LINER LT3496 Triple output led driver Datasheet

LT3496
Triple Output LED Driver
FEATURES
DESCRIPTION
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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.
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True Color PWM™ Dimming Delivers Up to 3000:1
Dimming Ratio
Built-In Gate Driver for PMOS LED Disconnect
Three Independent Driver Channels with 750mA,
45V Internal Switches
Operates in Buck, Boost, Buck-Boost Modes
CTRL Pin Accurately Sets LED Current Sense
Threshold Over a Range of 10mV to 100mV
Adjustable Frequency: 330kHz to 2.1MHz
Open LED Protection
Wide Input Voltage Range:
Operation from 3V to 30V
Transient Protection to 40V
Surface Mount Components
28-Lead (4mm × 5mm) QFN and TSSOP Packages
APPLICATIONS
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RGB Lighting
Billboards and Large Displays
Automotive and Avionic Lighting
Constant-Current Sources
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.
The CTRL pin is used to adjust the LED current either for
analog dimming or overtemperature protection.
L, LT, LTC and LTM are registered 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
1μF
s3
3000:1 PWM Dimming at 120Hz
TG3
TG2
PWM
5V/DIV
7 LEDs
0.5A
0.5A
0.5A
0.47μF 0.47μF
18μH
IL
0.5A/DIV
0.47μF
18μH
ILED
0.5A/DIV
18μH
0.5μs/DIV
VIN
3V TO 24V
1μF
PWM1-3
SHDN
SW1
CAP1-3
LED1-3
VIN
PWM1-3
SHDN
SW2
LT3496
GND
SW3
TG1-3
VC1-3
VREF
CTRL1-3
FADJ
OVP1-3
3496 TA01b
22k
470pF
3496 TA01a
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LT3496
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN (Note 4) ...............................................................40V
SW1-SW3, LED1-LED3, CAP1-CAP3 ........................45V
TG1-TG3 ............................................ CAP – 10V to CAP
PWM1-PWM3 ...........................................................20V
VREF, CTRL1-CTRL3, FADJ, VC1-VC3, OVP1-OVP3 .2.5V
SHDN (Note 4) ...........................................................VIN
Operating Junction Temperature Range
(Note 2).................................................. –40°C to 125°C
Max Junction Temperature.................................... 125°C
Storage Temperature Range................... –65°C to 150°C
PIN CONFIGURATION
TOP VIEW
26 LED3
PWM1
4
25 CAP3
VREF
5
24 SW3
CTRL3
6
CTRL2
7
CTRL1
FADJ
LED3
3
TG3
PWM2
TOP VIEW
VIN
27 TG3
SHDN
28 VIN
2
PWM3
1
PWM2
SHDN
PWM3
28 27 26 25 24 23
PWM1 1
22 CAP3
VREF 2
21 SW3
23 SW2
CTRL3 3
20 SW2
22 CAP2
CTRL2 4
8
21 LED2
CTRL1 5
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
FE PACKAGE
28-LEAD PLASTIC TSSOP
TJMAX = 125°C, θJA = 25°C/W, θJC = 10°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
LED1
TG1
9 10 11 12 13 14
OVP1
15 OVP1
17 TG2
OVP2
16 TG1
OVP2 14
18 LED2
VC1
OVP3 13
19 CAP2
29
OVP3
29
UFD PACKAGE
28-LEAD (4mm s 5mm) PLASTIC QFN
TJMAX = 125°C, θJA = 43°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
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/
3496fe
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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, CAP1-3 = 5V, PWM1-3 = 5V, FADJ = 0.5V,
CTRL1-3 = 1.5V, OVP1-3 = 0V, unless otherwise noted.
