent switching when VIN is less than 3.25V. If SHDN
is low, the output is disconnected and the input current
is less than 2μA.
The oscillator reduces the LT3592’s operating frequency
when the voltage at the OUT pin is low. This frequency
foldback helps to control the output current during startup
and overload.
The anode of the catch diode for the step-down circuit is
connected to the DA pin to provide a direct sense of the
current in this device. If this diode’s current goes above a
level set by an internal catch diode current limit circuit, the
oscillator frequency is slowed down. This prevents current
runaway due to minimum on time limitations at high VIN
voltages. This function can easily be disabled by tying the
DA pin and the catch diode anode to ground.
3592fc
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LT3592
APPLICATIONS INFORMATION
Oscillator
The BRIGHT mode current is given by:
The frequency of operation is programmed by an external
resistor from RT to ground. Table 1 shows RT values for
commonly used oscillator frequencies, and refer to the Typical Performance Characteristics curve for other values.
Table 1. RT Values for Selector Oscillator Frequencies
fOSC
RT
400kHz
357k
900kHz
140k
2.2MHz
48.7k
FB Resistor Network
The output voltage limit is programmed with a resistor
divider between the output and the VFB pin. This is the
voltage that the output will be clamped to in case the LED
goes open circuit. Choose the resistors according to
IBRIGHT = 200mV/RSENSE
The DIM mode current is 10% of the BRIGHT mode value.
The maximum allowed DC value of the BRIGHT mode current is 500mA. When the recommended component values
are used in a 900kHz 2 LED application, the transient from
switching between BRIGHT and DIM currents will be less
than 50μs in duration.
The sense resistor used should exhibit a low TC to keep
the LED current from drifting as the operating temperature
changes.
The BRIGHT pin can tolerate voltages as high as 36V and
can be safely tied to VIN even in high voltage applications,
but it also has a low threshold voltage (~0.7V) that allows
it to interface to logic level control signals.
Input Voltage Range
R1 = R2([VOUT/1.21V] – 1)
Be sure to choose VOUT such that it does not interfere with
the operation of the current control loop; it should be set
at least 10% above the maximum expected LED voltage
for the selected BRIGHT output current. R2 should be 20k
or less to avoid bias current errors. An optional phaselead capacitor of 22pF between VOUT and VFB reduces
light-load ripple.
Output Current Selection
The output current levels are programmed by the value of
the external current sense resistor between CAP and OUT.
The maximum allowed input voltage for the LT3592 is
36V. The minimum input voltage is determined by either
the LT3592’s minimum operating voltage of 3.6V or by
its maximum duty cycle. The duty cycle is the fraction of
time that the internal switch is on and is determined by
the input and output voltages:
DC =
VOUT + VD
VIN – VSW + VD
where VD is the forward voltage drop of the catch diode
(~0.4V) and VSW is the voltage drop of the internal switch
Table 2. Inductor Vendor Information
SUPPLIER
PHONE
FAX
WEBSITE
Panasonic
(800) 344-2112
Vishay
(402) 563-6866
(402) 563-6296
www.vishay.com/resistors
Coilcraft
(847) 639-6400
(847) 639-1469
www.coilcraft.com
CoEv Magnetics
(800) 227-7040
(650) 361-2508
www.circuitprotection.com/magnetics.asp
Murata
(814) 237-1431
(800) 831-9172
(814) 238-0490
www.murata.com
Sumida
USA: (847) 956-0666
USA: (847) 956-0702
www.sumida.com
Japan: 81(3) 3607-5111 Japan: 81(3) 3607-5144
TDK
(847) 803-6100
(847) 803-6296
www.component.tdk.com
TOKO
(847) 297-0070
(847) 699-7864
www.tokoam.com
www.panasonic.com/industrial/components/components.html
3592fc
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LT3592
APPLICATIONS INFORMATION
(~0.4V at maximum load). This leads to a minimum input
voltage of:
VIN(MIN) =
VOUT + VD
– VD + VSW
DCMAX
Minimum On Time
with DCMAX = 0.90.
The maximum input voltage is determined by the absolute
maximum ratings of the VIN and BOOST pins. The continuous mode operation, the maximum input voltage is
determined by the minimum duty cycle, which is dependent
upon the oscillator frequency:
DCMIN = fOSC • 70nsec
VIN(MAX) =
VOUT + VD
– VD + VSW
DCMIN
Note that this is a restriction on the operating input voltage
for continuous mode operation. The circuit will tolerate
transient inputs up to the absolute maximum of the VIN
and BOOST pins. The input voltage should be limited to
VOUT
50mV/DIV
IL
500mA/DIV
VSW
20V/DIV
1μs/DIV
the VIN absolute maximum range (36V) during overload
conditions (short circuit or startup).
3592 F01
Figure 1.
