LT3496
Triple Output LED Driver
Features
Description
True Color PWM™ Dimming Delivers Up to 3000:1
Dimming Ratio
n Built-In Gate Driver for PMOS LED Disconnect
n Three Independent Driver Channels with 750mA,
45V Internal Switches
n Operates in Buck, Boost, Buck-Boost Modes
n CTRL Pin Accurately Sets LED Current Sense
Threshold Over a Range of 10mV to 100mV
n Adjustable Frequency: 330kHz to 2.1MHz
n Open LED Protection
n Wide V Supply Range:
IN
Operation from 3V to 30V
Transient Protection to 40V
n Surface Mount Components
n 28-Lead (4mm × 5mm) QFN and TSSOP Packages
The LT®3496 is a triple output DC/DC converter designed
to operate as a constant-current source and is ideal for
driving LEDs. The LT3496 works in buck, boost or buckboost mode. The LT3496 uses a fixed frequency, current
mode architecture resulting in stable operation over a
wide range of supply and output voltages. A frequency
adjust pin allows the user to program switching frequency
between 330kHz and 2.1MHz to optimize efficiency and
external component size.
n
The LT3496 supports 3000:1 dimming control on each
channel. Each of the three regulators is independently
operated by that channel’s PWM signal. The PWM feature
allows precise adjustment of the color mixing or dimming
ratio of the LED source. Each of the three channels has
a built-in gate driver to drive an external LED-disconnect
P-channel MOSFET, allowing high dimming range. The
output current range of each channel of the LT3496 is
programmed with an external sense resistor.
Applications
n
n
n
n
RGB Lighting
Billboards and Large Displays
Automotive and Avionic Lighting
Constant-Current Sources
The CTRL pins are used to adjust the LED currents either
for analog dimming or overtemperature protection.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
ThinSOT and True Color PWM are trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents, including
7199560, 7321203, and others pending.
Typical Application
High Dimming Ratio Triple Output LED Power Supply
PVIN
42V
CAP1
CAP2
CAP3
200mΩ
200mΩ
200mΩ
LED1
LED2
LED3
TG1
0.5A
18µH
0.47µF 0.47µF
SW1
VIN
3V TO 24V
1µF
PWM1, PWM2, PWM3
SHDN
CAP1, CAP2, CAP3
LED1, LED2, LED3
VIN
PWM1, PWM2, PWM3
SHDN
3000:1 PWM Dimming at 120Hz
TG3
TG2
7 LEDs
1µF
s3
0.5A
18µH
SW2
LT3496
GND
PWM
5V/DIV
0.5A
18µH
IL
0.5A/DIV
ILED
0.5A/DIV
0.47µF
0.5µs/DIV
SW3
TG1, TG2, TG3
VC1, VC2, VC3
VREF
CTRL1, CTRL2, CTRL3
fADJ
OVP1, OVP2, OVP3
3496 TA01b
22k
470pF
3496 TA01a
3496ff
LT3496
Absolute Maximum Ratings
(Note 1)
VIN (Note 4)................................................................40V
SW1, SW2, SW3, LED1, LED2, LED3,
CAP1, CAP2, CAP3....................................................45V
TG1, TG2, TG3..................................... CAP – 10V to CAP
PWM1, PWM2, PWM3...............................................20V
VREF , CTRL1, CTRL2, CTRL3, fADJ, VC1, VC2, VC3,
OVP1, OVP2, OVP3...................................................2.5V
SHDN (Note 4)............................................................VIN
Operating Junction Temperature Range (Notes 2, 6)
LT3496E............................................. –40°C to 125°C
LT3496I.............................................. –40°C to 125°C
LT3496H............................................. –40°C to 150°C
Storage Temperature Range
QFN..................................................... –65°C to 150°C
TSSOP.................................................. 65°C to 125°C
Lead Temperature (Soldering, 10 sec)
TSSOP............................................................... 300°C
Pin Configuration
TOP VIEW
TOP VIEW
26 LED3
PWM1
4
25 CAP3
VREF
5
24 SW3
CTRL3
6
CTRL2
7
CTRL1
8
fADJ
9
20 TG2
fADJ 6
VC3 10
19 SW1
VC3 7
16 SW1
VC2 11
18 CAP1
VC2 8
15 CAP1
VC1 12
17 LED1
28 27 26 25 24 23
PWM1 1
22 CAP3
21 SW3
23 SW2
VREF 2
CTRL3 3
20 SW2
22 CAP2
CTRL2 4
21 LED2
CTRL1 5
FE PACKAGE
28-LEAD PLASTIC TSSOP
θJA = 30°C/W, θJC = 10°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
LED1
TG1
OVP1
15 OVP1
9 10 11 12 13 14
OVP2
16 TG1
OVP2 14
18 LED2
17 TG2
VC1
OVP3 13
19 CAP2
29
OVP3
29
LED3
27 TG3
3
TG3
2
PWM2
VIN
PWM3
SHDN
28 VIN
PWM3
1
PWM2
SHDN
UFD PACKAGE
28-LEAD (4mm s 5mm) PLASTIC QFN
θJA = 34°C/W, θJC = 2.7°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
Order Information
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3496EFE#PBF
LT3496EFE#TRPBF
3496FE
28-Lead Plastic TSSOP
–40°C to 125°C
LT3496IFE#PBF
LT3496IFE#TRPBF
3496FE
28-Lead Plastic TSSOP
–40°C to 125°C
LT3496EUFD#PBF
LT3496EUFD#TRPBF
3496
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
LT3496IUFD#PBF
LT3496IUFD#TRPBF
3496
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
LT3496HUFD#PBF
LT3496HUFD#TRPBF
3496
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 150°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
*For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
3496ff
LT3496
Electrical
Characteristics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 5V, VSHDN = 5V, CAP1, CAP2, CAP3 = 5V, PWM1, PWM2, PWM3 = 5V,
fADJ = 0.5V, CTRL1, CTRL2, CTRL3 = 1.5V, OVP1, OVP2, OVP3 = 0V, unless otherwise noted.