PARAMETER
CONDITIONS
VIN Operation Voltage
(Note 4)
MIN
VIN Undervoltage Lockout
Full-Scale LED Current Sense Voltage
CAP1-3 = 24V
One-Tenth Scale LED Current Sense Voltage
CTRL1-3 = 100mV, CAP1-3 = 24V
VREF Line Regulation
3V ≤ VIN ≤ 40V, IREF = 10μA
Quiescent Current in Shutdown
SHDN = 0V
Quiescent Current Idle
UNITS
30
V
2.1
2.4
V
98
97
100
103
104
mV
mV
l
7.5
10
12.5
mV
2.5
IREF = 200μA, Current Out of Pin
MAX
l
CAPn/LEDn Operating Voltage
VREF Output Voltage
TYP
3
l
1.96
2
45
V
2.04
V
0.03
%/V
0.1
10
μA
PWM1-PWM3 = 0V
6
7.5
mA
Quiescent Current Active (Not Switching)
VC1-VC3 = 0V
11
14
mA
Switching Frequency
FADJ = 1.5V
FADJ = 0.5V
FADJ = 0.1V
1900
2100
1300
330
2300
kHz
kHz
kHz
Maximum Duty Cycle
FADJ = 1.5V (2.1MHz)
FADJ = 0.5V (1.3MHz)
FADJ = 0.1V (330kHz)
70
78
87
97
CTRL1-3 Input Bias Current
Current Out of Pin, CTRL1-3 = 0.1V
20
100
nA
FADJ Input Bias Current
Current Out of Pin, FADJ = 0.1V
20
100
nA
OVP1-3 Input Bias Current
Current Out of Pin, OVP1-3 = 0.1V
OVP1-3 Threshold
l
%
%
%
10
100
nA
0.95
1
1.05
V
–20
0
20
nA
VC1-3 Idle Input Bias Current
PWM1-3 = 0V
VC1-3 Output Impedance
CAP1-3 = 24V
4.5
MΩ
EAMP gm (ΔIVC/ΔVCAP-LED)
CAP1-3 = 24V
200
μS
SW1-3 Current Limit
(Note 3)
SW1-3 VCESAT
ISW = 500mA (Note 3)
SW1-3 Leakage Current
SHDN = 0V, SW = 5V
CAP1-3 Input Bias Current
750
1000
1250
260
180
mA
mV
2
μA
250
μA
CAP1-3, LED1-3 Idle Input Bias Current
PWM1-3 = 0V
1
μA
CAP1-3, LED1-3 Input Bias Current in Shutdown
SHDN = 0V
1
μA
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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, CAP1-3 = 5V, PWM1-3 = 5V, FADJ = 0.5V,
CTRL1-3 = 1.5V, OVP1-3 = 0V, unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
SHDN Input Low Voltage
UNITS
0.4
SHDN Input High Voltage
SHDN Pin Current
MAX
V
1.5
VSHDN = 5V, Current Into Pin
V
65
PWM1-3 Input Low Voltage
PWM1-3 Input High Voltage
100
μA
0.4
V
1.2
V
PWM1-3 Pin Current
Current Into Pin
160
210
μA
Gate Off Voltage (CAP1-3–TG1-3)
CAP1-3 = 40V, PWM1-3 = 0V
0.1
0.3
V
Gate On Voltage (CAP1-3–TG1-3)
CAP1-3 = 40V
6.5
7.5
V
Gate Turn-On Delay
CLOAD = 300pF, CAP1-3 = 40V (Note 5)
110
ns
Gate Turn-Off Delay
CLOAD = 300pF, CAP1-3 = 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.
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.
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LT3496
TYPICAL PERFORMANCE CHARACTERISTICS
Quiescent Current
(TA = 25°C unless otherwise noted)
Switch Current Limit
vs Duty Cycle
Switch On Voltage
14
1000
500
12
SWITCH CURRENT LIMIT (mA)
PWM1-3 = 5V
SWITCH VOLTAGE (mV)
INPUT CURRENT (mA)
400
10
8
PWM1-3 = 0V
6
4
300
200
100
800
600
400
200
2
VC = GND, NOT SWITCHING
0
0
10
20
0
40
30
0
0
200
VIN (V)
600
800
400
SWITCH CURRENT (mA)
3496 G01
1000
800
2250
2.03
2000
2.02
1750
VREF (V)
2.00
1000
1.99
1.97
50
25
75
0
TEMPERATURE (°C)
100
125
3496 G04
100
1250
1.98
0
–50 –25
80
1500
2.01
200
60
40
DUTY CYCLE (%)
Switch Frequency vs FADJ
2.04
SWITCH FREQUENCY (kHz)
1200
400
20
3496 G03
Reference Voltage
vs Temperature
600
0
3496 G02
Switch Current Limit vs
Temperature
CURRENT LIMIT (mA)
1000
1.96
–50 –25
750
500
250
75
50
25
TEMPERATURE (°C)
0
100
150
3496 G05
0
0
0.2
0.4
0.6
0.8
FADJ (V)
1.0
1.2
3496 G06
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LT3496
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Frequency vs Temperature
103
FADJ = 1.2V
2.2
2.1
2.0
VCAP-LED TRHESHOLD (mV)
VCAP-LED THRESHOLD (mV)
SWITCH FREQUENCY (MHz)
102
100
80
60
40
20
1.9
1.8
–50 –25
0
50
25
75
0
TEMPERATURE (°C)
100
125
101
100
99
98
97
0
0.2
0.4
0.6
0.8
CTRL (V)
1
0
1.2
10
20
30
VCAP (V)
40
VCAP-LED Threshold vs
Temperature
50
3496 G09
3496 G08
3496 G07
VCAP-LED THRESHOLD (mV)
CTRL = 1.2V
VCAP = 24V
2.3
102
VCAP-LED Threshold vs VCAP
VCAP-LED Threshold vs CTRL
120
2.4
103
(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
40V
TG
TG
30V
30V
98
97
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
VCAP = 40V
200ns/DIV
3496 G11
VCAP = 40V
200ns/DIV
3496 G12
3496 G10
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LT3496
PIN FUNCTIONS
PWM1, PWM2, PWM3: Pulse Width Modulated Input.