The LT3592 will still regulate the output properly at input
voltages that exceed VIN(MAX) (up to 36V); however, the
output voltage ripple increases as the input voltage is
increased.
Figure 1 illustrates switching waveforms in a 2.2MHz single
red LED application near VIN(MAX) = 24V.
As the input voltage is increased, the part is required to
switch for shorter periods of time. Delays associated with
turning off the power switch dictate the minimum on time
of the part. The minimum on time for the LT3592 is ~70ns.
Figure 2 illustrates the switching waveforms when the
input voltage is increased to VIN = 26V.
Now the required on time has decreased below the minimum on time of 70ns. Instead of the switch pulse width
becoming narrower to accommodate the lower duty
cycle requirement, the switch pulse width remains ﬁxed
at 70ns. In Figure 2, the inductor current ramps up to a
value exceeding the load current and the output ripple
increases to about 70mV. The part then remains off until
the output voltage dips below the programmed value
before it switches again.
Provided that the load can tolerate the increases output
voltage ripple and the the components have been properly
selected, operation about VIN(MAX) is safe and will not damage the part. Figure 3 illustrates the switching waveforms
when the input voltage is increased to 36V.
VOUT
50mV/DIV
VOUT
50mV/DIV
IL
500mA/DIV
IL
500mA/DIV
VSW
20V/DIV
VSW
20V/DIV
1μs/DIV
Figure 2.
3592 F02
1μs/DIV
3592 F03
Figure 3.
3592fc
11
LT3592
APPLICATIONS INFORMATION
As the input voltage increases, the inductor current ramps
up more quickly, the number of skipped pulses increases,
and the output voltage ripple increases. For operation
above VIN(MAX), the only component requirement is that
they be adequately rated for operation at the intended
voltage levels.
The LT3592 is robust enough to survive prolonged operation under these conditions as long as the peak inductor
current does not exceed 1.2A. Inductor saturation due to
high current may further limit performance in this operating regime.
Inductor Selection and Maximum Output Current
A good ﬁrst choice for the inductor value is:
L = 1.2A •
( VOUT + 0.2V + VD )
ƒ
where VD is the forward voltage drop of the catch diode
(~0.4V), f is the switching frequency in MHz and L is in μH.
With this value, there will be no subharmonic oscillation for
applications with 50% or greater duty cycle. For low duty
cycle applications in which VIN is more than three times
VOUT, a good guide for the minimum inductor value is
( V V 0.2V ) ( VOUT + 0.2V + VD ) L = 1.7 • IN OUT
•
ƒ
VIN VSW + VD where VSW is the switch voltage drop (about 0.3V at
500mA). The inductor’s RMS current rating must be greater
than your maximum load current and its saturation current
should be about 30% higher. For robust operation in fault
conditions, the saturation current should be above 1.5A. To
keep efﬁciency high, the series resistance (DCR) should be
less than 0.1Ω. Table 2 lists several inductor vendors.
Of course, such a simple design guide will not always result in the optimum inductor for your application. A larger
value provides a higher maximum load current and reduces
output voltage ripple at the expense of a slower transient
response. If your load is lower than 500mA, then you can
decrease the value of the inductor and operate with higher
ripple current. This allows you to use a physically smaller
inductor, or one with a lower DCR resulting in higher efﬁciency. There are several graphs in the Typical Performance
Characteristics section of this data sheet that show the
maximum load current as a function of input voltage and
inductor value for several popular output voltages. Low
inductance may result in discontinuous mode operation,
which is acceptable, but further reduces maximum load
current. For details of the maximum output current and
discontinuous mode operation, see Linear Technology
Application Note 44.
Catch Diode
Depending on load current, a 500mA to 1A Schottky diode is recommended for the catch diode, D1. The diode
must have a reverse voltage rating equal to or greater
than the maximum input voltage. The ON Semiconductor
MBRA140T3 and Central Semiconductor CMMSH1-40 are
good choices, as they are rated for 1A continuous forward
current and a maximum reverse voltage of 40V.
Input Filter Network
For applications that only require a capacitor, bypass VIN
with a 1μF or higher ceramic capacitor of X7R or X5R
type. Y5V types have poor performance over temperature and applied voltage and should not be used. A 1μF
ceramic capacitor is adequate to bypass the LT3592 and
will easily handle the ripple current. However, if the input
power source has high impedance, or there is signiﬁcant
inductance due to long wires or cables, additional bulk
capacitance might be necessary. The can be provided
with a low performance (high ESR) electrolytic capacitor
in parallel with the ceramic device.
Some applications, such as those in automobiles, may
require extra ﬁltering due to EMI/EMC requirements. In
these applications, very effective EMI ﬁltering can be provided by a capacitor to ground right at the source voltage,
a series ferrite bead, and a pi ﬁlter composed of a capacitor
to ground, a series inductor, and another capacitor directly
from the device pin to ground (see the Block Diagram for
an example). Typical values for the ﬁlter components are
10nF for C2C, a ferrite bead that is ~220Ω at 100MHz for
L2, 3.3μF for C2B, 10μH for L3, and 1μF for C2A.