PARAMETER
CONDITIONS
VIN Operation Voltage
(Note 4)
MIN
VIN Undervoltage Lockout
Full-Scale LED Current Sense Voltage
(VCAP1-LED1, VCAP2-LED2, VCAP3-LED3)
CAP1, CAP2, CAP3 = 24V
One-Tenth Scale LED Current Sense Voltage
(VCAP1-LED1, VCAP2-LED2, VCAP3-LED3)
CTRL1, CTRL2, CTRL3 = 100mV, CAP1, CAP2, CAP3 = 24V
H-Grade
E-Grade, I-Grade
CAP1, CAP2, CAP3 Operating Voltage
0V ≤ VCAP1-LED1 ≤ 104mV
0V ≤ VCAP2-LED2 ≤ 104mV
0V ≤ VCAP3-LED3 ≤ 104mV
VREF Output Voltage
IREF = 200µA, Current Out of Pin
VREF Line Regulation
3V ≤ VIN ≤ 40V, IREF = 10µA
Quiescent Current in Shutdown
SHDN = 0V
Quiescent Current Idle
PWM1, PWM2, PWM3 = 0V
TYP
3
MAX
UNITS
30
V
2.1
2.4
V
98
97
100
l
103
104
mV
mV
l
l
7.5
7.5
10
10
13.5
12.5
mV
mV
2.5
l
1.96
Quiescent Current Active (Not Switching)
45
V
2.04
V
0.03
%/V
0.1
10
µA
6
7.5
mA
2
11
14
mA
1900
2100
1300
330
2300
kHz
kHz
kHz
70
78
87
97
Switching Frequency
fADJ = 1.5V
fADJ = 0.5V
fADJ = 0.1V
Maximum Duty Cycle
fADJ = 1.5V (2.1MHz)
fADJ = 0.5V (1.3MHz)
fADJ = 0.1V (330kHz)
CTRL1, CTRL2, CTRL3 Input Bias Current
Current Out of Pin, CTRL1, CTRL2, CTRL3 = 0.1V
20
100
nA
fADJ Input Bias Current
Current Out of Pin, fADJ = 0.1V
20
100
nA
OVP1, OVP2, OVP3 Input Bias Current
Current Out of Pin, OVP1, OVP2, OVP3 = 0.1V
10
100
nA
0.95
1
1.05
V
–20
0
20
nA
OVP1, OVP2, OVP3 Threshold
l
%
%
%
VC1, VC2, VC3 Idle Input Bias Current
PWM1, PWM2, PWM3 = 0V
VC1, VC2, VC3 Output Impedance
CAP1, CAP2, CAP3 = 24V
10
MΩ
EAMP gm (ΔIVC/ΔVCAP-LED)
CAP1, CAP2, CAP3 = 24V
200
µS
SW1, SW2, SW3 Current Limit
(Note 3)
SW1, SW2, SW3 VCESAT
ISW = 500mA (Note 3)
SW1, SW2, SW3 Leakage Current
SHDN = 0V, SW = 5V
CAP1, CAP2, CAP3 Input Bias Current
750
1000
1250
260
mV
2
180
mA
µA
250
µA
CAP1, CAP2, CAP3, LED1, LED2, LED3 Idle Input
Bias Current
PWM1, PWM2, PWM3 = 0V
1
µA
CAP1, CAP2, CAP3, LED1, LED2, LED3 Input Bias
Current in Shutdown
SHDN = 0V
1
µA
3496ff
LT3496
Electrical
Characteristics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 5V, VSHDN = 5V, CAP1, CAP2, CAP3 = 5V, PWM1, PWM2, PWM3 = 5V,
fADJ = 0.5V, CTRL1, CTRL2, CTRL3 = 1.5V, OVP1, OVP2, OVP3 = 0V, unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
SHDN Input Low Voltage
0.4
SHDN Input High Voltage
SHDN Pin Current
MAX
1.5
VSHDN = 5V, Current Into Pin
V
V
65
PWM1, PWM2, PWM3 Input Low Voltage
PWM1, PWM2, PWM3 Input High Voltage
UNITS
100
µA
0.4
V
1.2
V
PWM1, PWM2, PWM3 Pin Current
Current Into Pin
160
210
µA
Gate Off Voltage
(CAP1 – TG1, CAP2 – TG2, CAP3 – TG3)
CAP1, CAP2, CAP3 = 40V,
PWM1, PWM2, PWM3 = 0V
0.1
0.3
V
Gate On Voltage
(CAP1 – TG1, CAP2 – TG2, CAP3 – TG3)
CAP1, CAP2, CAP3 = 40V
6.5
7.5
V
Gate Turn-On Delay
CLOAD = 300pF, CAP1, CAP2, CAP3 = 40V (Note 5)
110
ns
Gate Turn-Off Delay
CLOAD = 300pF, CAP1, CAP2, CAP3 = 40V (Note 5)
110
ns
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 LT3496E 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
LT3496I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The LT3496H is guaranteed over the full –40°C to
150°C operating junction temperature range. High junction temperatures
degrade operating lifetimes. Operating lifetime is derated at junction
temperatures greater than 125°C.
5.5
Note 3: Current flows into pin. Current limit and switch VCESAT is
guaranteed by design and/or correlation to static test.
Note 4: Absolute maximum voltage at the VIN and SHDN pins is 40V for
nonrepetitive 1 second transients, and 30V for continuous operation.
Note 5: Gate turn-on/turn-off delay is measured from 50% level of PWM
voltage to 90% level of gate on/off voltage.
Note 6: The LT3496 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 operating above
the specified maximum operating junction temperature may impair device
reliability.