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.
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. CAPn-TGn 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 Input of Current Sense
Error Amplifier. 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 Input of Current Sense Error
Amplifier. 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 Pin for Disconnnect
P-Channel MOSFET. One for each converter. When the
Exposed Pad: Signal Ground and Power Ground. Solder
paddle directly to ground plane.
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LT3496
BLOCK DIAGRAM
D1
VSENSE
+
–
ILED
M1
C2
LED1
L1
VIN
C1
RSENSE 0.2Ω
CAP1
LED1
TG1
PWM1
SW1
A7
R3
OVP1
MOSFET
DRIVER
VC1
R4
–
RC
+
PWM1
CC
EAMP
+
V1
A1
–
1V
+
NPN
DRIVER
A6
–
A5
A4
Q1
R1 2k
1V
CTRL1
+
+
–
VC
SR LATCH
–
A3
A8
Q3
+
CTRL
BUFFER
R
A2
PWM
COMPARATOR
SLOPE
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
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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 VC (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
3496fe
9
LT3496
APPLICATIONS INFORMATION
dimming waveforms and the start-up time should be
checked across all operating conditions.
Open-LED Protection
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.
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.
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
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.
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.
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.
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.
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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
PART NUMBER
CMD4D06
Inductor Selection
CDRH4D28
CDRH5D28
SD3112
SD14
SD20
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:
Tayio 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.
IRMS (A)
SIZE
W × L × H (mm3)
2.2
0.116
0.95
3.5 × 4.3 × 0.8
3.3
0.174
0.77
2.2
0.072
1.20
3.3
0.085
1.10
4.7
0.105
0.90
10
0.128
1.00
15
0.149
0.76
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
10
0.2058
1.1
5.0 × 5.0 × 1.4
5.0 × 5.0 × 2.0
3.8 × 3.8 × 1.8
5.0 × 5.0 × 3.0
6.0 × 6.0 × 3.0
CooperET
Diode Selection
IF = IL • (1 – D)
DCR
(Ω MAX)
Sumida
CDRH3D16
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.
VALUE
(μH)
NR3015
NP04SZB
3.1 × 3.1 × 1.2
15
0.1655
1.25
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
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
3496fe
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
CTRL1-3
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.
3496fe
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
VIN
3V
C7
1μF
PWM1-3
SHDN
D1
SW1
CAP1-3
LED1-3
VIN
PWM1-3
SHDN
D2
C1-C3
1μF
s3
L2
15μH
L3
15μH
SW2
D3
SW3
OPEN
TG1-3
VC1-3
VREF
CTRL1-3
FADJ
OVP1-3
LT3496
GND
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 = 3V
CTRL = 0V TO 1.2V
PWM
5V/DIV
EFFICIENCY (%)
95
IL
0.5A/DIV
ILED
0.5A/DIV
5μs/DIV
90
85
3496 TA07b
80
75
0
50
100
150
200
ILED (mA)
250
300
3496 TA07c
3496fe
13
LT3496
TYPICAL APPLICATIONS
Triple Boost 100mA × 10 LED Driver
PVIN
12V
C1
2.2μF
L1
10μH
L2
10μH
D1
C2
1μF
L3
10μH
D2
CAP1
C3
1μF
1Ω
C4
1μF
1Ω
LED1
TG1
D3
CAP2
TG2
LED3
TG3
M2
825k
VIN
3V
C5
1μF
PWM1-3
SHDN
100mA
1Ω
LED2
M1
10 LEDs
CAP3
OVP1
20k
SW1
CAP1-3
LED1-3
VIN
