LT3475EFE#TRPBF [Linear]
LT3475/LT3475-1 - Dual Step-Down 1.5A LED Driver; Package: TSSOP; Pins: 20; Temperature Range: -40°C to 85°C;
| 型号： | LT3475EFE#TRPBF |
| 厂家： | 
Linear |
| 描述： | LT3475/LT3475-1 - Dual Step-Down 1.5A LED Driver; Package: TSSOP; Pins: 20; Temperature Range: -40°C to 85°C 驱动器 |
| 文件： | 总32页 (文件大小：419K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT3760
× 100mA
8-Channel
LED Driver
FeaTures
DescripTion
The LT®3760 is an 8-channel LED driver with a step-up
DC/DC controller capable of driving up to 45V of LEDs.
Each channel contains an accurate current sink with ±±2
currentmatching.Channelsfollowamasterprogrammable
current to allow between ±0mA to 100mA of LED current
per string. Channels can be paralleled for higher LED
n
Up to 45V of LEDs × 100mA, 8-Channel LED Driver
n
Wide Input Range : 6V to 40V (4.5V to 13V,
V Connected to INTV )
IN
CC
n
n
n
n
n
n
n
n
n
n
±2% LED Current Matching at 40mA (Typ 0.ꢀ%)
Up to 3000:1 True Color PWM™ Dimming Range
Single Resistor Sets LED Current (20mA to 100mA)
LED Current Regulated Even for PV > V
current. Output voltage adapts to variations in LED V for
F
IN
OUT
optimum efficiency and open LED faults do not affect the
Output Adapts to LED V for Optimum Efficiency
F
operation of connected LED strings.
Fault Flag + Protection for Open LED Strings
Protection for LED Pin to V
Short
OUT
The LT3760 allows a PWM dimming range up to 3000:1
and an analog dimming range up to ±5:1. Operating
frequency can be programmed from 100kHz up to 1MHz
usingasingleresistororsynchronizedtoanexternalclock.
Parallel Channels for Higher LED Current
Programmable LED Current Derating vs Temperature
Accurate Undervoltage Lockout Threshold with
Programmable Hysteresis
Programmable Frequency (100kHz to 1MHz)
Synchronizable to an External Clock
Additional features include: programmable maximum
n
n
V
OUT
for open LED protection, a fault flag for open LED,
programmable LED current derating vs temperature, mi-
cropower shutdown and internal soft-start. The LT3760 is
available in a thermally enhanced ±8-pin TSSOP package.
applicaTions
L, LT, LTC and 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, 73±1±03.
n
Automotive, Notebook and TV Monitor Backlighting
Typical applicaTion
Worst-Case Channels LED Current Matching
(Normalized to 8-Channel Average)
92% Efficient, 36W Backlight LED Driver
PV
IN
20V TO 36V
0.8
4.7µF
4.7µF
10µH
UP TO 45V OF LEDs PER STRING
V
IN
8V TO 14V
5×
0.4
0.0
V
IN
2.2µF
INTV
GATE
CC
4.7µF
499k
• • • •
SENSE
PGND
SHDN/UVLO
0.015Ω
40.2k
•
•
•
•
•
•
•
•
•
•
CTRL
PWM
V
–0.4
–0.8
OUT
LED1
LED2
LT3760
R
= 14.7k (I(LED) = 40mA)
ISET
•
•
REF
•
•
•
•
8 CHANNELS ×100mA
•
–50 –25
0
25
50 75
100 125
•
20k
LED7
JUNCTION TEMERATURE (°C)
3760 TA01
T
SET
LED8
3760 TA01
100k
30.9k 11k
20k
FAULT
V
IN
OVP
SET
GND RT
I
V
SYNC
SET
C
39.2k
1MHz
5.76k
10k
2.2nF
3760fc
1
LT3760
absoluTe MaxiMuM raTings
pin conFiguraTion
(Note 1)
TOP VIEW
V
, LED1-8 ............................................................60V
OUT
1
2
OVP
SET
28
27
26
25
24
23
22
21
20
19
18
17
16
15
CTRL
V , SHDN/UVLO, FAULT ...........................................40V
IN
PWM
T
V
I
SET
REF
INTV ......................................................................13V
CC
3
V
C
INTV above V .................................................. +0.3V
CC
IN
4
RT
SET
NC
PWM, CTRL, SYNC.....................................................6V
5
GND
LED8
LED7
LED6
LED5
PGND
V ...............................................................................3V
C
V
6
LED1
LED2
, RT, I , T , OVP .......................................±V
SET SET SET
7
REF
29
PGND
SENSE......................................................................0.4V
Operating Junction Temperature Range
8
LED3
9
LED4
10
11
12
13
14
PGND
SENSE
GATE
(Notes ±,3).............................................-40°C to 1±5°C
Storage Temperature Range ..................-65°C to 150°C
Lead Temperature (Soldering, 10 sec)...................300°C
V
OUT
SYNC
FAULT
INTV
CC
SHDN/UVLO
V
IN
FE PACKAGE
28-LEAD PLASTIC TSSOP
T
= 1±5°C, θ = ±8°C/W, θ = 10°C/W
JA JC
JMAX
EXPOSED PAD (PIN ±9) IS PGND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
LT3760EFE#PBF
LT3760IFE#PBF
TAPE AND REEL
PART MARKING*
LT3760FE
PACKAGE DESCRIPTION
TEMPERATURE RANGE
–40°C to 1±5°C
LT3760EFE#TRPBF
LT3760IFE#TRPBF
±8-Lead Plastic TSSOP
±8-Lead Plastic TSSOP
LT3760FE
–40°C to 1±5°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/
3760fc
2
LT3760
elecTrical characTerisTics The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT = 6V, RISET = 14.ꢀk unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
INPUT BIAS, REFERENCE
Minimum Operational V (To Allow GATE Switching)
V = 1.5V
IN
C
l
l
V
V
= INTV (Shorted)