3496ff
LT3496
Typical Performance Characteristics
Quiescent Current
1000
10
400
800
8
PWM1, PWM2, PWM3 = 0V
6
4
SWITCH CURRENT LIMIT (mA)
SWITCH VOLTAGE (mV)
INPUT CURRENT (mA)
500
PWM1, PWM2, PWM3 = 5V
12
300
200
100
2
VC = GND, NOT SWITCHING
0
10
20
30
0
40
0
200
VIN (V)
600
800
400
SWITCH CURRENT (mA)
3496 G01
200
0
1000
800
2250
2.03
2000
2.02
1750
VREF (V)
2.00
3496 G04
1.96
–50 –25
100
1000
1.97
25 50 75 100 125 150
TEMPERATURE (°C)
80
1500
1.98
200
60
40
DUTY CYCLE (%)
1250
1.99
400
20
Switch Frequency vs fADJ
2.04
2.01
600
0
3496 G03
SWITCH FREQUENCY (kHz)
1000
0
400
Reference Voltage
vs Temperature
1200
0
–50 –25
600
3496 G02
Switch Current Limit vs
Temperature
CURRENT LIMIT (mA)
Switch Current Limit
vs Duty Cycle
Switch On Voltage
14
0
(TA = 25°C unless otherwise noted)
750
500
250
0
25 50 75 100 125 150
TEMPERATURE (°C)
3496 G05
0
0
0.2
0.4
0.6
fADJ (V)
0.8
1.0
1.2
3496 G06
3496ff
LT3496
Typical Performance Characteristics
Switch Frequency vs Temperature
120
fADJ = 1.2V
2.2
2.1
2.0
VCAP = 24V
1.8
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
80
60
40
0
0
101
100
99
0.2
0.4
0.6
0.8
CTRL (V)
1
1.2
97
0
10
20
30
VCAP (V)
40
50
3496 G09
3496 G08
VCAP-LED Threshold vs
Temperature
VCAP-LED THRESHOLD (mV)
CTRL = 1.2V
98
3496 G07
102
VCAP-LED Threshold vs VCAP
102
20
1.9
103
103
100
VCAP-LED THRESHOLD (mV)
SWITCH FREQUENCY (MHz)
2.3
VCAP-LED Threshold vs CTRL
VCAP-LED TRHESHOLD (mV)
2.4
(TA = 25°C unless otherwise noted)
PMOS Turn On Waveforms
PMOS Turn Off Waveforms
CTRL = 1.2V
VCAP = 24V
5V
5V
PWM
101
PWM
0V
0V
100
40V
99
TG
30V
98
97
–50 –25
40V
TG
0
25 50 75 100 125 150
TEMPERATURE (°C)
30V
VCAP = 40V
200ns/DIV
3496 G11
VCAP = 40V
200ns/DIV
3496 G12
3496 G10
3496ff
LT3496
Pin Functions
PWM1, PWM2, PWM3: Pulse Width Modulated Inputs.
Signal low turns off the respective converter, reduces
quiescent supply current and causes the VC pin for that
converter to become high impedance. PWM pin must not
be left floating; tie to VREF if not used.
When the PWM pin is low, the TG pin pulls up to CAP to
turn off the external MOSFET. When the PWM pin is high,
the external MOSFET turns on. Respective CAP-TG is
limited to 6.5V to protect the MOSFET. Leave open if the
external MOSFET is not used.
VREF: Reference Output Pin. Can supply up to 200µA. The
nominal Output Voltage is 2V.
LED1, LED2, LED3: Noninverting Inputs of Current Sense
Error Amplifiers. Connect directly to LED current sense
resistor terminal for current sensing of the respective
converter
CTRL1, CTRL2, CTRL3: LED Current Adjustment Pins. Sets
voltage across external sense resistor between CAP and
LED pins of the respective converter. Setting CTRL voltage
to be less than 1V will control the current sense voltage to
be one-tenth of CTRL voltage. If CTRL voltage is higher than
1V, the default current sense voltage is 100mV. The CTRL
pin must not be left floating.
fADJ: Switching Frequency Adjustment Pin. Setting fADJ
voltage to be less than 1V will adjust switching frequency
up to 2.1MHz. If fADJ voltage is higher than 1V, the default
switching frequency is 2.1MHz. The fADJ pin must not be
left floating.
VC1, VC2, VC3: Error Amplifier Compensation Pins. Connect a series RC from these pins to GND.
CAP1, CAP2, CAP3: Inverting Inputs of Current Sense Error
Amplifiers. Connect directly to other terminal of LED current
sense resistor terminal of the respective converter.
SW1, SW2, SW3: Switch Pins. Collector of the internal
NPN power switch of the respective converter. Connect
to external inductor and anode of external Schottky rectifier of the respective converter. Minimize the metal trace
area connected to this pin to minimize electromagnetic
interference.
VIN: Input Supply Pin. Must be locally bypassed. Powers
the internal control circuitry.
OVP1, OVP2, OVP3: Open LED Protection Pins. A voltage
higher than 1V on OVP turns off the internal main switch
of the respective converter. Tie to ground if not used.
SHDN: Shutdown Pin. Used to shut down the switching
regulator and the internal bias circuits for all three converters. Tie to 1.5V or greater to enable the device. Tie below
0.4V to turn off the device.
TG1, TG2, TG3: The Gate Driver Output Pins for Disconnnect P‑Channel MOSFETs. One for each converter.
Exposed Pad: Signal Ground and Power Ground. Solder
paddle directly to ground plane.