Step-down regulators draw current from the input supply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage ripple
3592fc
12
LT3592
APPLICATIONS INFORMATION
at the LT3592 and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 1μF
capacitor is capable of this task, but only if it is placed
close to the LT3592 and catch diode (see the PCB layout
section). A second precaution regarding the ceramic input
capacitor concerns the maximum input voltage rating of
the LT3592. A ceramic input capacitor combined with trace
or cable inductance forms a high quality (underdamped)
tank circuit. If the LT3592 circuit is plugged into a live
supply, the input voltage can ring to twice its nominal
value, possibly exceeding the LT3592’s voltage rating.
This situation can easily be avoided, as discussed in the
Hot Plugging Safety section. For more details, see Linear
Technology Application Note 88.
Output Capacitor
For most 2.2MHz LED applications, a 3.3μF or higher
output capacitor is sufﬁcient for stable operation. A
900kHz application should use a 4.7μF or higher output
capacitor. 400kHz applications require a 22μF or higher
output capacitor. The minimum recommended values
should provide an acceptable (if somewhat underdamped)
transient response, but larger values can always be used
when extra damping is required or desired.
The output capacitor ﬁlters the inductor current to generate
an output with low voltage ripple. It also stores energy in
order to satisfy transient loads and stabilizes the LT3592’s
control loop. Because the LT3592 operates at a high frequency, minimal output capacitance is necessary. In addition,
the control loop operates well with or without the presence
of signiﬁcant output capacitor equivalent series resistance
(ESR). Ceramic capacitors, which achieve very low output
ripple and small circuit size, are therefore an option.
You can estimate output ripple with the following
equation:
VRIPPLE =
ΔILP−P
8 • ƒ • COUT
where ΔILP-P is the peak-to-peak ripple current in the inductor. The RMS content of this ripple is very low, so the
RMS current rating of the output capacitor is usually not
a concern. It can be estimated with the formula:
IC(RMS) =
ΔIL
12
The low ESR and small size of ceramic capacitors make
them the preferred type for LT3592 applications. Not all
ceramic capacitors are the same, though. Many of the
higher value ceramic capacitors use poor dielectrics with
high temperature and voltage coefﬁcients. In particular,
Y5V and Z5U types lose a large fraction of their capacitance
with applied voltage and at temperature extremes.
Because loop stability and transient response depend on
the value of COUT, this loss may be unacceptable. Use X7R
and X5R types. Table 3 lists several capacitor vendors.
Figure 4 shows the transient response of the LT3592 when
switching between DIM and BRIGHT current levels with
two output capacitor choices. The output load is two series
Luxeon K2 Red LEDs, the DIM current is 50mA and the
BRIGHT current is 500mA, and the circuit is running at
900kHz. The upper photo shows the recommended 4.7μF
value. The second photo shows the improved response
resulting from a larger output capacitor.
Table 3. Capacitor Vendor Information
SUPPLIER
PHONE
FAX
AVX
(803) 448-9411
(803) 448-1943
www.avxcorp.com
WEBSITE
Sanyo
(619) 661-6322
(619) 661-1055
www.sanyovideo.com
Taiyo Yuden
(408) 573-4150
(408) 573-4159
www.t-yuden.com
TDK
(847) 803-6100
(847) 803-6296
www.component.tdk.com
3592fc
13
LT3592
APPLICATIONS INFORMATION
VOUT
ILED
VSW
C = 4.7μF
100μs/DIV
VOUT
ILED
VSW
C = 10μF
100μs/DIV
3592 F04
Figure 4. Transient Load Response of the LT3592 with Different Output Capacitors
OPTIONAL
BOOST
D2
D2
BOOST
C3
CAP
LT3592 SW
BATT
C3
CAP
LT3592 SW
VIN
BATT
GND
DA
VIN
GND
DA
3592 F05a
3592 F05b
(5a)
(5b)
Figure 5. Two Circuits for Generating the Boost Voltage
BOOST Pin Considerations
The capacitor C3 and an internal Schottky diode from
the CAP to the BOOST pin are used to generate a boost
voltage that is higher than the input voltage. An external
fast switching Schottky diode (such as the BAS40) can
be used in parallel with the internal diode to make this
boost circuit even more effective. In most cases, a 0.1μF
capacitor works well for the boost circuit. The BOOST pin
must be at least 2.5V above the SW pin for best efﬁciency.
For output voltages above 12V, use a 0.1μF cap and an
external boost diode (such as a BAS40) connected in
parallel with the internal Schottky diode, anode to CAP
and cathode to BOOST. For outputs between 3.3V and
12V, the 0.1μF cap and the internal boost diode will be
effective. For 3V to 3.3V outputs, use a 0.22μF capacitor.