4.±
5.5
4.5
6.0
V
V
IN
IN
CC
≠ INTV
CC
Operational V
V
IN
V
IN
= INTV (Shorted)
4.5
6
13
40
V
V
IN
CC
≠ INTV
CC
V
IN
Quiescent Current
CTRL = 0.1V, PWM = 0V
4.±
9.5
5.7
1±
mA
mA
CTRL = 0.1V, PWM = 1.5V, (Not Switching)
LED = 1.±V
1–8
V
V
Shutdown Current (V ≠ INTV ) (Not Shorted)
SHDN/UVLO = 0V, V =6V
0.1
±
µA
µA
IN
IN
CC
IN
SHDN/UVLO = 0V, V = 40V
10
IN
Shutdown Current (V = INTV (Shorted))
SHDN/UVLO = 0V, V = INTV = 4.5V
10
±0
±0
40
µA
µA
IN
IN
CC
IN
CC
CC
SHDN/UVLO = 0V, V = INTV = 13V
IN
l
l
SHDN/UVLO Threshold (Micropower) (Falling) (V
SHDN/UVLO Threshold (UVLO) (Falling)
)
SD
I
< ±0µA
VIN
0.3
0.7
V
V
1.414
1.476
1.538
3.±
(Stop Switching) (V
)
UV
l
l
SHDN/UVLO Pin Current
SHDN/UVLO = V - 50mV
SHDN/UVLO = V + 50mV
1.6
±.4
0
µA
µA
UV
UV
V
REF
V
REF
V
REF
Voltage
I
I
= 0µA
1.450
1.485
0.01
±
1.5±4
0.05
V
2/V
mV
VREF
VREF
Line Regulation
Load Regulation
= 0µA, 6V < V < 40V
IN
0 < I
< 150µA (Max)
VREF
OSCILLATOR
l
l
Frequency: f
Frequency: f
(100kHz)
(1MHz)
RT = 5±3k
RT = 39.±k
9±
101
1
11±
1.10
0.±
kHz
MHz
2/V
V
OSC
OSC
0.90
f
(1MHz) Line Regulation
RT = 39.±k, 6V < V < 40V
0.1
1.6
OSC
IN
RT Pin Voltage
RT = 39.±k
Minimum Off-Time
Minimum On-Time
(Note 5)
(Note 5)
170
190
±50
±50
nS
nS
SYNC Input High Threshold
SYNC Input Low Threshold
SYNC Input Current
±.±
V
V
0.6
SYNC = 0V
SYNC = 5V
0
±5
µA
µA
SYNC Frequency Range
RT = 5±3k
RT = 39.±k
0.1±
1.±
1.5
1.5
MHz
MHz
LINEAR REGULATOR (INTV
)
CC
INTV Regulation Voltage
V
= 1±V
IN
6.65
7
7.35
V
mV
V
CC
I
= 10mA
±50
3.8
3.4
57
Dropout (V - INTV
)
CC
INTVCC
IN
(Start Switching)
(Stop Switching)
INTV UVLO (+)
CC
V
INTV UVLO (-)
CC
l
INTV Current Limit
40
mA
CC
OVP/LED ERROR AMPLIFIERS
Transconductance (OVP)
Voltage Gain (OVP)
∆I = ±±.5µA
VC
4
5
µmhos
V/V
Transconductance (LED)
∆I = ±±.5µA
VC
33
µmhos
3760fc
3
LT3760
elecTrical characTerisTics The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT = 6V, RISET = 14.ꢀk unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
45
MAX
UNITS
V/V
µA
µA
µA
V
Voltage Gain (LED)
V Source Current (Out of Pin)
C
V = 1.5V, V
= 0.8V, OVP = 1.5V
10
C
LEDx
LEDx
LEDx
SET
V Sink Current (OVP)
C
V = 1.5V, V
= 0.8V, OVP = 0V
15
C
SET
V Sink Current (LED)
C
V = 1.5V, V
= 1.±V, OVP = 1.5V
9
C
SET
V Output High (clamp) (V
C
)
±.3
0.8
1.1
COH
V Output Low (clamp) (V
C
)
V
COL
V Switching Threshold (V
C
)
V
CSW
SENSE AMP
SENSE Input Current (Out of Pin)
SENSE Current Limit Threshold
Current Mode Gain
65
5±
6
µA
mV
V/V
mV
l
l
44
90
60
∆V(V )/∆V(SENSE)
C
SENSE Over Current Limit Threshold
LED CURRENT / CONTROL
100
110
I
Pin Voltage
CTRL = 1.5V
1.00
40.1
±0.7
100.7
1.1
V
mA
2
SET
LEDx Current (40mA) (R
= 14.7k)
V
V
V
= 1V, CTRL = 1.5V
= 1V, CTRL = 1.5V
= 1V, CTRL = 1.5V
38.3
95.5
41.9
±±
ISET
LEDx
LEDx
LEDx
l
LEDx Current Matching (40mA) (R
= 14.7k)
ISET
LEDx Current (100mA) (R
= 5.76k)
105.9
mA
V
ISET
LED Pin Regulation Voltage
Threshold
T
630
mV
SET
ANALOG DIMMING
CTRL Input Current (Out of Pin)
CTRL = 1V
CTRL = 0.04V
40
50
±00
±00
nA
nA
LEDx Current (Dimming ±5:1)
PWM DIMMING
V
= 1V, CTRL = 0.04V
1.6
mA
LEDx
PWM Input Low Threshold
PWM Input High Threshold
PWM Input Current
0.7
1
V
V
1.1
1.4
PWM = 1.5V
PWM = 6V
6
±4
µA
µA
V
OUT
Pin Current in PWM Mode V(V ) = 60V
PWM = 1.5V, V = 1V
LEDx
370
±0
µA
µA
OUT
PWM = 0V, V
= 1V
LEDx
LEDx Leakage Current
(PWM = 0V)
V
LEDx
V
LEDx
= 1V, V
= 1±V
= 60V
0.1
0.1
1
±
µA
µA
OUT
OUT
= 50V, V
FAULT DIAGNOSTICS
FAULT Output Sink Current
LED1 = Open, V
= 0.3V
0.3
0.6
mA
V
FAULT
LED Short Threshold (V
)
V
OUT
V
OUT
= 1±V
= 60V
6
6
x
SH
(V
– V
)
OUT
LEDx
LED Open Detection Threshold
V
= 1±V
0.5
V
OUT
3760fc
4
LT3760
elecTrical characTerisTics The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT = 6V, RISET =14.ꢀk unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
GATE DRIVER
GATE Driver Output Rise Time
GATE Driver Output Fall Time
GATE Output Low
V
V
= 1±V, C = 3300pF (Note 4)
30
30
nS
nS
V
IN
L
= 1±V, C = 3300pF (Note 4)
IN
L
I
= 0µA
0.1
GATE
GATE Output High
INTV = V = 7V
CC IN
GATE
I
= 0µA
6.95
V
OUTPUT VOLTAGE
V
Over Voltage Protection (OVP) Regulation Voltage
OVP = 0.±±V
1±.5
57
V
V
OUT
SET
OVP = 1V
SET
OVP Input Current (Out of Pin)
OVP = 0.±±V, V =1±V
OUT
40
±00
nA
SET
SET
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.
LT3760I is guaranteed to meet performance specifications from
- 40°C to 1±5°C junction temperature.
Note 3: For Maximum Operating Ambient Temperature, see
Thermal Calculations in the Applications Information section.
Note 2: The LT3760E is guaranteed to meet performance specifications
from 0°C to 1±5°C junction temperature. Specifications over the -40°C
to 1±5°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
Note 4: GATE rise and fall times are measured between 102 and 902
of INTV voltage.