3496ff
LT3496
Block Diagram
D1
VSENSE
+
–
ILED
M1
C2
LED1
L1
VIN
C1
RSENSE 0.2Ω
CAP1
R3
LED1
TG1
OVP1
–
RC
+
V1
A1
–
+
+
–
1V
NPN
DRIVER
A6
A4
VC
A8
+
–
R1 2k
1V
CTRL1
EAMP
+
PWM1
CC
SW1
MOSFET
DRIVER
VC1
R4
PWM1
A7
Q3
SLOPE
Q1
SR LATCH
–
+
CTRL
BUFFER
A5
A3
R
A2
PWM
COMPARATOR
Q
S
ISENS2
+
A10
R2
20k
–
GND
REPLICATED FOR EACH CHANNEL
VIN
VIN
C3
SHDN
INTERNAL
REGULATOR
AND UVLO
VIN
ISRC
200µA
VREF
RAMP
GENERATOR
–
2V
REFERENCE
+
A9
Q2
OSCILLATOR
fADJ
SHARED COMPONENTS
R5
C4
3496 BD
R6
Figure 1. LT3496 Block Diagram Working in Boost Configuration
3496ff
LT3496
Applications Information
Operation
The LT3496 uses a fixed frequency, current mode control
scheme to provide excellent line and load regulation. Operation can be best understood by referring to the Block
Diagram in Figure 1. The oscillator, ramp generator, reference, internal regulator and UVLO are shared among the
three converters. The control circuitry, power switch etc.,
are replicated for each of the three converters. Figure 1
shows the shared circuits and only converter 1 circuits.
If the SHDN pin is tied to ground, the LT3496 is shut
down and draws minimal current from VIN. If the SHDN
pin exceeds 1.5V, the internal bias circuits turn on. The
switching regulators start to operate when their respective
PWM signal goes high.
The main control loop can be understood by following the
operation of converter 1. The start of each oscillator cycle
sets the SR latch, A3, and turns on power switch Q1. The
signal at the noninverting input (SLOPE node) of the PWM
comparator A2 is proportional to the sum of the switch
current and oscillator ramp. When SLOPE exceeds VC1
(the output of the error amplifier A1), A2 resets the latch
and turns off the power switch Q1 through A4 and A5.
In this manner, A10 and A2 set the correct peak current
level to keep the output in regulation. Amplifier A8 has
two noninverting inputs, one from the 1V internal voltage
reference and the other one from the CTRL1 pin. Whichever
input is lower takes precedence. A8, Q3 and R1 force V1,
the voltage across R1, to be one tenth of either 1V or the
voltage of CTRL1 pin, whichever is lower. VSENSE is the
voltage across the sensing resistor, RSENSE, which is connected in series with the LEDs. VSENSE is compared to V1
by A1. If VSENSE is higher than V1, the output of A1 will
decrease, thus reducing the amount of current delivered to
LEDs. In this manner the current sensing voltage VSENSE
is regulated to V1.
Converters 2 and 3 are identical to converter 1.
PWM Dimming Control
LED1 can be dimmed with pulse width modulation using the PWM1 pin and an external P-channel MOSFET,
M1. If the PWM1 pin is pulled high, M1 is turned on by
internal driver A7 and converter 1 operates nominally.
A7 limits CAP1-TG1 to 6.5V to protect the gate of M1. If
the PWM1 pin is pulled low, Q1 is turned off. Converter 1
stops operating, M1 is turned off, disconnects LED1 and
stops current draw from output capacitor C2. The VC1
pin is also disconnected from the internal circuitry and
draws minimal current from the compensation capacitor
CC. The VC1 pin and the output capacitor store the state
of the LED1 current until PWM1 is pulled up again. This
leads to a highly linear relationship between pulse width
and output light, and allows for a large and accurate dimming range. A P-channel MOSFET with smaller total gate
charge (QG) improves the dimming performance, since
it can be turned on and off faster. Use a MOSFET with a
QG lower than 10nC, and a minimum VTH of –1V to –2V.
Don’t use a Low VTH PMOS. To optimize the PWM control
of all the three channels, the rising edge of all the three
PWM signals should be synchronized.
In the applications where high dimming ratio is not required,
M1 can be omitted to reduce cost. In these conditions,
TG1 should be left open. The PWM dimming range can be
further increased by using CTRL1 pin to linearly adjust the
current sense threshold during the PWM1 high state.
Loop Compensation
Loop compensation determines the stability and transient
performance. The LT3496 uses current mode control to
regulate the output, which simplifies loop compensation.
To compensate the feedback loop of the LT3496, a series
resistor-capacitor network should be connected from the
VC pin to GND. For most applications, the compensation
capacitor should be in the range of 100pF to 1nF. The compensation resistor is usually in the range of 5k to 50k.
To obtain the best performance, tradeoffs should be made
in the compensation network design. A higher value of
compensation capacitor improves the stability and dimming range (a larger capacitance helps hold the VC voltage
when the PWM signal is low). However, a large compensation capacitor also increases the start-up time and the
time to recover from a fault condition. Similarly, a larger
compensation resistor improves the transient response
but may reduce the phase margin. A practical approach
is to start with one of the circuits in this data sheet that
is similar to your application and tune the compensation
network to optimize the performance. The stability, PWM
3496ff
LT3496
Applications Information
dimming waveforms and the start-up time should be
checked across all operating conditions.
Open-LED Protection
Input Capacitor Selection
For proper operation, it is necessary to place a bypass
capacitor to GND close to the VIN pin of the LT3496. A
1µF or greater capacitor with low ESR should be used. A
ceramic capacitor is usually the best choice.
The LT3496 has open-LED protection for all the three
converters. As shown in Figure 1, the OVP1 pin receives
the output voltage (the voltage across the output capacitor)
feedback signal from an external resistor divider. OVP1
voltage is compared with a 1V internal voltage reference by
comparator A6. In the event the LED string is disconnected
or fails open, converter 1 output voltage will increase, causing OVP1 voltage to increase. When OVP1 voltage exceeds
1V, the power switch Q1 will turn off, and cause the output
voltage to decrease. Eventually, OVP1 will be regulated to
1V and the output voltage will be limited. In the event one
of the converters has an open-LED protection, the other
converters will continue functioning properly.
where D is the switch duty cycle. A 1µF ceramic type capacitor placed close to the Schottky diode and the ground
plane is usually sufficient for each channel.