For output between 2.5V and 3V, use a 0.47μF capacitor
and an external Schottky diode connected as shown in
Figure 5a. For lower output voltages, the external boost
diode’s anode can be tied to the input voltage. This connection is not as efﬁcient as the others because the BOOST
pin current comes from a higher voltage. The user must
also be sure that the maximum voltage rating of the BOOST
pin is not exceeded.
3592fc
14
LT3592
APPLICATIONS INFORMATION
this restricts the input range to one-half of the absolute
maximum rating of the BOOST pin.
At light loads, the inductor current becomes discontinuous
and the effective duty cycle can be very high. This reduces
the minimum input voltage to about 400mV above VCAP.
At higher load currents, the inductor current is continuous and the duty cycle is limited by the maximum duty
cycle of the LT3592, requiring a higher input voltage to
maintain regulation.
Soft-Start
The SHDN pin can be used to soft-start the LT3592, reducing
the maximum input current during startup. The SHDN pin
is driven through an external RC ﬁlter to create a voltage
ramp at this pin. Figure 7 shows the startup waveforms
with and without the soft-start circuit. By choosing a large
RC time constant, the peak startup current can be reduced
to programmed LED current, with no overshoot. Choose
the value of the resistor so that it can supply 20μA when
the SHDN pin reaches 2.3V.
12
12
11
11
11
10
10
10
9
9
9
8
7
6
5
LED VOLTAGE (V)
12
LED VOLTAGE (V)
LED VOLTAGE (V)
The minimum operating voltage of an LT3592 application
is limited by the undervoltage lockout (UVLO, ~3.25V) and
by the maximum duty cycle as outlined above. For proper
startup, the minimum input voltage is also limited by the
boost circuit. If the input voltage is ramped slowly, or the
LT3592 is turned on with its SHDN pin when the output is
already in regulation, then the boost capacitor might not
be fully charged. Because the boost capacitor is charged
with the energy stored in the inductor, the circuit will rely
on some minimum load current to get the boost circuit
running properly. This minimum load generally goes to
zero once the circuit has started. Figure 6 shows a plot
of minimum input voltage needed to start with a 500mA
output current versus output voltage with LED loads. For
LED applications, the output voltage will typically drop
rapidly after start due to diode heating, but this is not
a concern because the voltage to run is lower than the
voltage to start. The plots show the worst case situation
when VIN is ramping very slowly. For a lower startup
voltage, the boost diode’s anode can be tied to VIN, but
8
7
6
5
8
7
6
5
4
4
4
3
3
3
2
2
4
6
8
INPUT VOLTAGE (V)
400kHz, L = 22μH
10
12
3592 F06a
2
2
4
6
8
INPUT VOLTAGE (V)
900kHz, L = 6.8μH
10
12
3592 F06b
2
2
4
6
10
12
8
INPUT VOLTAGE (V)
2.2MHz, L = 4.7μH
14
16
3592 F06c
Figure 6. Input Voltage Needed to Start at 500mA Output Current vs LED Voltage
3592fc
15
LT3592
APPLICATIONS INFORMATION
LT3592
RUN
IL
500mA/DIV
SHDN
GND
3592 F07a
VSW
10V/DIV
VOUT
5V/DIV
50μs/DIV
RUN
15k
LT3592
IL
500mA/DIV
SHDN
0.1μF
GND
VSW
10V/DIV
3592 F07b
VOUT
5V/DIV
50μs/DIV
Figure 7. To Soft-Start the LT3592, Add a Resistor and Capacitor to the SHDN Pin
Shorted and Open LED Protection
In case of a shorted LED string or the OUT pin being
shorted to ground by any means, the current loop will
help to limit the output current for many conditions, but
the switch current may still reach the switch current limit
on some cycles despite the actions of the current loop.
For some conditions (especially cold), the output current
for shorted OUT will only be limited by the switch current
limit (which can be as high as 1.5A) and the switching
frequency foldback that occurs when OUT is close to
ground, and the current control loop will have little to
no effect. The total power dissipation will be quite low
in either case due to the frequency foldback and the fact
that the small current sense resistor will effectively be the
output load for shorted OUT. Peak switch and inductor
currents will be high, but the peaks will be brief and well
separated due to the lowered operating frequency. The
main concern in this condition is that the output inductor
not saturate and force the switch into an unsafe operating
condition of simultaneous high current and high voltage
drop. If the current sense resistor between CAP and OUT
becomes shorted or the CAP pin is shorted to ground, the
peak output current will be limited by the internal switch
current limit, which could be as high as 1.5A.
If an LED goes open circuit, the voltage control loop
through the R1-R2 resistor divider to FB will take control
and prevent the output voltages from ﬂying up close to
VIN. Program the desired open circuit voltage to a value
below the absolute maximum for the CAP and OUT pins
but well above the maximum possible forward drop of the
LED at the programmed BRIGHT current.
