LT3761
60V
IN
LED Controller with
Internal PWM Generator
FeaTures
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DescripTion
The LT
®
3761 is a DC/DC controller designed to operate as
a constant-current source and constant-voltage regulator.
It features a programmable internal PWM dimming signal.
The LT3761 is ideally suited for driving high current LEDs,
but also has features to make it suitable for charging bat-
teries and supercapacitors. The fixed frequency, current
mode architecture results in stable operation over a wide
range of supply and output voltages. A voltage feedback
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 LT3761 senses output current at the high side or at the
low side of the load. The PWM input can be configured to
self-oscillate at fixed frequency with duty ratio program-
mable from 4% to 96%. When driven by an external
signal, the PWM input provides LED dimming ratios of
up to 3000:1. The CTRL input provides additional analog
dimming capability.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
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.
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3000:1 True Color PWM™ Dimming for LEDs
Wide V
IN
Range: 4.5V to 60V
Rail-to-Rail Current Sense Range: 0V to 80V
Programmable PWM Dimming Signal Generator
Constant Current (±3%) and Constant-Voltage
(±2%) Regulation
Analog Dimming
Drives LEDs in Boost, SEPIC, Inverting, Buck Mode,
Buck-Boost Mode, or Flyback Configuration
Output Short-Circuit Protected Boost
Open LED Protection and Reporting
Adjustable Switching Frequency: 100kHz to 1MHz
Programmable V
IN
UVLO with Hysteresis
C/10 Indication for Battery Chargers
Low Shutdown Current: <1µA
Thermally Enhanced 16-Lead MSOP Package
applicaTions
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High Voltage LED Strings >100V with Ground
Referred Current Sense
Grounded Anode LEDs
Battery and SuperCap Chargers
Accurate Current Limited Voltage Regulators
Typical applicaTion
94% Efficient Boost LED Driver for Automotive
Headlamp with 25:1 Internal PWM Dimming
V
IN
8V TO
60V
10µH
2.2µF
×2
499k
90.9k
EN/UVLO
V
REF
1M
CTRL
INTV
CC
100k
DIM
140k
V
IN
GATE
SENSE
10m
GND
FB
2.2µF
×4
1M
0.25
1A
PWM Dimming Waveforms at
Various DIM Voltage Settings
V
DIM
= 7.7V
DC
PWM
= 96%
V
DIM
= 4V
DC
PWM
= 50%
60W
LED
STRING
I
LED
1A/DIV
V
DIM
= 1.5V
DC
PWM
= 10%
V
DIM
= 0.4V
DC
PWM
= 4.3%
0.5ms/DIV
3761 TA01b
LT3761
16.9k
124k
0.01µF
47nF
300Hz
ISP
OPENLED
ISN
DIM/SS
PWM
PWMOUT
V
C
RT INTV
CC
5.1k
4.7nF
28.7k
350kHz
INTV
CC
1µF
3761 TA01a
3761f
1
LT3761
absoluTe maximum raTings
(Note 1)
pin conFiguraTion
TOP VIEW
PWMOUT
FB
ISN
ISP
V
C
CTRL
V
REF
PWM
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
GATE
SENSE
V
IN
INTV
CC
EN/UVLO
RT
DIM/SS
OPENLED
V
IN
, EN/UVLO............................................................60V
ISP, ISN .....................................................................80V
INTV
CC
...................................................V
IN
+ 0.3V, 9.6V
GATE, PWMOUT ................................................ (Note 2)
CTRL,
OPENLED
........................................................15V
FB, PWM ..................................................................9.6V
V
C
, V
REF
......................................................................3V
RT, DIM/SS ..............................................................1.5V
SENSE ......................................................................0.5V
Operating Ambient Temperature Range (Notes 3, 4)
LT3761E ................................................. –40 to 125°C
LT3761I .................................................. –40 to 125°C
LT3761H ................................................ –40 to 150°C
Storage Temperature Range .................. –65°C to 150°C
17
GND
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
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3761EMSE#PBF
LT3761EMSE#TRPBF
3761
16-Lead Plastic MSOP
–40°C to 125°C
LT3761IMSE#PBF
LT3761IMSE#TRPBF
3761
16-Lead Plastic MSOP
–40°C to 125°C
LT3761HMSE#PBF
LT3761HMSE#TRPBF
3761
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/
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
V
REF
Pull-Up Current
SENSE Current Limit Threshold
SENSE Input Bias Current
DIM/SS Pull-Up Current
DIM/SS Voltage Clamp
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 24V, EN/UVLO = 24V, CTRL = 2V, PWM = 5V, unless otherwise noted.