CC
Note 5: See Duty Cycle Considerations in the Applications Information.
TA = 25°C, unless otherwise noted.
Typical perForMance characTerisTics
Worst-Case Channels LED
Current Matching
LED Current
vs Junction Temperature
LED Current
vs CTRL Pin Voltage
(Normalized to 8-Channel Average)
0.8
0.4
42
41
40
39
38
110
100
90
80
70
60
50
40
30
20
10
0
R
=
R
= 14.7k
ISET
ISET
5.76k
7.32k
9.76k
14.7k
29.4k
0.0
–0.4
R
ISET
= 14.7k (I(LED) = 40mA)
–0.8
–50 –25
0
25
50 75
100 125
–50 –25
0
25
50
75 100 125
0.00 0.25 0.50 0.75 1.00 1.25 1.50
JUNCTION TEMERATURE (°C)
JUNCTION TEMERATURE (°C)
CTRL (V)
3760 G01
3760 G02
3760 G03
3760fc
5
LT3760
Typical perForMance characTerisTics TA = 25°C, unless otherwise noted.
LED Current Waveforms
SHDN/UVLO Threshold
3000:1 PWM Dimming (100Hz)
VREF vs Junction Temperature
vs Junction Temperature
1.525
1.505
1.525
1.505
1.485
1.465
1.445
(FRONT COVER
APPLICATION)
I(LEDx)
40mA/DIV
1.485
1.465
I(L1)
1A/DIV
PWM
10V/DIV
3760 G04
5µs/DIV
1.445
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
JUNCTION TEMERATURE (°C)
JUNCTION TEMPERATURE (°C)
3760 G06
3760 G05
SHDN/UVLO Pin (Hysteresis)
Current vs Junction Temperature
VIN Shutdown Current
vs Junction Temperature
VIN Quiescent Current vs VIN
2.80
2.70
2.60
2.50
2.40
5
4
3
2
1
0
12
10
8
V
= 6V, SHDN/UVLO = 0V
R
= 14.7k
IN
ISET
PWM = 1.5V, NO SWITCHING,
V(LED ) = 1.2V, CTRL = 0.1V
1-8
6
4
PWM = 0V, CTRL = 0.1V
2
2.30
2.20
0
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
0
5
10 15 20 25 30 35 40
JUNCTION TEMPERATURE (°C)
JUNCTION TEMPERATURE (°C)
V
(V)
IN
3760 G07
3760 G08
3760 G09
VC High Clamp, Active
and Low Clamp Levels
vs Junction Temperature
VIN Quiescent Current
vs Junction Temperature
Switching Frequency
vs Junction Temperature
15
10
1100
1050
2.5
2.0
1.5
1.0
0.5
V
C
HIGH CLAMP
V
IN
= 6V, R
= 14.7k, CTRL = 0.1V
ISET
V
C
ACTIVE (SWITCHING)
PWM = 1.5V, NO SWITCHING,
1000
950
V(LED ) = 1.2V, CTRL = 0.1V
1-8
R
= 39.2k
T
5
0
V
C
LOW CLAMP
PWM = 0V, CTRL = 0.1V
900
0.0
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
JUNCTION TEMPERATURE (°C)
JUNCTION TEMPERATURE (°C)
JUNCTION TEMPERATURE (°C)
3760 G10
3760 G11
3760 G12
3760fc
6
LT3760
Typical perForMance characTerisTics TA = 25°C, unless otherwise noted.
INTVCC vs Current,
Junction Temperature
INTVCC vs Current,
Junction Temperature
INTVCC, UVLO(+), UVLO(–)
vs Junction Temperature
7.0
6.9
6.8
6.7
6.6
6.0
5.5
8
7
6
5
4
3
2
V
= 6V, PWM = 0V
V
= 12V
I
= 10mA, 20mA, 30mA
IN
IN
LOAD
INTV (REGULATED)
CC
INTV UVLO(+)
CC
I
= 40mA
5.00
LOAD
I
I
I
I
= 10mA
= 20mA
= 30mA
= 40mA
LOAD
LOAD
LOAD
LOAD
INTV UVLO(–)
CC
V
= 8V, PWM = 0V
IN
4.5
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
JUNCTION TEMPERATURE (°C)
JUNCTION TEMPERATURE (°C)
JUNCTION TEMPERATURE (°C)
3760 G13
3760 G14
3760 G15
INTVCC Current Limit
vs Junction Temperature
SENSE Threshold
vs Junction Temperature
Overvoltage Protection (OVP)
Level vs Junction Temperature
60
55
50
60.0
57.5
55.0
52.5
50.0
47.5
45.0
42.5
40.0
70
60
50
40
30
20
10
0
V
IN
= 6V, INTV = 0V
CC
OVP
= 1.0V
SET
INDUCTOR PEAK CURRENT THRESHOLD
(CYCLE-BY-CYCLE)
45
OVP
= 0.22V
50
SET
40
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
–50 –25
0
25
75 100 125
JUNCTION TEMPERATURE (°C)
JUNCTION TEMPERATURE (°C)
JUNCTION TEMPERATURE (°C)
3760 G16
3760 G17
3760 G18
VOUT - V(LEDx) Short Threshold
vs Junction Temperature
Minimum ON and OFF Times
vs Junction Temperature
GATE Rise/Fall Times
vs GATE Capacitance
7.00
6.75
250
225
200
175
150
125
100
120
100
80
60
40
20
0
V
= 8V
CC
IN
INTV = 7V
6.50
6.25
MINIMUM ON-TIME
MINIMUM OFF-TIME
V
V
= 60V
= 12V
OUT
FALL TIME
6.00
5.75
RISE TIME
OUT
5.50
5.25
5.00
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
0
5
10
15
20
JUNCTION TEMPERATURE (°C)
JUNCTION TEMPERATURE (°C)
C
(nF)
GATE
3760 G18
3760 G20
3760 G21
3760fc
7
LT3760
pin FuncTions
CTRL (Pin 1): CTRL pin voltage below 1V controls
V (Pin 14): Input Supply Pin. Must be locally bypassed
IN
LED current. CTRL voltage can be set by a resistor
with a 1µF capacitor to PGND.
divider from V , V
or an external voltage source.
IN
REF
SHDN/UVLO(Pin15): TheSHDN/UVLOpinhasanaccurate
1.476Vthresholdandcanbeusedtoprogramanundervolt-
agelockout(UVLO)thresholdforsysteminputsupplyusing
a resistor divider from supply to GND. A ±.4µA pin cur-
rent hysteresis allows programming of UVLO hysteresis.
SHDN/UVLO above 1.476V turns the part on and removes
a ±.4µA sink current from the pin. SHDN/UVLO < 0.7V
LED current derating versus temperature is achievable
if the voltage programmed at the CTRL pin has a negative
temperature coefficient using an external resistor divider
from V
pin to GND with temperature dependent
REF
resistance.