Reversed Input Protection
In some systems, the output will be held high when the
input to the LT3592 is absent. This may occur in battery
charging applications or in battery backup systems where
a battery or some other supply is diode ORed with the
LT3592’s output. If the VIN pin is allowed to ﬂoat and the
SHDN pin is held high (either by a logic signal or because
it is tied to VIN), then the LT3592’s internal circuitry will
draw its quiescent current through its SW pin. This is ﬁne
if the system can tolerate a few mA in this state. If you
3592fc
16
LT3592
APPLICATIONS INFORMATION
D4
VIN
VIN
VOUT
SW
LT3592
SHDN
GND
FB
+
BACKUP
3592 F08
D4: MBR0540
Figure 8. Circuit to Address Reversed Input and Backpowering Issues
CLOSING SWITCH
SIMULATES HOT PLUG
IIN
VIN
LT3592
VIN
+
+
GND
IIN
10A/DIV
1μF
VIN
20V/DIV
LOW
IMPEDANCE
ENERGIZED
32V SUPPLY
STRAY
INDUCTANCE
DUE TO 6 FEET
(2 METERS) OF
TWISTED PAIR
5μs/DIV
(9a)
VIN LT3592
+
+
+
10μF
50V
GND
IIN
10A/DIV
2.2μF
VIN
20V/DIV
5μs/DIV
(9b)
1Ω
LT3592
VIN
+
+
GND
IIN
10A/DIV
0.1μF
2.2μF
VIN
20V/DIV
5μs/DIV
(9c)
3493 F09
Figure 9. A Well Chosen Input Network Prevents Input Voltage Overshoot and
Ensures Reliable Operation When the LT3592 is Connected to a Live Supply
3592fc
17
LT3592
APPLICATIONS INFORMATION
The small size, robustness, and low impedance of ceramic
capacitors make them an attractive option for the input
bypass capacitor of LT3592 circuits. However, these capacitors can cause problems if the LT3592 is plugged into a
live supply (see Linear Technology Application Note 88 for
a complete discussion). The low loss ceramic capacitor
combined with stray inductance in series with the power
source forms an underdamped tank circuit, and the voltage at the VIN pin of the LT35392 can ring to twice the
nominal input voltage, possibly exceeding the LT3592’s
rating and damaging the part. If the input supply is poorly
controlled or the user will be plugging the LT3592 into an
energized supply, the input network should be designed
to prevent this overshoot.
Figure 9 shows the waveforms that result when an LT3592
circuit is connected to a 32V supply through six feet of 24
gauge twisted pair. The ﬁrst plot is the response with a 1μF
ceramic capacitor at the input. The input voltage rings as
high as 56V and the input current peaks at 16A.
One method of damping the tank circuit is to add another
capacitor with a series resistor to the circuit. In Figure 9b,
a tantalum chip capacitor has been added. This capacitor’s
high equivalent series resistance (ESR) damps the circuit
and eliminates the voltage overshoot. The extra capacitor
improves low frequency ripple ﬁltering and can slightly
improve the efﬁciency of the circuit, thought it is likely
to be the largest component in the circuit. An alternate
solution is shown in Figure 9c. A 1Ω resistor is added in
series with the input to eliminate the voltage overshoot
(it also reduces the peak input current). A 0.1μF capacitor
improves high frequency ﬁltering. This solution is smaller
and less expensive than the tantalum capacitor. For high
input voltages, the impact of the 1Ω resistor on efﬁciency
Frequency Compensation
The LT3592 uses current mode control to regulate the
loop, whether the current control or voltage control loop
is active. This simpliﬁes loop compensation. In particular,
the LT3592 does not require the ESR of the output capacitor for stability, allowing the use of ceramic capacitors
to achieve low output ripple and small circuit size. A low
ESR output capacitor will typically provide for a greater
margin of circuit stability than an otherwise equivalent
capacitor with higher ESR, although the higher ESR will
tend to provide a faster loop response. Figure 10 shows
an equivalent circuit for the LT3592 control loops, both for
current and voltage mode. Both use the same error ampliﬁer
and power section, but an additional voltage gain amp is
used in conjuction with the external current sense resistor
to implement output current control. The error ampliﬁer is
a transconductance type with ﬁnite output impedance. The
power section, consisting of the modulator, power switch,
and inductor, is modeled as a transconductance ampliﬁer
generating an output current proportional to the voltage
at the VC node. Note that the output capacitor integrates
this current, and that the capacitor on the VC node (CC)
integrates the error ampliﬁer output current, resulting in
gm = 0.7A/V
SW
0.7V
+
Hot Plugging Safely
is minor, reducing it by less than one half percent for a two
red series LED load in BRIGHT mode operating from 32V.