PWM1-3
SHDN
M3
825k
10 LEDs
825k
OVP2
100mA
20k
SW2
10 LEDs
SW3
LT3496
GND
TG1-3
OVP1-3
VC1-3
VREF
FADJ
CTRL1-3
OVP3
100mA
20k
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
3496fe
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
C4
1μF
1Ω
LED1
CAP3
1Ω
LED2
LED3
M1
M2
825k
10 LEDs
100mA
825k
OVP1
10 LEDs
20k
SW1 TG1
VIN
3V TO 12V
C5
1μF
PWM
SHDN
SW2
CAP1-3
LED1-3
VIN
PWM1-3
SHDN
SW3 TG2
OVP1-3
TG3
VC1-3
VREF
FADJ
CTRL1-3
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
VIN
5V
C5
1μF
PWM1-3
SHDN
20mA
5Ω
LED2
8 LEDs
20k
C1: MURATA GRM31MR71C225KA35
C2-C5: MURATA GRM31MR71H105KA88
D1-D3: ZETEX ZLLS350
L1-L3: TAIYO YUDEN NP04SZB 220M
M1-M3: ZETEX ZXMP6A13F
TG3
M3
825k
OVP1
SW1
CAP1-3
LED1-3
VIN
PWM1-3
SHDN
LED3
M2
825k
8 LEDs
CAP3
C4
1μF
5Ω
LED1
TG1
D3
CAP2
SW2
LT3496
GND
20mA
825k
OVP2
8 LEDs
20k
OVP3
20mA
20k
SW3
TG1-3
OVP1-3
VC1-3
VREF
CTRL1-3
82k
FADJ
10k
470pF
20k
3496 TA08a
3496fe
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
M1
825k
OVP1-3
LED1
LED2
1Ω
CAP1
D1
C3
1μF
VIN
3V TO 16V
C8
1μF
PWM
SHDN
CAP3
D3
C4
0.1μF
PVIN
SW1
1Ω
CAP2
D2
C2
0.1μF
CAP1-3
LED1-3
VIN
PWM1-3
SHDN
LED3
1Ω
C5
1μF
C6
0.1μF
PVIN
SW2
LT3496
GND
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
20k
C7
1μF
PVIN
SW3 TG1
OVP1-3
TG2-3
VC1-3
VREF
FADJ
CTRL1-3
OPEN
10k
470pF
3496 TA05
3496fe
16
LT3496
TYPICAL APPLICATIONS
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
5.6k
C4
0.47μF
0.5A
5.6k
5.6k
M5
OVP1
2k
PWM1-3
SHDN
0.5A
C6
0.47μF
C5
0.47μF
M4
VIN
3V TO 24V
C7
1μF
20k
20k
0.5A
L1
10μH
SW1
CAP1-3
LED1-3
VIN
PWM1-3
SHDN
D1
D2
TG3
M3
20k
C1-C3
1μF
s3
L2
10μH
OVP2 OVP1
2k
SW2
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
M6
2k
L3
10μH
SW3
LT3496
GND
D3
TG1-3
OVP1-3
VC1-3
VREF
FADJ
CTRL1-3
22k
470pF
3496 TA02
3496fe
17
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 p 0.10
2.74
(.108)
4.50 p 0.10
SEE NOTE 4
0.45 p 0.05
EXPOSED
PAD HEAT SINK
ON BOTTOM OF
PACKAGE
6.40
2.74
(.252
(.108)
BSC
1.05 p 0.10
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
3496fe
18
LT3496
PACKAGE DESCRIPTION
UFD Package
28-Lead Plastic QFN (4mm × 5mm)
(Reference LTC DWG # 05-08-1712 Rev B)
0.70 p 0.05
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 p 0.05
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
PIN 1 NOTCH
R = 0.20 OR 0.35
s 45o CHAMFER
2.50 REF
R = 0.115
TYP
R = 0.05
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
0.25 p 0.05
0.200 REF
0.50 BSC
0.00 – 0.05
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
3496fe
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
LED1
1Ω
CAP1
D1
M2
TG2
3.9M
PWM
SHDN
M3
LED3
OVP2
1Ω
100k
CAP2
D2
C3
1μF
SW1
CAP1-3
LED1-3
VIN
PWM1-3
SHDN
3.9M
1Ω
C4
0.1μF
PVIN
3000:1 PWM Dimming at 120Hz
TG3
LED2
OVP1
100k
C2
0.1μF
6 LEDs
100mA
L3
10μH
M1
TG1
VIN
3V TO 16V
C8
1μF
6 LEDs
100mA
L2
10μH
CAP3
D3
C5
1μF
OVP3
100k
IL
0.5A/DIV
C6
0.1μF
PVIN
SW2
PWM
5V/DIV
3.9M
C7
1μF
ILED
0.1A/DIV
PVIN
SW3
LT3496
GND
TG1-3
OVP1-3
VC1-3
VREF
FADJ
CTRL1-3
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
ThinSOT and True Color PWM are trademarks of Linear Technology Corporation.
3496fe
20 Linear Technology Corporation
LT 1208 REV E • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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© LINEAR TECHNOLOGY CORPORATION 2007
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