T
(Pin 2): Programs LT3760 junction temperature
SET
breakpoint past which LED current will begin to derate.
reduces V current < ±0µA. If the shutdown function is
IN
Program using a resistor divider from V to GND.
not required, it should be forced above 1.476V or con-
REF
nected directly to V .
IN
V
(Pin 3): 1.485V Reference Output Pin. This pin can
REF
supply up to 150µA. Can be used to program CTRL, T
FAULT (Pin 16): Active low if any or all LED strings have
an open fault. If fault(s) removed, FAULT flag returns high.
Fault status is only updated during PWM high state and
latched during PWM low.
SET
and OVP pin voltages using resistor dividers to GND.
SET
I
(Pin 4): Resistor to GND Programs LED pin current.
SET
See Table 6 in the Applications Information Section.
SYNC(Pin1ꢀ):Allowssynchronizationofboostconverter
switchingfrequencytoanexternalclock.RT resistorshould
NC (Pin 5): No Connect. Okay to leave open or to connect
to GND.
be programmed for f
±02 below SYNC frequency. If
OSC
LED (Pins 6 to 9, 20 to 23): 8 LED Driver Outputs. Each
unused, connect to GND.
x
outputcontainsanopencollectorconstantcurrentsink.LED
V
(Pin 18): Boosted Output Voltage of the Converter.
OUT
currents are programmable from ±0mA to 100mA using a
Connect a capacitor from this pin to PGND. Connect the
single resistor at the I pin. Connect the cathode of each
SET
anode of each LED (string) to V
.
OUT
LED string to an LED pin. Connect the anode of each LED
GND (Pin 24): Signal Ground.
string to V . Channels can be paralleled for greater LED
OUT
current or individually disabled (connect LED to V ).
OUT
RT (Pin 25): A resistor to GND programs switching fre-
quency f between 0.1MHz and 1MHz.
PGND(Pins10, 19, ExposedPadPin29):Powergrounds
for the IC and the converter. The package has an exposed
pad (Pin ±9) underneath the IC which is the best path for
heat out of the package. Pin ±9 should be soldered to
a continuous copper ground plane under the device to
reduce die temperature and increase the power capability
of the LT3760.
OSC
V (Pin 26): Output of Both Transconductance Error
C
Amplifiers for the Converter Regulation Loop. The most
commonly used gm error amplifier (LED) regulates V
OUT
to ensure no LED pin falls below 1V. The other gm error
amplifier (OVP) is activated if all LEDs fail open and a
regulated maximum V
is required. Connect a resistor
OUT
and capacitor in series from the V pin to GND.
SENSE (Pin 11): The Current Sense Input for the Control
Loop. Connect this pin to the sense resistor in the source
of the external power MOSFET.
C
PWM (Pin2ꢀ):InputPinforPWM DimmingControl.Above
1.4V allows converter switching and below 0.7V disables
switching. The PWM signal can be driven from 0V to 6V.
GATE (Pin 12): Drives the gate of an N-channel MOSFET
If unused, connect to V
from 0V to INTV .
REF.
CC
OVP (Pin28):ProgramsmaximumallowedV
regu-
INTV (Pin 13): A 7V LDO supply generated from V and
SET
OUT
CC
IN
lation level if all LEDs are open circuit. Program using a
used to power the GATE driver and some control circuitry.
resistor divider from V to GND.
Must be bypassed with a 4.7µF capacitor to PGND.
REF
3760fc
8
LT3760
block DiagraM
14
13
SHDN/UVLO
V
INTV
CC
7V(REGULATED)
UVLO(+) = 3.8V, UVLO(−) = 3.4V
IN
+
15
R
S
1.476V
–
GATE
12
Q
600k
V
C
SYNC
RT
EN
17
25
+
–
+
–
OSC
SLOPE
–
+
–
+
1.485V
52mV
100mV
OVER
CURRENT
REF
1.485V
+
–
PEAK
4.2V(+)
3.7V(−)
CURRENT
SENSE
11
18
EN
HICCUP__MODE
V
OUT
INTV
CC_UV
IN_UV
+
–
6V
V
LEDx
6 TO 9, 20 TO 23
SHDN_UV
PWM
EN
FAULT
SOFT
START
27
3
16
V
EN
REF
LED
LOGIC
SS
1V
+
+
+
–
CTRL
1
LED CURRENT
CONTROL
PWM
–
+
CHANNEL X
1.1V
56R
OVERVOLTAGE
AMP
–
+
LED AMP
+
–
R
V
PTAT
T
I
GND
PGND (10, 19, EXPOSED PAD (29))
V
C
OVP
SET
SET
SET
2
4
24
26
28
3760 BD
Figure 1. LT3ꢀ60 Block Diagram
operaTion
TheoperationoftheLT3760isbestunderstoodbyreferring
to the typical application circuit on the front page and the
Block Diagram in Figure 1. The LT3760 drives 8 strings
of LEDs by using a constant switching frequency, current
mode boost controller to generate a single output voltage
efficiency, V
regulates to the lowest possible voltage
OUT
allowabletomaintainregulatedcurrentineachLEDstring.
Any OPEN LED fault is indicated by the FAULT pin driven
low without effecting the operation of the connected LED
strings.
V
OUT
for the top (anode) of all LED strings. LED string
The Block Diagram in Figure 1 illustrates the key functions
of the LT3760. It can be seen that two external supplies,
current is generated and controlled by connection of the
bottom LED in each string (cathode) to a current source
contained in each corresponding LED pin. Each LED pin
contains an accurate current sink to ground, program-
mable between ±0mA to 100mA using a single resistor
V
and INTV , are generated by the LT3760. The V
REF
CC REF
pinprovidesaprecision1.485Voutputforusewithexternal
resistors to program the CTRL, OVP
pins. The INTV pin provides a regulated 7V output to
and T
input
SET
SET
CC
at the I pin. LED channels can be paralleled to achieve
SET
supply the gate driver for the boost controller GATE pin.
An accurate 1.476V threshold on the SHDN/UVLO pin
combinedwithaSHDN/UVLOpincurrenthysteresisallows
higher LED currents. For applications requiring less than
8 strings of LEDs, channels can be paralleled or disabled
(connect LED pin to V
before startup). For optimum
OUT
a programmable resistor divider from V to SHDN/UVLO
IN
3760fc
9
LT3760
operaTion
to define the turn on/off voltages for V . SHDN/UVLO pin
the LT3760 only allows MOSFET turn-on approximately
every ±ms. This hiccup mode significantly reduces the
power rating required for the MOSFET.
IN
current switches from ±.4µA to 0µA when SHDN/UVLO
pin voltage exceeds 1.476V.