–
ground the SHDN pin, the SW pin current will drop to essentially zero. However, if the VIN pin is grounded while
the output is held high, then parasitic diodes inside the
LT3592 can pull large currents from the output through
the SW pin and the VIN pin. Figure 8 shows a circuit that
will run only when the input voltage is present and that
protects against a shorted or reversed input.
+
C1
BRIGHT
C1
30k
ESR
CAP
–
OUT
+
300k
RSENSE
RL
R1
gm = 1/5k
VFB
R2
1.2V
–
–
+
gm = 300μA/V
VC
RC
CC
GND
3592 F10
Figure 10. Model for Loop Response
3592fc
18
LT3592
APPLICATIONS INFORMATION
two poles in the loop. Rc provides a zero. With the recommended output capacitor, the loop crossover occurs above
the RCCC zero. This simple model works well as long as the
value of the inductor is not too high and the loop crossover
frequency is much lower than the switching frequency.
With a larger ceramic capacitor that will have lower ESR,
crossover may be lower and a phase lead capacitor (CPL)
across the feedback divider may improve the transient
response. Large electrolytic capacitors may have an ESR
large enough to create an additional zero, and the phase
lead might not be necessary. If the output capacitor is
different than the recommended capacitor, stability should
be checked across all operating conditions, including DIM
and BRIGHT current modes, voltage control via FB, input
voltage, and temperature.
PCB Layout
For proper operation and minimum EMI, care must be taken
during printed circuit board layout. Figure 11 shows the
recommended component placement with trace, ground
plane, and via locations. Note that large, switched currents
ﬂow in the LT3592’s VIN and SW pins, the catch diode (D1),
and the input capacitor (C2). The loop formed by these
components should be as small as possible and tied to
system ground in only one place. These components, along
with the inductor and output capacitor, should be placed on
the same side of the circuit board, and their connections
should be made on that layer. Place a local, unbroken ground
plane below these components, and tie this ground plane
to system ground at one location (ideally at the ground
terminal of the output capacitor C1). The SW and BOOST
nodes should be as small as possible. Finally, keep the
FB node small so that the ground pin and ground traces
will shield it from the SW and BOOST nodes. Include vias
near the exposed GND pad of the LT3592 to help remove
heat from the LT3592 to the ground plane.
High Temperature Considerations
The die temperature of the LT3592 must be lower than the
maximum rating of 125°C. This is generally not a concern
unless the ambient temperature is above 85°C. For higher
temperatures, extra care should be taken in the layout of
the circuit to ensure good heat sinking at the LT3592. The
maximum load current should be derated as the ambient
temperature approaches 125°C. The die temperature is
calculated by multiplying the LT3592 power dissipation
by the thermal resistance from junction to ambient.
Power dissipation within the LT3592 can be estimated
by calculating the total power loss from an efﬁciency
measurement and subtracting the catch diode loss. The
resulting temperature rise at full load is nearly independent
of input voltage. Thermal resistance depends upon the
layout of the circuit board, but 76°C/W is typical for the
3mm × 2mm DFN (DDB10) package, and 38°C/W is typical
for the MS10E package.
Higher Output Voltages
At higher output voltages, the choice of output capacitor
becomes especially critical. Many small case size ceramic
capacitors lose much of their rated capacitance well below
BRIGHT
SHDN
VIN
SYS GND
3592 F11
Figure 11. A Good PCB Layout Ensures Proper, Low EMI Operation
3592fc
19
LT3592
APPLICATIONS INFORMATION
their maximum voltage capability. If a capacitor with a
lower voltage rating is found to not be stable in a design,
it will often result in a smaller solution to choose a larger
capacitor value of the same voltage rating than to choose
one of the same capacitance and higher voltage rating. For
example, a 10μF, 10V ceramic capacitor might be smaller
than a 4.7μF, 16V part, if a 4.7μF, 10V capacitor is found
to not be adequate in a given application. The LT3592HV
can tolerate sustained output voltages of up to 25V. For
output voltages above 12V, use an external Schottky diode
for the boost circuit with the anode tied to CAP and the
cathode tied to BOOST (as shown in Figure 13).
Transient Performance with Voltage Control Loop
The voltage control loop transient characteristics are similar
to, but not identical to the current control loop. Figure 12
shows the transient for a 12V input application running at
900kHz with a 6.8μH inductor and a 4.7μF ceramic output
capacitor. The LT3592 is in BRIGHT (500mA) mode but
the current load is switched from 50mA to 450mA and
back, so the current control loop is not active for either
current level and the output voltage is regulated through
the resistive voltage divider to the FB pin.
Other Linear Technology Publications
Application Notes AN19, AN35, and AN44 contain more
detailed descriptions and design information for Step-down
regulators and other switching regulators. The LT1376 data
sheet has an extensive discussion of output ripple, loop
compensation, and stability testing. Design Note DN100
shows how to generate a bipolar output supply using a
Step-down regulator.
