LT3755/LT3755-1/LT3755-2
40V
IN
, 75V
OUT
LED Controllers
FeaTures
3000:1 True Color PWM™ Dimming
n
Wide Input Voltage Range: 4.5V to 40V
n
Output Voltage Up to 75V
n
Constant-Current and Constant-Voltage Regulation
n
100mV High Side Current Sense
n
Drives LEDs in Boost, Buck Mode, Buck-Boost Mode,
SEPIC or Flyback Topology
n
Adjustable Frequency: 100kHz to 1MHz
n
Open LED Protection
n
Programmable Undervoltage Lockout with Hysteresis
n
Improved Open LED Status Pin (LT3755-2)
n
Frequency Synchronization (LT3755-1)
n
PWM Disconnect Switch Driver
n
CTRL Pin Provides Analog Dimming
n
Low Shutdown Current: <1µA
n
Programmable Soft-Start
n
Thermally Enhanced 16-Lead QFN (3mm
×
3mm)
and MSOP Packages
n
DescripTion
The LT
®
3755, LT3755-1 and LT3755-2 are DC/DC control-
lers designed to operate as a constant-current source for
driving high current LEDs. They drive a low side external
N-channel power MOSFET from an internal regulated 7.15V
supply. The fixed frequency, current mode architecture
results in stable operation over a wide range of supply
and output voltages. A ground referenced voltage FB pin
serves as the input for several LED protection features,
and also makes it possible for the converter to operate
as a constant-voltage source. A frequency adjust pin
allows the user to program the frequency from 100kHz
to 1MHz to optimize efficiency, performance or external
component size.
The LT3755/LT3755-1/LT3755-2 sense output current at
the high side of the LED string. High side current sensing
is the most flexible scheme for driving LEDs, allowing
boost, buck mode or buck-boost mode configuration.
The PWM input provides LED dimming ratios of up to
3000:1, and the CTRL input provides additional analog
dimming capability.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. True Color PWM is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 7199560, 7321203.
applicaTions
n
n
n
High Power LED
Battery Chargers
Accurate Current Limited Voltage Regulators
Typical applicaTion
50W White Automotive LED Headlamp Driver
V
IN
8V TO
40V
22µH
4.7µF
1M
185k
V
IN
SHDN/UVLO
V
REF
332k
CTRL
INTV
CC
100k
40.2k
LT3755-2
ISN
GATE
OPENLED
PWM
SS
PWMOUT
RT
V
C
GND INTV
CC
10k
0.001µF
37551 TA01a
Efficiency vs V
IN
100
1M
4.7µF
FB
ISP
0.1
1A
23.7k
96
EFFICIENCY (%)
50W
LED
STRING
92
SENSE
88
0.015
84
80
0.01µF
28.7k
375kHz
4.7µF
0
10
20
V
IN
(V)
30
40
37551 TA01b
37551fd
LT3755/LT3755-1/LT3755-2
absoluTe MaxiMuM raTings
(Note 1)
V
IN
............................................................................40V
SHDN/UVLO
(Note 3) ................................................40V
ISP ISN .....................................................................75V
,
INTV
CC
...................................................... V
IN
+ 0.3V, 8V
GATE, PWMOUT (Note 4) ......................... INTV
CC
+ 0.3V
CTRL, PWM,
OPENLED
.............................................12V
V
C
, V
REF
, SS, FB ..........................................................3V
SYNC ..........................................................................8V
RT ............................................................................1.5V
SENSE......................................................................0.5V
Operating Junction Temperature Range (Notes 2, 5)
LT3755E/LT3755I ...............................–40°C to 125°C
LT3755H ...........................................–40°C TO 150°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
MSOP ............................................................... 300°C
pin conFiguraTion
TOP VIEW
CTRL
ISN
ISP
VC
16 15 14 13
V
REF
1
PWM 2
SYNC OR
OPENLED
3
SS 4
5
RT
6
SHDN/UVLO
7
INTV
CC
8
V
IN
17
GND
12 FB
11 PWMOUT
10 GATE
9 SENSE
PWMOUT
FB
ISN
ISP
VC
CTRL
V
REF
PWM
1
2
3
4
5
6
7
8
TOP VIEW
16
15
14
13
12
11
10
9
GATE
SENSE
V
IN
INTV
CC
SHDN/UVLO
RT
SS
SYNC OR
OPENLED
17
GND
UD PACKAGE
16-LEAD (3mm 3mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 68°C/W,
θ
JC
= 4.2°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
MSE PACKAGE
16-LEAD PLASTIC MSOP
T
JMAX
= 125°C (E, I GRADES), T
JMAX
= 150°C (H GRADE),
θ
JA
= 43°C/W,
θ
JC
= 4°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
LT3755EUD#PBF