TheLT3760constantswitchingfrequencyisprogrammable
from 100kHz up to 1MHz using a single resistor at the RT
pin to ground. A SYNC pin is also provided to allow an
externalclocktodefinetheconverterswitchingfrequency.
The GATE output provides a ±0.8A peak gate drive for an
external N-channel power MOSFET to generate a boosted
LED current programming and dimming can be achieved
using the I , CTRL and PWM pins. A single resistor at
SET
the I
pin programs LED current. Analog dimming of
SET
LED brightness is achieved using the CTRL pin below 1V.
PWM dimming of LED brightness is achieved by control-
ling the duty cycle of the PWM pin.
output voltage V
using a single inductor, Schottky
OUT
For robust operation the LT3760 monitors system
conditions and performs soft start for startup after any of
diode and output capacitor. With LED strings connected
from V to every LED pin, the lowest voltage on each
OUT
the following faults: V , SHDN or INTV voltages too low
IN
CC
LED pin is monitored and compared to an internal 1V
or MOSFET current too high. The LT3760, when entering
these faults, discharges an internal soft start node and
prevents switching at the GATE pin. When exiting these
faults the LT3760 ramps up an internal soft start node to
reference. V is regulated to ensure the lowest LED pin
OUT
voltage of any connected LED string is maintained at 1V.
If any of the LED strings are open, the LT3760 will ignore
the open LED pin. If all of the LED strings are open V
OUT
controlV pinvoltageriseandhencecontrolMOSFETpeak
C
charges up until a user programmable OVP (overvoltage
protection)levelisreached. ThisprogrammableOVPlevel
allows the user to protect against LED damage when the
LED strings are opened and then reconnected.
switchcurrentrise.Inadditionthesoftstartperiodgradually
ramps up switching frequency from approximately 332
to 1002 of full scale.
The LT3760 monitors each LED pin voltage. If the LED
Since the LT3760 boost controller uses a current mode
string has an open fault (V(LED )<0.5V) the FAULT flag
X
topology, the V pin voltage determines the peak current
C
is pulled low.
in the inductor of the converter and hence the duty cycle
of the GATE switching waveform. The basic loop uses a
pulse from an internal oscillator to set an RS flip-flop and
turn on the external power MOSFET. Current increases
For LED protection, the LT3760 CTRL pin allows an LED
current derating curve to be programmed versus the
ambient temperature of the LED strings. An NTC resistor
placed close to the LEDs decreases CTRL pin voltage and
hencedecreasesLEDcurrentasLEDambienttemperature
increases.
in the MOSFET and inductor until the V commanded
C
peak switch current is exceeded and the MOSFET is then
turned off. Inductor current is sensed during the GATE on
period by a sense resistor RS in the source of the external
N-channel power MOSFET. As with all current mode
converters, slope compensation is added to the control
path to ensure stability for duty cycles above 502. Any
over current fault condition in the MOSFET turns off the
MOSFETandtriggerssoftstartinternally.Inthisfaultmode
The LT3760 also allows it’s own junction temperature
to be monitored and regulated by derating LED currents
when a junction temperature programmed by the T
pin is exceeded.
SET
3760fc
10
LT3760
applicaTions inForMaTion
INTV Regulator Bypassing and Operation
Inductor
CC
The INTV pin is the output of an internal linear regula-
A list of inductor manufacturers is given in Table 1. How-
ever, there are many other manufacturers and inductors
that can be used. Consult each manufacturer for more
detailed information and their entire range of parts. Ferrite
cores should be used to obtain the best efficiency. Choose
an inductor that can handle the necessary peak current
without saturating. Also ensure that the inductor has a
CC
tor driven from V and is the supply for the LT3760 gate
IN
driver. The INTV pin should be bypassed with a 10V
CC
rated 4.7µF low ESR, X7R or X5R ceramic capacitor to
ensure stability and to provide enough charge for the gate
driver. For high enough V levels the INTV pin provides
IN
CC
a regulated 7V supply. Make sure INTV voltage does
CC
±
not exceed the V rating of the external MOSFET driven
low DCR (copper-wire resistance) to minimize I R power
GS
by the GATE pin. For low V levels the INTV level will
losses. Values between ±.±µH and 33µH will suffice for
most applications. The typical inductor value required for
agivenapplication(assuming502inductorripplecurrent
for example) can be calculated as:
IN
CC
depend on V and the voltage drop of the regulator. The
IN
INTV regulator has an undervoltage lockout which
CC
prevents gate driver switching until INTV reaches 3.8V
CC
and maintains switching until INTV falls below 3.4V.
CC
1
VOUT
1
fOSC
1-
•
• V
IN
This feature prevents excessive power dissipation in the
external MOSFET by ensuring a minimum gate drive level
V
IN
to keep R
low. The INTV regulator has a current
CC
DS(ON)
L =
VOUT
limit of 40mA to limit power dissipation inside the I.C.
Thiscurrentlimitshouldbeconsideredwhenchoosingthe
N-channel power MOSFET and the switching frequency.
0.5 •
•ILEDx • 8
V
IN
where:
The average current load on the INTV pin due to the
CC
LT3760 gate driver can be calculated as:
V
OUT
= (N • V ) + 1V
F
I
= Q • f
g OSC
INTVCC
(N = number of LEDs per string),
V = LED forward voltage drop,
where Q is the gate charge (at V = INTV ) specified
g
GS
CC
F
for the MOSFET and fosc is the switching frequency of the
I
= LED current per string
LEDx
LT3760 boost converter. It is possible to drive the INTV
CC
pin from a variety of external sources in order to remove
Example: For a 1±W LED driver application requiring 8
strings of 10 LEDs each driven with 40mA, and choos-
power dissipation from the LT3760 and/or to remove the
INTV current limitation of 40mA. An external supply for
ing V = 1±V, V
= (3.75V • 10) + 1V = 38.5V, I
=
CC
CC
IN
OUT
LEDx
INTV should never exceed the V pin voltage or the
40mA and f
= 1MHz the value for L is calculated as
IN
OSC
maximum INTV pin rating of 13V. If INTV is shorted
CC
IN
CC
1
3.±
1
106
(1-
) •
• 1±V
to the V pin, V operational range is 4.5V to 13V.