ILED
200mA/DIV
VOUT
1V/DIV
VSW
10V/DIV
3592 F12
10μs/DIV
Figure 12. Switching Transient When Going from 50mA to 500mA Current and Back in Voltage Mode
D2
BOOST
C3
CAP
LT3592 SW
BATT
VIN
GND
DA
3592 F13
Figure 13. Boost Circuit with External Schottky Diode for Output Voltages Above 12V
3592fc
20
LT3592
TYPICAL APPLICATIONS
Single Red LED Driver with Boost Diode to VIN Due to Low VOUT
1N4148
VIN
5V TO 16V
VIN
1μF
BOOST
0.1μF 15μH
LT3592
SW
MBRA120
DA
CAP
SHDN
OFF ON
0.4Ω
BRIGHT
FAULT
22μF
OUT
30k
RT
GND
357k
400kHz
LUXEON
LXK2-PD12-S00
VFB
10k
3592 TA02
50mA/500mA Two Series Red LED Driver
VIN
8V TO 32V
BEAD
10μH
VIN
10nF
3.3μF
1μF
BOOST
0.1μF 6.8μH
LT3592
SW
CMMSHI-40
DA
CAP
SHDN
OFF ON
BRIGHT
BRAKE
OUT
+
200/20mV
–
4.7μF
0.4Ω
51k
RT
GND
48.7k
2.2MHz
VFB
LUXEON
LXK2-PD12-S00
10k
3592 TA03
5V Supply with 500mA Current Limit
VIN
8V TO 32V
VIN
BOOST
1μF
0.1μF 6.8μH
SW
LT3592
ON
MBRA140
SHDN
DA
CAP
BRIGHT
OUT
4.7μF
0.4Ω
5V
31.6k
RT
48.7k
2.2MHz
GND
VFB
10k
3592 TA04
3592fc
21
LT3592
PACKAGE DESCRIPTION
DDB Package
10-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1722 Rev Ø)
0.64 ±0.05
(2 SIDES)
3.00 ±0.10
(2 SIDES)
R = 0.05
TYP
R = 0.115
TYP
6
0.40 ± 0.10
10
0.70 ±0.05
2.55 ±0.05
1.15 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
2.39 ±0.05
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
2.00 ±0.10
(2 SIDES)
0.75 ±0.05
0.64 ± 0.05
(2 SIDES)
5
0.25 ± 0.05
0 – 0.05
PIN 1
R = 0.20 OR
0.25 × 45°
CHAMFER
1
(DDB10) DFN 0905 REV Ø
0.50 BSC
2.39 ±0.05
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229
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
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
3592fc
22
LT3592
PACKAGE DESCRIPTION
MSE Package
10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1664)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.794 p 0.102
(.110 p .004)
5.23
(.206)
MIN
0.889 p 0.127
(.035 p .005)
1
0.05 REF
10
DETAIL “B”
CORNER TAIL IS PART OF
DETAIL “B” THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
NO MEASUREMENT PURPOSE
3.00 p 0.102
(.118 p .004)
(NOTE 3)
10 9 8 7 6
DETAIL “A”
0o – 6o TYP
1 2 3 4 5
GAUGE PLANE
0.53 p 0.152
(.021 p .006)
DETAIL “A”
0.18
(.007)
0.497 p 0.076
(.0196 p .003)
REF
3.00 p 0.102
(.118 p .004)
(NOTE 4)
4.90 p 0.152
(.193 p .006)
0.254
(.010)
0.29
REF
1.83 p 0.102
(.072 p .004)
2.083 p 0.102 3.20 – 3.45
(.082 p .004) (.126 – .136)
0.50
0.305 p 0.038
(.0197)
(.0120 p .0015)
BSC
TYP
RECOMMENDED SOLDER PAD LAYOUT
2.06 p 0.102
(.081 p .004)
SEATING
PLANE
0.86
(.034)
REF
1.10
(.043)
MAX
0.17 – 0.27
(.007 – .011)
TYP
0.50
(.0197)
BSC
0.1016 p 0.0508
(.004 p .002)
MSOP (MSE) 0908 REV C
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
3592fc
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
LT3592
TYPICAL APPLICATIONS
Five White LED Driver with External Booste Diode
VIN
24V TO 36V
VIN
1μF
BOOST
0.1μF 33μH
LT3592
BAS40
SW
MBRA140
DA
CAP
OFF ON
SHDN
BRIGHT
BRIGHT
0.4Ω
158k
RT
140k
900kHz
4.7μF
OUT
GND
VFB
10k
WHITE LEDs
3592 TA05
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
LT1932
Constant Current, 1.2MHz, High Efﬁciency White LED Boost
Regulator
VIN(MIN) = 1V, VIN(MAX) = 10V, VOUT(MAX) = 34V, Dimming Analog/PWM,