LT3755IUD#PBF
LT3755EUD-1#PBF
LT3755IUD-1#PBF
LT3755EUD-2#PBF
LT3755IUD-2#PBF
TAPE AND REEL
LT3755EUD#TRPBF
LT3755IUD#TRPBF
LT3755EUD-1#TRPBF
LT3755IUD-1#TRPBF
LT3755EUD-2#TRPBF
LT3755IUD-2#TRPBF
PART MARKING*
LDGC
LDGC
LDMS
LDMS
LFJZ
LFJZ
PACKAGE DESCRIPTION
16-Lead (3mm
×
3mm) Plastic QFN
16-Lead (3mm
×
3mm) Plastic QFN
16-Lead (3mm
×
3mm) Plastic QFN
16-Lead (3mm
×
3mm) Plastic QFN
16-Lead (3mm
×
3mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
16-Lead (3mm
×
3mm) Plastic QFN
LT3755EMSE#PBF
LT3755EMSE#TRPBF
3755
16-Lead Plastic MSOP
–40°C to 125°C
LT3755IMSE#PBF
LT3755IMSE#TRPBF
3755
16-Lead Plastic MSOP
–40°C to 125°C
LT3755EMSE-1#PBF
LT3755EMSE-1#TRPBF
37551
16-Lead Plastic MSOP
–40°C to 125°C
LT3755IMSE-1#PBF
LT3755IMSE-1#TRPBF
37551
16-Lead Plastic MSOP
–40°C to 125°C
LT3755EMSE-2#PBF
LT3755EMSE-2#TRPBF
37552
16-Lead Plastic MSOP
–40°C to 125°C
LT3755IMSE-2#PBF
LT3755IMSE-2#TRPBF
37552
16-Lead Plastic MSOP
–40°C to 125°C
LT3755HMSE-2#PBF
LT3755HMSE-2#TRPBF
37552
16-Lead Plastic MSOP
–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/
37551fd
LT3755/LT3755-1/LT3755-2
elecTrical characTerisTics
PARAMETER
V
IN
Minimum Operating Voltage
V
IN
Shutdown I
Q
V
IN
Operating I
Q
(Not Switching)
V
REF
Voltage
V
REF
Line Regulation
SENSE Current Limit Threshold
SENSE Input Bias Current
SS Pull-Up Current
Error Amplifier
ISP/ISN Full-Scale Current Sense Threshold
ISP/ISN Full-Scale Current Sense Threshold at CTRL = 0V
CTRL Pin Range for Current Sense Threshold Adjustment
CTRL Input Bias Current
LED Current Sense Amplifier Input Common Mode Range (V
ISN
)
ISP/ISN Short-Circuit Threshold
ISP/ISN Short-Circuit Fault Sensing Common Mode Range (V
ISN
)
ISP/ISN Input Bias Current (Combined)
LED Current Sense Amplifier g
m
VC Output Impedance
VC Standby Input Bias Current
FB Regulation Voltage (V
FB
)
FB Amplifier g
m
FB Pin Input Bias Current
FB Open LED Threshold
FB Overvoltage Threshold
VC Current Mode Gain – (∆V
VC
/∆V
SENSE
)
Oscillator
Switching Frequency
Minimum Off-Time
R
T
= 100k
R
T
= 10k
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 24V,
SHDN/UVLO
= 24V, CTRL = 2V, PWM = 5V, unless otherwise noted.
CONDITIONS
V
IN
Tied to INTV
CC
SHDN/UVLO
= 0V, PWM = 0V
SHDN/UVLO
= 1.15V, PWM = 0V
PWM = 0V
100µA ≤ I
VREF
≤ 0µA
4.5V ≤ V
IN
≤ 40V
l
l
l
MIN
TYP
0.1
1.4
MAX
4.5
1
5
1.7
2.045
118
13
103
–7
1.1
100
75
200
3
UNITS
V
µA
µA
mA
V
%/V
mV
µA
µA
mV
mV
V
nA
V
mV
V
µA
µA
µS
kΩ
1.965
98
8
2.00
0.006
108
40
10
100
–9.5
50
Current Out of Pin
Current Out of Pin
FB = 0V, ISP = 48V
CTRL = 0V, FB = 0V, ISP = 48V
l
l
96
–12
0
2.9
115
Current Out of Pin
l
ISN = 0V
l
150
55
0
120
15000
0
PWM = 5V (Active), ISP = ISN = 48V
PWM = 0V (Standby), ISP = ISN = 48V
V
(ISP – ISN)
= 100mV
1V < VC < 2V
PWM = 0V
ISP = ISN
FB = V
FB
, ISP = ISN
Current Out of Pin
OPENLED
Falling (LT3755 and LT3755-2)
PWMOUT Falling
V
FB
–
65mV
V
FB
+
50mV
l
0.1
–20
1.232
1.220
1.250
1.250
480
40
V
FB
–
50mV
V
FB
+
60mV
4
90
925
100
1000
170
20
1.265
1.270
100
V
FB
–
40mV
V
FB
+
75mV
nA
V
V
µS
nA
V
V
V/V
125
1050
kHz
kHz
ns
37551fd
LT3755/LT3755-1/LT3755-2
elecTrical characTerisTics
PARAMETER
Linear Regulator
INTV
CC
Regulation Voltage
Dropout (V
IN
– INTV
CC
)
INTV
CC
Undervoltage Lockout
INTV
CC
Current Limit
INTV
CC
Current in Shutdown
Logic Inputs/Outputs
PWM Input High Voltage
PWM Input Low Voltage
PWM Pin Resistance to GND
PWMOUT Output Low (V
OL
)
PWMOUT Output High (V
OH
)
SHDN/UVLO
Threshold Voltage Falling
SHDN/UVLO
Rising Hysteresis
SHDN/UVLO
Input Low Voltage
SHDN/UVLO
Pin Bias Current Low
SHDN/UVLO
Pin Bias Current High
OPENLED
Output Low (V
OL
)
SYNC Pin Resistance to GND
SYNC Input High
SYNC Input Low
Gate Driver
t
r
GATE Driver Output Rise Time
t
f
GATE Driver Output Fall Time
GATE Output Low (V
OL
)
GATE Output High (V
OH
)
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 LT3755E, LT3755E-1 and LT3755E-2 are 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 LT3755I, LT3755I-1 and LT3755I-2 are
guaranteed to meet performance specifications over the –40°C to 125°C
operating junction temperature range. The LT3755H-2 is guaranteed to
meet performance specifications 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.