IN
L =
= 16.5µH
0.5 • 3.± • 40mA • 8
3760fc
11
LT3760
applicaTions inForMaTion
Table 1. Inductor Manufacturers
Schottky Rectifier
MANUFACTURER
Sumida
PHONE NUMBER
408-3±1-9660
605-886-4385
40±-563-6866
847-639-6400
561-998-4100
WEB
The external diode for the LT3760 boost converter must
be a Schottky diode, with low forward voltage drop
and fast switching speed. Table 3 lists several Schottky
manufacturers. The diodes average current rating must
exceed the application’s average output current. The
diode’s maximum reverse voltage must exceed the
maximum output voltage of the application. For PWM
dimming applications be aware of the reverse leakage of
the Schottky diode. Lower leakage current will drain the
output capacitor less during PWM low periods, allowing
for higher PWM dimming ratios. The companies below
offerSchottkydiodeswithhighvoltageandcurrentratings.
www.sumida.com
www.we-online.com
www.vishay.com
www.coilcraft.com
www.cooperet.com
Würth Elektronik
Vishay
Coilcraft
Coiltronics
Input Capacitor
TheinputcapacitoroftheLT3760boostconverterwillsup-
plythetransientinputcurrentofthepowerinductor.Values
between±.±µFand10µFwillworkwellfortheLT3760.Use
only X5R or X7R ceramic capacitors to minimize variation
over voltage and temperature. If inductor input voltage is
requiredtooperateneartheminimumallowedoperational
Table 3. Schottky Rectifier Manufacturers
MANUFACTURER
Diodes, Inc.
PHONE NUMBER
805-446-4800
888-743-78±6
631-360-±±±±
40±-563-6866
WEB
www.microsemi.com
www.onsemi.com
www.zetex.com
www.vishay.com
V for the I.C., a larger capacitor value may be required.
IN
On Semiconductor
Zetex
This is to prevent excessive input voltage ripple causing
dips below the minimum operating input voltage.
Vishay Siliconix
Output Capacitor
Power MOSFET Selection
LowESRceramiccapacitorsshouldbeusedattheLT3760
converter output to minimize output ripple voltage. Use
only X5R or X7R dielectrics as these materials retain their
capacitance over wider voltage and temperature ranges
thanotherdielectrics.Theoutputcapacitancerequirements
for several LED driver application circuits are shown in
Several MOSFET vendors are listed in Table 4. Consult the
factory applications department for other recommended
MOSFETs. The power MOSFET selected should have a
V
rating which exceeds the maximum Overvoltage
DS
Protection (OVP) level programmed for the application.
(See “Programming OVP level” in the Applications
Information section). The MOSFET should also have a
the Applications Information section for various I
,
LED
V , V , L and f
values. Some suggested capacitor
IN OUT
OSC
manufacturers are listed in Table ±.
low enough total gate charge Q (at 7V V ) and a low
g
OSC
GS
enough switching frequency (f ) to not exceed the
Table 2. Ceramic Capacitor Manufacturers
INTV regulator current limit, where loading on INTV
MANUFACTURER
TDK
PHONE NUMBER
516-535-±600
408-986-04±4
814-±37-1431
408-573-4150
843-448-9411
WEB
CC
CC
pin due to gate switching should obey,
www.tdk.com
www.kemet.com
www.murata.com
t-yuden.com
Kemet
I
= Q • f
≤ 40mA
GATE
g
OSC
Murata
Taiyo Yuden
AVX
www.avxcorp.com
3760fc
12
LT3760
applicaTions inForMaTion
In addition, the current drive required for GATE switching
where
should also be kept low in the case of high V voltages
IN
1
1−D
0.5
2
IL(PEAK)
=
• 8 •ILEDx • 1+
(see“ThermalConsiderations”intheApplicationsInforma-
tion section). The R
of the MOSFET will determine
DS(ON)
d.c. power losses but will usually be less significant
compared to switching losses. Be aware of the power
dissipation within the MOSFET by calculating d.c. and
switching losses and deciding if the thermal resistance
of the MOSFET package causes the junction temperature
to exceed maximum ratings.
V
IN(MIN)
D = MOSFET duty cycle = 1−
,
VOUT(MAX)
VOUT(MAX) = N• V
+1V
(
)
F(MAX)
N = number of LEDs in each string,
VF(MAX) = maximum LED forward voltage drop,
IN(MIN) = minimum input voltage to the inductor,
Table 4. MOSFET Manufacturers
MANUFACTURER
PHONE NUMBER
WEB
V
Vishay Siliconix
40±-563-6866
www.vishay.com
www.irf.com
ILED = current in each LED pin,
International Rectifier 310-±5±-7105
Fairchild 97±-910-8000
www.fairchildsemi.com
andthe0.5termrepresentsaninductorpeak-to-peakripple
current of 502 of average inductor current.
Power MOSFET: Current Sense Resistor
The scale factor of • 0.7 ensures the boost converter
can meet the peak inductor requirements of the loop by
accounting for the combined errors of the 5±mV sense
The LT3760 current mode boost converter controls peak
currentintheinductorbycontrollingpeakMOSFETcurrent
ineachswitchingcycle.TheLT3760monitorscurrentinthe
external N-channel power MOSFET by sensing the voltage
acrossasenseresistor(RS)connectedbetweenthesource
of the FET and the power ground in the application. The
length of these tracks should be minimized and a Kelvin
sense should be taken from the top of RS to the sense
pin. A 5±mV sense pin threshold combined with the value
of RS sets the maximum cycle-by-cycle peak MOSFET
current. The low 5±mV threshold improves efficiency and
determines the value for RS given by:
threshold, I
, RS and circuit efficiency.
LEDx
Example: For a 1±W LED driver application requiring 8
strings of 10 LEDs each driven with 40mA, and choosing
V
= 8V, V
= (4V • 10)+1V = 41V and I
IN(MIN)
OUT(MAX) LEDx
= 40mA, the value for RS is chosen as:
5±mV • 0.7
IL(PEAK)
5±mV • 0.7
RS ≤
≤
41
8
• 8 • 0.04 • 1+ 0.±5
(
)
5±mV • 0.7
5±mV • 0.7
RS ≤
≤
≤ 17.7 mΩ
±.05
IL(PEAK)
3760fc
13
LT3760
applicaTions inForMaTion
The power rating of RS should be selected to exceed
Soft Start
±
the I R losses in the resistor. The peak inductor current
To limit inductor inrush current and output voltage during
startuporrecoveryfromafaultcondition,theLT3760pro-
videsasoftstartfunction.TheLT3760whenenteringthese
faultswilldischargeaninternalsoftstartnodeandprevent
should be recalculated for the chosen RS value to ensure
the chosen inductor will not saturate.
Power MOSFET: Overcurrent and Hiccup Mode
switchingattheGATEpinforanyofthefollowingfaults:V ,
IN
For severe external faults which may cause the external
MOSFET to reach currents greater than the peak current
definedbyRSandthe5±mVsensepinthresholddescribed
above, the LT3760 has an overcurrent comparator which
triggers soft start and turns off the MOSFET driver for
currents exceeding,
SHDN/UVLOorINTV voltagestooloworMOSFETcurrent
CC
toohigh(seethetimingdiagraminFigure±).Whenexiting
these faults the LT3760 ramps up an internal soft start
node at approximately 0.5V/ms to control V pin voltage
C
rise and hence control MOSFET switch current rise. In ad-
dition the soft start period gradually ramps up switching
frequency from approximately 332 to 1002 of full scale.