Switching Frequency and Soft-Start
Output Capacitor Selection
The LT3496 switching frequency is controlled by fADJ pin
voltage. Setting fADJ voltage to be less than 1V will reduce
switching frequency.
If fADJ voltage is higher than 1V, the default switching
frequency is 2.1MHz. In general, a lower switching frequency should be used where either very high or very
low switch duty cycle is required or higher efficiency is
desired. Selection of a higher switching frequency will
allow use of low value external components and yield a
smaller solution size and profile.
Connecting fADJ pin to a lowpass filter (R5 and C4 in
Figure 1) from the REF pin provides a soft-start function.
During start-up, fADJ voltage increases slowly from 0V to
the setting voltage. As a result, the switching frequency
increases slowly to the setting frequency. This function
limits the inrush current during start-up.
Undervoltage Lockout
The LT3496 has an undervoltage lockout circuit that
shuts down all the three converters when the input voltage drops below 2.4V. This prevents the converter from
switching in an erratic mode when powered from a low
supply voltage.
In the buck mode configuration, the capacitor at PVIN has
large pulsed currents due to the current returned though
the Schottky diode when the switch is off. For the best
reliability, this capacitor should have low ESR and ESL
and have an adequate ripple current rating. The RMS
input current is:
IIN(RMS) =ILED •
(1– D) • D
The selection of output filter capacitor depends on the load
and converter configuration, i.e., step-up or step-down.
For LED applications, the equivalent resistance of the LED
is typically low, and the output filter capacitor should be
large enough to attenuate the current ripple.
To achieve the same LED ripple current, the required filter
capacitor value is larger in the boost and buck-boost mode
applications than that in the buck mode applications. For the
LED buck mode applications, a 0.22µF ceramic capacitor
is usually sufficient for each channel. For the LED boost
and buck-boost applications, a 1µF ceramic capacitor is
usually sufficient for each channel. If higher LED current
ripple can be tolerated, a lower output capacitance can be
selected to reduce the capacitor’s cost and size.
Use only ceramic capacitors with X7R or X5R dielectric,
as they are good for temperature and DC bias stability of
the capacitor value. All ceramic capacitors exhibit loss of
capacitance value with increasing DC voltage bias, so it
may be necessary to choose a higher value capacitor to get
the required capacitance at the operation voltage. Always
check that the voltage rating of the capacitor is sufficient.
Table 1 shows some recommended capacitor vendors.
3496ff
10
LT3496
Applications Information
Table 2. Surface Mount Inductors
Table 1. Ceramic Capacitor Manufacturers
VENDOR
TYPE
SERIES
Taiyo Yuden
Ceramic
X5R, X7R
AVX
Ceramic
X5R, X7R
Murata
Ceramic
X5R, X7R
Kemet
Ceramic
X5R, X7R
VALUE
(µH)
DCR
(Ω MAX)
IRMS (A)
SIZE
W × L × H (mm3)
CMD4D06
2.2
0.116
0.95
3.5 × 4.3 × 0.8
3.3
0.174
0.77
CDRH3D16
2.2
0.072
1.20
3.3
0.085
1.10
4.7
0.105
0.90
CDRH4D28
10
0.128
1.00
15
0.149
0.76
CDRH5D28
22
0.122
0.9
33
0.189
0.75
2.2
0.140
0.97
3.3
0.165
0.90
4.7
0.246
0.74
SD14
10
0.2058
1.1
5.0 × 5.0 × 1.4
SD20
15
0.1655
1.25
5.0 × 5.0 × 2.0
22
0.2053
1.12
33
0.2149
1.11
5.0 × 5.0 × 2.5
2.2
0.06
1.48
3.0 × 3.0 × 1.5
4.7
0.12
1.02
4.7
0.075
1.6
10
0.100
1.2
15
0.180
0.95
22
0.210
0.77
PART NUMBER
Sumida
Inductor Selection
Several inductors that work well with the LT3496 are listed
in Table 2. However, there are many other manufacturers
and devices that can be used. Consult each manufacturer
for more detailed information and their entire range of
parts. Ferrite core inductors should be used to obtain the
best efficiency. Choose an inductor that can handle the
necessary peak current without saturating, and ensure that
the inductor has a low DCR (copper-wire resistance) to
minimize I2R power losses. An inductor with a magnetic
shield should be used to prevent noise radiation and cross
coupling among the three channels.
SD3112
SD25
The Schottky diode conducts current during the interval
when the switch is turned off. Select a diode VR rated
for the maximum SW voltage. It is not necessary that
the forward current rating of the diode equal the switch
current limit. The average current, IF , through the diode
is a function of the switch duty cycle. Select a diode with
forward current rating of:
Taiyo Yuden
where IL is the inductor current.
If using the PWM feature for dimming, it is important to
consider diode leakage, which increases with the temperature from the output during the PWM low interval.
Therefore, choose the Schottky diode with sufficient low
leakage current. Table 3 shows several Schottky diodes
that work well with the LT3496.
5.0 × 5.0 × 3.0
6.0 × 6.0 × 3.0
CooperET
Diode Selection
IF = IL • (1 – D)
3.8 × 3.8 × 1.8
NR3015
NP04SZB
3.1 × 3.1 × 1.2
4.0 × 4.0 × 1.8
Table 3. Schottky Diodes
PART NUMBER
VR (V)
IF (A)
PACKAGE
ZLLS350
40
0.38
SOD523
ZLLS400
40
0.52
SOD323
ZETEX
3496ff
11
LT3496
Applications Information
Programming the LED Current
The LED current of each channel is programmed by connecting an external sense resistor RSENSE in series with
the LED load, and setting the voltage regulation threshold
across that sense resistor using CTRL input. If the CTRL
voltage, VCTRL, is less than 1V, the LED current is:
ILED =
VCTRL
10 • RSENSE
Board Layout
If VCTRL is higher than 1V, the LED current is:
ILED =
100mV
RSENSE
The CTRL pins should not be left open. The CTRL pin
can also be used in conjunction with a PTC thermistor to
provide overtemperature protection for the LED load as
shown in Figure 2.