ISD < 1μA, ThinSOT™ Package
LT3465/
LT3465A
Constant Current, 1.2MHz/2.7MHz, High Efﬁciency White LED VIN(MIN) = 2.7V, VIN(MAX) = 16V, VOUT(MAX) = 34V, Dimming Analog/PWM,
ISD < 1μA, ThinSOT Package
Boost Regulator with Integrated Schottky Diode
LT3466/
LT3466-1
Dual Constant Current, 2MHz, High Efﬁciency White LED
Boost Regulator with Integrated Schottky Diode
VIN(MIN) = 2.7V, VIN(MAX) = 24V, VOUT(MAX) = 40V, Dimming 5mA,
ISD < 16μA, 3mm × 3mm DFN-10 Package
LT3474/
LT3474-1
36V, 1A (ILED), 2MHz,Step-Down LED Driver
VIN(MIN) = 4V, VIN(MAX) = 36V, VOUT(MAX) = 13.5V, Dimming 400:1 True
Color PWM, ISD < 1μA, TSSOP-16E Package
LT3475/
LT3475-1
Dual 1.5A(ILED), 36V, 2MHz,Step-Down LED Driver
VIN(MIN) = 4V, VIN(MAX) = 36V, VOUT(MAX) = 13.5V, Dimming 3,000:1 True
Color PWM, ISD < 1μA, TSSOP-20E Package
LT3476
Quad Output 1.5A, 2MHz High Current LED Driver with
1,000:1 Dimming
VIN(MIN) = 2.8V, VIN(MAX) = 16V, VOUT(MAX) = 36V, Dimming 1,000:1 True
Color PWM, ISD < 10μA, 5mm × 7mm QFN-10 Package
LT3478/
LT3478-1
4.5A, 2MHz High Current LED Driver with 3,000:1 Dimming
VIN(MIN) = 2.8V, VIN(MAX) = 36V, VOUT(MAX) = 40V, Dimming 1,000:1 True
Color PWM, ISD < 10μA, 5mm × 7mm QFN-10 Package
LT3486
Dual 1.3A , 2MHz High Current LED Driver
VIN(MIN) = 2.5V, VIN(MAX) = 24V, VOUT(MAX) = 36V, Dimming 1,000:1 True
Color PWM, ISD < 1μA, 5mm × 3mm DFN, TSSOP-16E Package
LT3491
Constant Current, 2.3MHz, High Efﬁciency White LED Boost
Regulator with Integrated Schottky Diode
VIN(MIN) = 2.5V, VIN(MAX) = 12V, VOUT(MAX) = 27V, Dimming 300:1 True
Color PWM, ISD < 8μA, 2mm × 2mm DFN-6, SC70 Package
LT3496
Triple Output 750mA, 2.1MHz High Current LED Driver with
3,000:1 Dimming
VIN(MIN) = 3V, VIN(MAX) = 30V, VOUT(MAX) = 40V, Dimming 3,000:1 True
Color PWM, ISD < 1μA, 4mm × 5mm QFN-28 Package
LT3497
Dual 2.3MHz, Full Function LED Driver with Integrated
Schottkys and 250:1 True Color PWM Dimming
VIN(MIN) = 2.5V, VIN(MAX) = 10V, VOUT(MAX) = 32V, Dimming 250:1 True
Color PWM, ISD < 12μA, 2mm × 3mm DFN-10 Package
LT3498
20mA LED Driver and OLED Driver Integrated Schottkys
VIN(MIN) = 2.5V, VIN(MAX) = 12V, VOUT(MAX) = 32V, Dimming Analog/PWM,
ISD < 8.5μA, 2mm × 3mm DFN-10 Package
LT3517
1.3A, 2.5MHz High Current LED Driver with 3,000:1 Dimming VIN(MIN) = 3V, VIN(MAX) = 30V, Dimming 3,000:1 True Color PWM,
ISD < 1μA, 4mm × 4mm QFN-16 Package
LT3518
2.3A, 2.5MHz High Current LED Driver with 3,000:1 Dimming VIN(MIN) = 3V, VIN(MAX) = 30V, Dimming 3,000:1 True Color PWM,
ISD < 1μA, 4mm × 4mm QFN-16 Package
LT3590
48V, 850kHz, 50mA Step-Down LED Driver
LT3591
Constant Current, 1MHz, High Efﬁciency White LED Boost
VIN(MIN) = 2.5V, VIN(MAX) = 12V, VOUT(MAX) = 40V, Dimming 80:1 True
Regulator with Integrated Schottky Diode and 80:1 True Color Color PWM, ISD < 9μA, 3mm × 2mm DFN-8 Package
PWM Dimming
VIN(MIN) = 4.5V, VIN(MAX) = 50V, Dimming 0.4, ISD < 15μA, 2mm × 2mm
DFN-6, SC70 Package
ThinSOT is a trademark of Linear Technology Corporation.
3592fc
24 Linear Technology Corporation
LT 0409 REV C • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2008

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