100mV
I
=
(OVERCURRENT)
The conditions required to exit all faults and allow a soft
RS
start ramp of the V pin are listed in Figure ±. An added
C
In this fault mode the LT3760 only allows MOSFET turn
on for approximately 100ns every ±ms. This hiccup mode
significantly reduces the power rating required for the
MOSFET.
feature of the LT3760 is that it waits for the first PWM pin
active high (minimum ±00ns pulse width) before it allows
GATE
V
C
V
0.5V/ms
C MIN
CLAMP
0.4V + V (V SWITCHING
BE
BE
C
THRESHOLD)
0.1V + V
SS
(INTERNAL)
0.5V/ms
0.4V
0.1V
ANY OF THE FOLLOWING FAULTS
TRIGGERS SOFT START LATCH
WITH GATE TURNED OFF
IMMEDIATELY:
SOFT-START LATCH RESET REQUIRES
ALL CONDITIONS SATISFIED:
SOFT-START
LATCH SET:
SS (INTERNAL) < 0.2V, VIN ≥ 4.2V,
SHDN > 1.476V, INTV > 3.8V,
CC
V
< 3.7V, SHDN < 1.476V,
INTVCC < 3.4V
(EXTERNAL MOSFET) > 100mV/RS
IN
I
(EXTERNAL MOSFET) < 100mV/RS,
DSS
PWM > 1.4V (FOR AT LEAST 200ns)
I
DSS
3760 F02
Figure 2. LT3ꢀ60 Fault Detection and Soft Start Timing for VC Pin and Internal SS Node
3760fc
14
LT3760
applicaTions inForMaTion
the soft start of V pin to begin. This feature ensures that
UVLO pin. After part turn on, 0µA flows from the SHDN/
UVLO pin. Calculation of the turn on/off thresholds for a
system input supply using the LT3760 SHDN/UVLO pin
can be made as follows :
C
during startup of the LT3760 the soft start ramp has not
timed out before PWM is asserted high. Without this ‘wait
forPWM high’feature,systemswhichapplyPWM afterV
IN
and SHDN/UVLO are valid, can potentially turn on without
soft start and experience high inductor currents during
wake up of the converter’s output voltage. It is important
to note that when PWM subsequently goes low, the soft
start ramp is not held at its present voltage but continues
to ramp upwards. If the soft start ramp voltage was held
every time PWM goes low, this would cause very slow
startup of LED displays for applications using very high
PWM Dimming ratios.
R1
R±
VSUPPLY OFF = 1.476 1+
VSUPPLY ON = VSUPPLY OFF + ±.4µA •R1
(
)
An open drain transistor can be added to the resistor
divider network at the SHDN/UVLO pin to independently
control the turn off of the LT3760.
Programming Switching Frequency
Shutdown and Programming Undervoltage Lockout
The switching frequency of the LT3760 boost converter
can be programmed between 100kHz and 1MHz using a
The LT3760 has an accurate 1.476V shutdown threshold
at the SHDN/UVLO pin. This threshold can be used in
conjunction with a resistor divider from the system input
supply to define an accurate undervoltage lockout (UVLO)
threshold for the system (Figure 3). An internal hysteresis
current at the SHDN/UVLO pin allows programming of
hysteresis voltage for this UVLO threshold. Just before
part turn on, an internal ±.4µA flows from the SHDN/
single resistor (R ) connected from the RT pin to ground
T
(Figure 4). Connect the R resistor as close as possible to
T
the RT pin to minimize noise pick up and stray capacitance
(see “Circuit Layout Considerations” in the Applications
Information section). Table 5 shows the typical R values
T
required for a range of frequencies.
1000
900
800
700
600
500
V
SUPPLY
R1
R2
SHDN/UVLO
15
–
+
600k
1.476V
400
300
200
OFF ON
100
0
100
200
300
400
500
600
RT (kΩ)
3760 F04
3760 F03
Figure 4. Switching Frequency vs RT
Figure 3. Programming Undervoltage
Lockout (UVLO) with Hysteresis
3760fc
15
LT3760
applicaTions inForMaTion
Table 6. LED Current vs. RISET (1% resistors)
Selecting the optimum frequency depends on several
factors. Higher frequency allows reduction of inductor
size but efficiency drops due to higher switching losses.
Lower frequency allows higher operational duty cycles to
drive a larger number of LEDs per string from a low input
supply but require larger magnetics. In each application
the switching frequency can be tailored to provide the
optimum solution.
R
(kΩ)
LED CURRENT PER CHANNEL (mA)
ISET
±0
40
±9.4
14.7
9.76
7.3±
5.76
60
80
100
An extra 50ns should be added to these tested timings to
account for errors in the rise/fall times of the GATE and
DRAIN of the external MOSFET and the d.c. resistance of
the external MOSFET and inductor.
Table 5. Switching Frequency vs. RT (1% resistors)
SWITCHING FREQUENCY (kHz)
RT (kΩ)
5±3
100
±00
300
400
500
600
700
800
900
1000
±49
158
Synchronizing to an External Clock
115
The SYNC pin allows the LT3760 oscillator to be synchro-
nized to an external clock. The SYNC pin can be driven
from a logic level output, requiring less than 0.6V for a
logic level low and greater than ±.±V for a logic level high.
SYNC pin high or low periods should exists for at least
100ns. If unused, the SYNC pin should be tied to ground.
To avoid loss of slope compensation during synchroniza-
90.9
73.±
60.4
51.1
44.±
39.±
tion, the free running oscillator frequency (f ) of the
OSC
Duty Cycle Considerations
LT3760 should be programmed to 802 of the external
clock frequency.
When designing the LT3760 LED driver for a given
application, the duty cycle requirements should be
considered and compared to the minimum/maximum
achievabledutycyclesfortheLT3760GATEpin.Ifrequired,
the LT3760 switching frequency can be programmed to a
lowervaluetomeetthedutycyclerequirements.Ingeneral,
the minimum/maximum GATE duty cycles required for a
particular application are given by:
Programming LED Current
ThecurrentsourcetogroundateachLEDpinisprogrammed
using a single resistor R
connected from the I pin
ISET
SET
to ground according to the following equation:
590
RISET
( )
A CTRL > 1.1V
I LED
(
≈
)
(
)
X
MIN Duty Cycle = GATE Minimum On-Time • Switching
See Table 6 for resistor values and corresponding pro-
grammed LED.
Frequency f
OSC
MAX Duty Cycle = 1 – (GATE Minimum Off-Time •
Switching Frequency f
)
OSC
The typical values for LT3760 GATE pin minimum on
and off times versus temperature are shown in the Typi-
cal Performance Characteristics. The range of GATE pin
minimum on time and off times are given in the electrical
specifications.