2V
VREF
voltages to ensure that a junction temperature of 125°C
is not exceeded. This is especially important when operating at high ambient temperatures. The exposed pad on
the bottom of the package must be soldered to a ground
plane. This ground should then be connected to an internal
copper ground plane with thermal vias placed directly
under the package to spread out the heat dissipated by
the LT3496.
45k
50k
CTRL1 to CTRL3
5k
PTC
3496 F02
Figure 2
Thermal Considerations
The LT3496 is rated to a maximum input voltage of 30V
for continuous operation, and 40V for nonrepetitive one
second transients. Careful attention must be paid to the
internal power dissipation of the LT3496 at higher input
The high speed operation of the LT3496 demands careful
attention to board layout and component placement. The
exposed pad of the package is the only GND terminal of
the IC and is important for thermal management of the
IC. Therefore, it is crucial to achieve a good electrical
and thermal contact between the exposed pad and the
ground plane of the board. Also, in boost configuration,
the Schottky rectifier and the capacitor between GND and
the cathode of the Schottky are in the high frequency
switching path where current flow is discontinuous. These
elements should be placed so as to minimize the path
between SW and the GND of the IC. To reduce electromagnetic interference (EMI), it is important to minimize
the area of the SW node. Use the GND plane under SW
to minimize interplane coupling to sensitive signals. To
obtain good current regulation accuracy and eliminate
sources of channel to channel coupling, the CAP and LED
inputs of each channel of the LT3496 should be run as
separate lines back to the terminals of the sense resistor.
Any resistance in series with CAP and LED inputs should
be minimized. Finally, the bypass capacitor on the VIN supply to the LT3496 should be placed as close as possible
to the VIN terminal of the device.
3496ff
12
LT3496
Typical Applications
Minimum BOM Buck Mode LED Driver
PVIN
42V
CAP1
CAP2
CAP3
330mΩ
330mΩ
330mΩ
LED1
LED2
LED3
0.3A
0.3A
0.3A
7 LEDs
C6
0.22µF
C4
C5
0.22µF 0.22µF
L1
15µH
D1
SW1
VIN
3V
C7
1µF
PWM1, PWM2, PWM3
SHDN
CAP1, CAP2, CAP3
LED1, LED2, LED3
VIN
PWM1, PWM2, PWM3
SHDN
D2
C1-C3
1µF
s3
L2
15µH
SW2
LT3496
GND
L3
15µH
D3
SW3
TG1, TG2, TG3
VC1, VC2, VC3
VREF
CTRL1, CTRL2, CTRL3
fADJ
OVP1, OVP2, OVP3
OPEN
22k
470pF
3496 TA07a
C1-C3, C7: MURATA GRM31MR71H105KA88
C4-C6: MURATA GRM21BR71H224KA01
D1-D3: DIODES DFLS160
L1-L3: TAIYO YUDEN NP04SZB 150M
300:1 PWM Dimming at 120Hz
Efficiency
100
PWM
5V/DIV
PWM = 3V
CTRL = 0V TO 1.2V
95
EFFICIENCY (%)
IL
0.5A/DIV
ILED
0.5A/DIV
5µs/DIV
3496 TA07b
90
85
80
75
0
50
100
150
200
ILED (mA)
250
300
3496 TA07c
3496ff
13
LT3496
TYPICAL APPLICATIONS
Triple Boost 100mA × 10 LED Driver
PVIN
12V
C1
2.2µF
L1
10µH
L2
10µH
D1
D2
CAP1
C2
1µF
L3
10µH
C3
1µF
1Ω
TG2
OVP1
20k
SW1
VIN
3V
C5
1µF
PWM1, PWM2, PWM3
SHDN
1Ω
LED3
TG3
M2
825k
100mA
CAP3
LED2
M1
10 LEDs
C4
1µF
1Ω
LED1
TG1
D3
CAP2
825k
10 LEDs
100mA
OVP2
20k
SW2
CAP1, CAP2, CAP3
LED1, LED2, LED3
VIN
PWM1, PWM2, PWM3
SHDN
M3
825k
10 LEDs
OVP3
100mA
20k
SW3
TG1, TG2, TG3
OVP1, OVP2, OVP3
VC1, VC2, VC3
VREF
fADJ
CTRL1, CTRL2, CTRL3
LT3496
GND
10k
470pF
3496 TA03a
C1: MURATA GRM31MR71C225KA35
C2-C5: MURATA GRM31MR71H105KA88
D1-D3: DIODES DFLS160
L1-L3: TAIYO YUDEN NP04SZB 100M
M1-M3: ZETEX ZXMP6A13F
Efficiency vs PWM Duty Cycle
3000:1 PWM Dimming at 120Hz
95
CTRL = 2V
90
PWM
5V/DIV
EFFICIENCY (%)
85
IL
0.5A/DIV
ILED
0.1A/DIV
80
75
70
65
60
55
0.5µs/DIV
3496 TA03b
50
0
20
80
60
40
PWM DUTY CYCLE (%)
100
3496 TA03d
3496ff
14
LT3496
TYPICAL APPLICATIONS
Dual Boost LED Driver
PVIN
12V
C1
2.2µF
L1
10µH
L2
10µH
L3
10µH
D1
D2
CAP1
C2
1µF
C3
1µF
1Ω
D3
CAP2
LED1
CAP3
C4
1µF
1Ω
1Ω
LED2
LED3
M1
M2
825k
10 LEDs
PWM
SHDN
10 LEDs
20k
SW1 TG1
VIN
3V TO 12V
C5
1µF
825k
OVP1
100mA
SW2