CONDITIONS
V
IN
Tied to INTV
CC
EN/UVLO = 0V, PWM = 0V
EN/UVLO = 1.15V, PWM = 0V
PWM = 0V
–100µA ≤ I
VREF
≤ 0µA
4.5V ≤ V
IN
≤ 60V
V
REF
= 0V
Current Out of Pin, SENSE = 0V
Current Out of Pin, DIM/SS = 0V
I
DIM/SS
= 0µA
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l
MIN
TYP
0.1
1.8
MAX
4.5
1
6
2.2
2.05
210
118
14
UNITS
V
µA
µA
mA
V
%/V
µA
mV
µA
µA
V
1.955
150
98
10
2.02
0.001
185
105
40
12
1.2
3761f
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LT3761
elecTrical characTerisTics
PARAMETER
Error Amplifier
Full-Scale ISP/ISN Current Sense Threshold
(V
ISP-ISN
)
1/10th Scale ISP/ISN Current Sense Threshold
(V
ISP-ISN
)
Mid-Scale ISP/ISN Current Sense Threshold
(V
ISP-ISN
)
ISP/ISN Overcurrent Threshold
ISP/ISN Current Sense Amplifier Input Common Mode
Range (V
ISN
)
ISP/ISN Input Bias Current High Side Sensing (Combined)
ISP/ISN Input Bias Current Low Side Sensing (Combined)
ISP/ISN Current Sense Amplifier g
m
(High Side Sensing)
ISP/ISN Current Sense Amplifier g
m
(Low Side Sensing)
CTRL Pin Range for Linear Current Sense Threshold
Adjustment
CTRL Input Bias Current
V
C
Output Impedance
V
C
Standby Input Bias Current
FB Regulation Voltage (V
FB
)
FB Amplifier g
m
FB Pin Input Bias Current
FB Open LED Threshold
C/10 Inhibit for
OPENLED
Assertion (V
ISP-ISN
)
FB Overvoltage Threshold
V
C
Current Mode Gain (∆V
VC
/∆V
SENSE
)
Oscillator
Switching Frequency
GATE Minimum Off-Time
GATE Minimum On-Time
Linear Regulator
INTV
CC
Regulation Voltage
INTV
CC
Maximum Operating Voltage
INTV
CC
Minimum Operating Voltage
Dropout (V
IN
– INTV
CC
)
INTV
CC
Undervoltage Lockout
INTV
CC
Current Limit
INTV
CC
Current in Shutdown
INTV
CC
= 6V, 8V ≤ V
IN
≤ 60V
EN/UVLO = 0V, INTV
CC
= 8V
I
INTVCC
= –10mA, V
IN
= 7V
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The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 24V, EN/UVLO = 24V, CTRL = 2V, PWM = 5V, unless otherwise noted.
CONDITIONS
CTRL ≥ 1.2V, ISP = 48V
CTRL ≥ 1.2V, ISN = 0V
CTRL = 0.2V, ISP = 48V
CTRL = 0.2V, ISN = 0V
CTRL = 0.5V, ISP = 48V
CTRL = 0.5V, ISN = 0V
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MIN
242
243
21
20
96
95
0
TYP
250
257
25
28
100
105
600
MAX
258
268
30
36
104
115
80
UNITS
mV
mV
mV
mV
mV
mV
mV
V
µA
µA
µA
µS
µS
PWM = 5V (Active), ISP = ISN = 48V
PWM = 0V (Standby), ISP = ISN = 48V
PWM = 5V, ISP = ISN = 0V
V
ISP-ISN
= 250mV, ISP = 48V
V
ISP-ISN
= 250mV, ISN = 0V
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100
0.1
–230
120
70
0
50
15
–20
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1.0
100
20
1.255
500
40
100
V
FB
–
40mV
39
V
FB
+
70mV
1.275
V
nA
MΩ
nA
V
µS
nA
V
mV
V
V/V
Current Out of Pin
0.9V ≤ V
C
≤ 1.5V
PWM = 0V
ISP = ISN = 48V, 0V
FB = V
FB
, ISP = ISN = 48V
Current Out of Pin, FB = V
FB
OPENLED
Falling, ISP Tied to ISN
FB = V
FB
, ISN = 48V, 0V
PWMOUT Falling
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1.225
V
FB
–
65mV
14
V
FB
+
50mV
V
FB
–
50mV
25
V
FB
+
60mV
4
R
T
= 95.3kΩ
R
T
= 8.87kΩ
C
GATE
= 2200pF
C
GATE
= 2200pF
10V ≤ V
IN
≤ 60V
l
85
925
100
1000
160
180
115
1050
kHz
kHz
ns
ns
l
7.6
8.1
7.85
8.05
4.5
V
V
V
mV
V
mA
µA
3761f
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3.9
30
4.1
36
8
4.4
42
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LT3761
elecTrical characTerisTics
PARAMETER
Logic Inputs/Outputs
EN/UVLO Threshold Voltage Falling
EN/UVLO Rising Hysteresis
EN/UVLO Input Low Voltage
EN/UVLO Pin Bias Current Low
EN/UVLO Pin Bias Current High
OPENLED
Output Low
PWM Pin Signal Generator
PWM Falling Threshold
PWM Threshold Hysteresis (V
PWMHYS
)
PWM Pull-Up Current (I
PWMUP
)
PWM Pull-Down Current (I
PWMDN
)
PWM Fault Mode Pull-Down Current
PWMOUT Duty Ratio for PWM Signal Generator (Note 5)
I
DIM/SS
= 0µA
PWM = 0.7V, I
DIM/SS
= 0µA
PWM = 1.5V, I
DIM/SS
= 0µA
INTV
CC
= 3.8V
I
DIM/SS
= –6.5µA
I
DIM/SS
= 0µA
I
DIM/SS
= 21.5µA
I
DIM/SS
= 52µA
PWM = 47nF to GND, I
DIM/SS
= 0µA
C
L
= 560pF
C
L
= 560pF
PWM = 0V
INTV
CC
–
0.05
C
L
= 3300pF
C
L
= 3300pF
INTV
CC
–
0.05
25
25
0.1
3.1
6.8
40
95
215
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The
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denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 24V, EN/UVLO = 24V, CTRL = 2V, PWM = 5V, unless otherwise noted.