INTV
CC
–
0.05
Note 3:
For V
IN
below 6V, the
SHDN/UVLO
pin must not exceed V
IN
for
proper operation.
Note 4:
GATE and PWMOUT pins are driven either to GND or INTV
CC
by
internal switches. Do not connect these pins externally to a power supply.
Note 5:
The LT3755 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.
C
L
= 3300pF
C
L
= 3300pF
35
35
0.05
ns
ns
V
V
I
VIN
Drops Below 1µA
SHDN/UVLO
= 1.15V
SHDN/UVLO
= 1.30V
I
OPENLED
= 0.5mA (LT3755 and LT3755-2)
LT3755-1 Only
LT3755-1 Only
LT3755-1 Only
1.5
0.4
30
1.7
2.05
10
E-, I-Grades
H-Grade
l
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 24V,
SHDN/UVLO
= 24V, CTRL = 2V, PWM = 5V, unless otherwise noted.
CONDITIONS
MIN
7
I
INTVCC
= –10mA, V
IN
= 7V
3.9
29
SHDN/UVLO
= 0V, INTV
CC
= 7V
1.5
0.4
45
INTV
CC
–
0.05
1.185
1.175
1.220
20
0.4
2.5
100
200
1.245
1.245
60
0
50
TYP
7.15
350
4.1
34
8
4.3
40
12
MAX
7.3
UNITS
V
mV
V
mA
µA
V
V
kΩ
mV
V
V
V
mV
V
µA
nA
mV
kΩ
V
V
37551fd
LT3755/LT3755-1/LT3755-2
Typical perForMance characTerisTics
V
(ISP – ISN)
Threshold vs V
CTRL
120
100
V
(ISP – ISN)
THRESHOLD (mV)
V
(ISP – ISN)
THRESHOLD (mV)
80
60
40
20
0
–20
0
0.5
1
V
CTRL
(V)
37551 G01
T
A
= 25°C, unless otherwise noted.
V
(ISP – ISN)
Threshold
vs Temperature
103
102
101
100
99
98
97
–50 –25
V
CTRL
= 2V
V
(ISP – ISN)
Threshold vs V
ISP
103
102
101
100
99
98
97
V
CTRL
= 2V
V
(ISP – ISN)
THRESHOLD (mV)
0
20
40
60
ISP VOLTAGE (V)
80
37551 G02
1.5
2
0
25 50 75 100 125 150
TEMPERATURE (°C)
37551 G03
FB Regulation Voltage
vs Temperature
1.28
1.27
1.26
V
REF
(V)
1.25
V
FB
(V)
1.24
1.23
1.22
1.21
1.20
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
37551 G04
V
REF
Voltage vs Temperature
2.04
2.03
2.02
2.01
2.00
1.99
1.98
1.97
1.96
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
37551 G05
V
REF
Voltage vs V
IN
2.04
2.03
2.02
2.01
V
REF
(V)
2.00
1.99
1.98
1.97
1.96
0
10
20
V
IN
(V)
30
40
37551 G06
Switching Frequency vs R
T
10000
500
Switching Frequency
vs Temperature
R
T
= 26.7k
2.4
SHDN/UVLO
Hysteresis Current
vs Temperature
SWITCHING FREQUENCY (kHz)
SWITCHING FREQUENCY (kHz)
450
I
SHDN/UVLO
(µA)
25 50 75 100 125 150
TEMPERATURE (°C)
37551 G08
2.2
1000
400
2.0
100
350
1.8
10
10
R
T
(k)
100
37551 G07
300
–50 –25
0
1.6
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
37551 G09
37551fd
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