CAP1, CAP2, CAP3
LED1, LED2, LED3
VIN
PWM1, PWM2, PWM3
SHDN
SW3 TG2
OVP1, OVP2, OVP3
TG3
VC1, VC2, VC3
VREF
fADJ
CTRL1, CTRL2, CTRL3
LT3496
GND
OVP2-3
200mA
20k
OPEN
10k
470pF
3496 TA04
C1: MURATA GRM31MR71C225KA35
C2-C5: MURATA GRM31MR71H105KA88
D1-D3: DIODES DFLS160
L1-L3: TAIYO YUDEN NP04SZB 100M
M1, M2: ZETEX ZXMP6A13F
Triple Boost 20mA × 8 LED Driver
PVIN
5V
C1
2.2µF
L1
22µH
L2
22µH
D1
C2
1µF
L3
22µH
D2
CAP1
C3
1µF
5Ω
TG2
M1
20mA
PWM1, PWM2, PWM3
SHDN
8 LEDs
20k
CAP1, CAP2, CAP3
LED1, LED2, LED3
VIN
PWM1, PWM2, PWM3
SHDN
C1: MURATA GRM31MR71C225KA35
C2-C5: MURATA GRM31MR71H105KA88
D1-D3: ZETEX ZLLS350
L1-L3: TAIYO YUDEN NP04SZB 220M
M1-M3: ZETEX ZXMP6A13F
LED3
TG3
M2
M3
825k
OVP1
SW1
VIN
5V
C5
1µF
5Ω
LED2
825k
8 LEDs
CAP3
C4
1µF
5Ω
LED1
TG1
D3
CAP2
SW2
LT3496
GND
20mA
825k
OVP2
8 LEDs
20k
20mA
OVP3
20k
SW3
TG1, TG2, TG3
OVP1, OVP2, OVP3
VC1, VC2, VC3
VREF
CTRL1, CTRL2, CTRL3
82k
10k
470pF
fADJ
20k
3496 TA08a
3496ff
15
LT3496
TYPICAL APPLICATIONS
Buck-Boost Mode 300mA × 6 LED Driver
PVIN
10V TO 16V
C1
2.2µF
6 LEDs
300mA
L1
10µH
L2
10µH
L3
10µH
825k
M1
LED1
LED2
1Ω
1Ω
CAP1
D1
C3
1µF
CAP3
D3
C4
0.1µF
C5
1µF
C7
1µF
PVIN
SW3 TG1
SW2
CAP1, CAP2, CAP3
LED1, LED2, LED3
VIN
PWM1, PWM2, PWM3
SHDN
PWM
SHDN
C8
1µF
C6
0.1µF
PVIN
PVIN
SW1
VIN
3V TO 16V
1Ω
CAP2
D2
C2
0.1µF
OVP1-3
20k
LED3
OVP1, OVP2, OVP3
TG1, TG2, TG3
VC1, VC2, VC3
VREF
fADJ
CTRL1, CTRL2, CTRL3
LT3496
GND
OPEN
10k
470pF
3496 TA05
C1: MURATA GRM31MR71E225KA93
C2, C4, C6: MURATA GRM21BR71H104KA01B
C3, C5, C7: MURATA GRM31MR71H105KA88
C8: MURATA GRM31MR71E105KA93
D1-D3: DIODES DFLS160
L1-L3: TAIYO YUDEN NP04SZB 100M
M1: ZETEX ZXMP6A13F
Triple Buck Mode LED Driver with Open LED Protection
PVIN
12V TO 40V
TG1
CAP1
CAP2
CAP3
200mΩ
200mΩ
200mΩ
LED1
LED2
LED3
TG2
M1
M2
20k
0.5A
C4
0.47µF
5.6k
M4
OVP1
2k
L1
10µH
D1
SW1
VIN
3V TO 24V
C7
1µF
PWM1, PWM2, PWM3
SHDN
20k
0.5A
C5
0.47µF
D2
TG3
M3
20k
5.6k
L2
10µH
0.5A
M5
C1-C3, C7: MURATA GRM31MR71H105KA88
C4-C6: MURATA GRM188R71C474KA88
D1-D3: DIODES DFLS160
L1-L3: TAIYO YUDEN NP04SZB 100M
M1-M3: ZETEX ZXMP6A13F
M4-M6: PHILIPS BC858B
5.6k
M6
OVP2 OVP1
2k
SW2
CAP1, CAP2, CAP3
LED1, LED2, LED3
VIN
PWM1, PWM2, PWM3
SHDN
C1-C3
1µF
s3
LT3496
GND
2k
L3
10µH
C6
0.47µF
D3
SW3
TG1, TG2, TG3
OVP1, OVP2, OVP3
VC1, VC2, VC3
VREF
fADJ
CTRL1, CTRL2, CTRL3
22k
470pF
3496 TA02
3496ff
16
LT3496
Package Description
FE Package
28-Lead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1663)
exposed pad Variation EB
9.60 – 9.80*
(.378 – .386)
4.75
(.187)
4.75
(.187)
28 2726 25 24 23 22 21 20 19 18 1716 15
6.60 p0.10
2.74
(.108)
4.50 p0.10
SEE NOTE 4
0.45 p0.05
EXPOSED
PAD HEAT SINK
ON BOTTOM OF
PACKAGE
6.40
2.74
(.252)
(.108)
BSC
1.05 p0.10
0.65 BSC
RECOMMENDED SOLDER PAD LAYOUT
4.30 – 4.50*
(.169 – .177)
0.09 – 0.20
(.0035 – .0079)
0.50 – 0.75
(.020 – .030)
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
2. DIMENSIONS ARE IN MILLIMETERS
(INCHES)
3. DRAWING NOT TO SCALE
1 2 3 4 5 6 7 8 9 10 11 12 13 14
0.25
REF
1.20
(.047)
MAX
0o – 8o
0.65
(.0256)
BSC
0.195 – 0.30
(.0077 – .0118)
TYP
0.05 – 0.15
(.002 – .006)
FE28 (EB) TSSOP 0204
4. RECOMMENDED MINIMUM PCB METAL SIZE
FOR EXPOSED PAD ATTACHMENT
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.150mm (.006") PER SIDE
3496ff
17
LT3496
Package Description
UFD Package
28-Lead Plastic QFN (4mm × 5mm)
(Reference LTC DWG # 05-08-1712 Rev B)
0.70 p0.05
4.50 p 0.05
3.10 p 0.05
2.50 REF
2.65 p 0.05
3.65 p 0.05
PACKAGE OUTLINE
0.25 p0.05
0.50 BSC
3.50 REF
4.10 p 0.05
5.50 p 0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
4.00 p 0.10
(2 SIDES)
0.75 p 0.05
R = 0.05
TYP
PIN 1 NOTCH
R = 0.20 OR 0.35
s 45o CHAMFER
2.50 REF
R = 0.115
TYP
27
28
0.40 p 0.10
PIN 1
TOP MARK
(NOTE 6)
1
2
5.00 p 0.10
(2 SIDES)
3.50 REF
3.65 p 0.10
2.65 p 0.10
(UFD28) QFN 0506 REV B
0.200 REF
0.00 – 0.05
0.25 p 0.05
0.50 BSC
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WXXX-X).