CONDITIONS
MIN
1.18
TYP
1.220
20
I
VIN
Drops Below 1µA
EN/UVLO = 1.15V
EN/UVLO = 1.33V
I
OPENLED
= 1mA
0.78
0.35
6
68
0.83
0.4
7.5
88
1.5
4.1
7.9
47.8
96.5
300
35
35
0.05
5.2
9.2
56
98
435
l
MAX
1.26
0.4
UNITS
V
mV
V
µA
nA
mV
V
V
µA
µA
mA
%
%
%
%
Hz
ns
ns
V
V
ns
ns
V
V
1.7
2.3
10
2.7
100
200
0.88
0.6
9
110
PWMOUT Signal Generator Frequency
PWMOUT, Gate Pin Drivers
PWMOUT Driver Output Rise Time (t
r
)
PWMOUT Driver Output Fall Time (t
f
)
PWMOUT Output Low (V
OL
)
PWMOUT Output High (V
OH
)
GATE Output Rise Time (t
r
)
GATE Output Fall Time (t
f
)
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:
Do not apply a positive or negative voltage or current source to
GATE or PWMOUT pins, otherwise permanent damage may occur.
Note 3:
The LT3761E is guaranteed to meet performance specifications
from the 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
LT3761I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The LT3761H is guaranteed over the full –40°C to
150°C operating junction temperature range. Operating lifetime is derated
at junction temperatures greater than 125°C.
Note 4:
The LT3761 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 junction temperature may impair device reliability.
Note 5:
PWMOUT Duty Ratio is calculated:
Duty = I
PWMUP
/(I
PWMUP
+ I
PWMDN
)
3761f
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LT3761
Typical perFormance characTerisTics
V
ISP-ISN
Threshold
vs CTRL Voltage
300
250
V
ISP -ISN
THRESHOLD (mV)
V
ISP-ISN
THRESHOLD (mV)
200
150
100
50
0
–50
0
0.5
1
1.5
CTRL VOLTAGE (V)
2
3761 G01
T
A
= 25°C, unless otherwise noted.
Full-Scale V
ISP-ISN
Threshold
vs Temperature
260
258
CTRL = 2V
V
ISP-ISN
Threshold
vs ISP Voltage
260
255
V
ISP -ISN
(mV)
256
254
252
250
248
246
ISN = 0
250
245
ISP = 48V
240
0
20
40
60
ISP VOLTAGE (V)
80
3761 G02
244
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3761 G03
FB Regulation Voltage (V
FB
)
vs Temperature
1.270
1.265
1.260
V
FB
(V)
1.255
1.250
1.245
1.240
–50 –25
300
250
200
150
100
50
V
ISP-ISN
Threshold vs FB Voltage
200
CTRL = 2V
V
REF
SOURCE CURRENT (µA)
190
180
170
160
V
REF
Source Current
vs Temperature
V
ISP-ISN
(mV)
CTRL = 0.5V
0
25 50 75 100 125 150
TEMPERATURE (°C)
3761 G04
0
1.20
1.21
1.22 1.23 1.24
FB VOLTAGE (V)
1.25
1.26
3761 G05
150
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3761 G06
V
REF
Voltage vs Temperature
2.06
2.05
SWITCHING FREQUENCY (kHz)
2.04
2.03
V
REF
(V)
2.02
2.01
2.00
1.99
1.98
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3761 G07
1000
900
800
Switching Frequency vs R
T
420
415
410
FREQUENCY (kHz)
405
400
395
390
385
10
R
T
(k )
100
3761 G08
Switching Frequency
vs Temperature
R
T
= 25.5k
700
600
500
400
300
200
100
380
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3761 G09
3761f
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