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
3496ff
18
LT3496
Revision History
(Revision history begins at Rev F)
REV
DATE
DESCRIPTION
PAGE NUMBER
F
4/10
Added H-Grade and Revised Entire Data Sheet
1 through 20
3496ff
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
19
LT3496
Typical Application
Triple Buck-Boost Mode 100mA × 6 LED Driver
PVIN
10V TO 16V
C1
2.2µF
6 LEDs
100mA
L1
10µH
L2
10µH
LED1
1Ω
CAP1
D1
M2
TG2
3.9M
OVP2
100k
CAP2
D2
C3
1µF
C4
0.1µF
LED3
1Ω
CAP3
D3
C5
1µF
SW2
CAP1, CAP2, CAP3
LED1, LED2, LED3
VIN
PWM1, PWM2, PWM3
SHDN
LT3496
GND
3.9M
OVP3
100k
C6
0.1µF
PVIN
PVIN
PWM
SHDN
3.9M
1Ω
100k
SW1
3000:1 PWM Dimming at 120Hz
PWM
5V/DIV
M3
TG3
LED2
OVP1
C2
0.1µF
6 LEDs
100mA
L3
10µH
M1
TG1
VIN
3V TO 16V
C8
1µF
6 LEDs
100mA
C7
1µF
IL
0.5A/DIV
ILED
0.1A/DIV
PVIN
SW3
TG1, TG2, TG3
OVP1, OVP2, OVP3
VC1, VC2, VC3
VREF
fADJ
CTRL1, CTRL2, CTRL3
0.5µs/DIV
3496 TA06b
10k
470pF
3496 TA06
C1: MURATA GRM31MR71E225KA93
C2, C4, C6: MURATA GRM21BR71H104KA01B
C3, C5, C7: MURATA GRM31MR71H105KA88
C8: MURATA GRM31MR71E105KA93
D1-D3: DIODES DFLS160
L1-L3: TAIYO YUDEN NP04SZB 100M
M1-M3: ZETEX ZXMP6A13F
Related Parts
PART NUMBER
DESCRIPTION
COMMENTS
LT1618
Constant Current, 1.4MHz, 1.5A Boost Converter
VIN: 1.6V to 18V, VOUT(MAX) = 36V, IQ = 1.8mA, ISD < 1µA,
10-Pin MS Package
LT3453
1MHz, 800mA Synchronous Buck-Boost High Power
LED Driver
VIN: 2.7V to 5.5V, VOUT(MAX) = 5.5V, IQ = 2.5mA, ISD < 6µA,
QFN Package
LT3466
Dual Constant Current, 2MHz, High Efficiency White LED
Boost Regulator with Integrated Schottky Diode
VIN: 2.7V to 24V, VOUT(MAX) = 40V, IQ = 5mA, ISD < 16µA, DFN Package
LT3467/LT3467A
1.1A (ISW), 1.3MHz/2.1MHz, High Efficiency Step-Up
DC/DC Converters with Integrated Soft-Start
VIN: 2.4V to 16V, VOUT(MAX) = 40V, IQ = 1.2mA, ISD < 1µA,
ThinSOT™ Package
LT3474
Step-Down 1A 2MHz LED Driver
VIN: 4V to 36V, VOUT(MAX) = 15V, IQ = 2.6mA, ISD < 1µA,
TSSOP Package
LT3475
Dual Step-Down 1.5A, 2mV LED Driver
VIN: 4V to 36V, IQ = 6mA, ISD < 1µA, 20-Lead TSSOPE Package
LT3476
High Current 2MHz Quad 1.5A Output LED Driver
VIN: 2.8V to 16V, VOUT(MAX) = 33.5V, IQ = 5.5mA, ISD < 1µA,
38-Lead 5mm × 7mm QFN Package
LT3477
3A, 42V, 3MHz Step-Up Regulator with Dual Rail-to-Rail
Current Sense
VIN: 2.5V to 2.5V, VOUT(MAX) = 40V, IQ = 5mA, ISD < 1µA, QFN, 16-Pin
TSSOPE Packages
LT3478/LT3478-1
4.5A, 2.25MHz LED Driver with 3000:1 Ture Color PWM™ VIN: 2.8V to 36V, VOUT(MAX) = 40V, IQ = 6.1mA, ISD < 3µA, 16-Pin
TSSOPE Package
Dimming
LT3479
3A, Full-Featured DC/DC Converter with Soft-Start and
Inrush Current Protection
VIN: 2.5V to 24V, VOUT(MAX) = 40V, IQ = 6.5mA, ISD < 1µA,
DFN, TSSOP Packages
3496ff
20 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 l FAX: (408) 434-0507
l
www.linear.com
LT 0510 REV F • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 2007
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