3760fc
16
LT3760
applicaTions inForMaTion
Analog Dimming
turn LED currents on/off as quickly as possible. For PWM
low, the LT3760 turns off the boost converter, turns off
TheLT3760allowsforLEDdimming(brightnessreduction)
byanalogdimmingorbyPWM dimming. Analogdimming
uses the CTRL pin voltage below 1V to reduce LED
brightness by reducing LED current. For CTRL pin voltage
below 1V, the current in each LED pin is given by:
all LED channel currents and disconnects the V pin and
C
internal V
resistor divider connected to the OVP error
amplifier. This allows the part to quickly return to the last
OUT
state of operation when the PWM pin is returned high.
Some general guidelines for LED current dimming using
the PWM pin (see Figure 5):
590
RISET
I LED ≈ CTRL •
0.04 < CTRL < 1V
(
)
(
)
X
(1) PWM Dimming Ratio (PDR) = 1/(PWM Duty Cycle) =
For CTRL pin voltages below 40mV (greater than ±5:1
dimming) the LED current will approach zero current. The
CTRL pin voltage can be derived from a resistor divider
1/T
• f
ON(PWM) PWM
(±) Lower PWM frequency (f
) allows higher PWM
PWM
dimming ratios (Typically choose 100Hz to maximize PDR
and to avoid visible flicker which can occur for display
systems with refresh rates at frequencies below 80Hz)
from V
pin to ground or generated from an external
REF
source. If analog dimming is not required, the pin can be
directly connected to the V pin. The only drawback of
REF
analog dimming is that reducing LED current to reduce
the brightness of the LED also changes the perceived
color of the LED.
(3)Higherf valueimprovesPDR(allowslowerT
)
OSC
ON(PWM)
but will reduce efficiency and increase internal heating. In
general, minimum operational T = 3 • (1/f
)
OSC
ON(PWM)
(4) Lower inductor value improves PDR
(5) Higher output capacitor value improves PDR
PWM Dimming
Manyapplicationsrequireanaccuratecontrolofthebright-
ness of the LED(s). In addition, being able to maintain a
constant color over the entire dimming range can be just
as critical. For constant color LED dimming the LT3760
providesaPWM pinandspecialinternalcircuitrytoachieve
uptoa3000:1widePWM dimmingrange. Thisisachieved
by operating the LED at it’s programmed current and then
controlling the on time of that LED current. The duty cycle
of the PWM pin controls the on time of each LED pin
current source (Figure 5). For maximum PWM dimming
ratios (low PWM duty cycles) it is important to be able to
(6) Choose the Schottky diode for the LT3760 boost con-
verter for minimum reverse leakage current.
Programming LED Current Derating (Breakpoint and
Slope) versus LED Ambient Temperature (CTRL Pin)
LED data sheets provide curves of maximum allowed
LED current versus ambient temperature to warn against
damaging of the LED (Figure 6). The LT3760 LED driver
improves the utilization and reliability of the LED(s) by al-
90
80
T
PWM
ON(PWM)
RESISTOR
70
(= 1/f
)
PWM
T
OPTION A
60
PWM
50
LT3760
40
PROGRAMMED LED
CURRENT DERATING
30
INDUCTOR
CURRENT
CURVE
20
10
0
MAX I
LED
CURRENT
LED
0
10 20 30 40 50 60 70 80
T -TEMPERATURE (°C)
3760 F05
A
3760 F06
Figure 5. PWM Dimming Waveforms
Figure 6. LED Current Derating vs LED Ambient Temperature
3760fc
17
LT3760
applicaTions inForMaTion
lowing the programming of an LED current derating curve
versustheambienttemperatureoftheLED(s).Withoutthe
ability to back off LED currents as temperature increases,
many LED drivers are limited to driving the LED(s) at 502
or less of their maximum rated currents. This limitation
requires more LEDs to obtain the intended brightness
for the application. The LT3760 allows the LED(s) to be
programmed for maximum allowable current while still
protectingtheLED(s)fromexcessivecurrentsathightem-
perature.ThetemperaturebreakpointandtheslopeofLED
current versus ambient temperature can be programmed
using a simple resistor network shown in Figure 7.
possibletotheLED(s). Sincethetemperaturedependency
of an NTC resistor can be non-linear over a wide range of
temperatures it is important to obtain a resistor’s exact
values over temperature from the manufacturer. Hand
calculations of CTRL voltage can then be performed at
each given temperature and the resulting CTRL voltage
plotted versus temperature.
Table ꢀ. NTC Resistor Manufacturers
MANUFACTURER
Murata Electronics North America
TDK Corporation
WEB
www.murata.com
www.tdk.com
www.digikey.com
Digi-key
This is achieved by programming a voltage at the CTRL
pinwithanegativetemperaturecoefficientusingaresistor
divider with temperature dependent resistance (Figures 7
and 8). A variety of resistor networks and NTC resistors
with different temperature coefficients can be used to
achieve the desired CTRL pin voltage behavior versus
temperature. The current derating curve in Figure 6 uses
the resistor network shown in option A of Figure 7.
IfcalculationofCTRLvoltageatvarioustemperaturesgives
a downward slope that is too strong, alternative resistor
networks can be chosen (B,C,D in Figure 7) which use
temperature independent resistance to reduce the effects
of the NTC resistor over temperature. Murata Electronics
provides a selection of NTC resistors with complete data
over a wide range of temperatures. In addition, a software
tool is available which allows the user to select from dif-
ferent resistor networks and NTC resistor values and then
simulate the exact output voltage curve (CTRL pin behav-
ior) over temperature. Referred to on the website as the
‘Murata Chip NTC Thermistor Output Voltage Simulator’,
Table7showsalistofNTCresistormanufacturers/distribu-
tors. There are several other manufacturers available and
the chosen supplier should be contacted for more detailed
information.To useanNTCresistortomonitortheambient
temperature of the LED(s) it should be placed as close as
1.50
1.25
1.00
3
V
REF
R1
LT3760
1
CTRL
RESISTOR
OPTION A
R2
OPTION A TO D
0.75
0.50
0.25
R
Y
R
Y
R
NTC
R
R
X
R
R
R
X
NTC
NTC
NTC
0
10 20 30 40 50 60 70 80
- AMBIENT TEMPERATURE (°C)
T
A
3760 F08
A
B
C
D
3760 F07
Figure 8. Programmed CTRL Voltage vs Temperature
Figure ꢀ. Programming LED Current Derating Curve
vs Ambient Temperature (RNTC Located on LED PCB)
3760fc
18
LT3760
applicaTions inForMaTion
userscanlogontowww.murata.com/designlibanddown-
WhilethisfeatureisintendedtodirectlyprotecttheLT3760,
it can also be used to derate the LED current at high tem-
peratures. Since there is a direct relationship between the
LED temperature and LT3760 junction temperature, the
TSET function also provides some LED current derating
at high temperatures.
load the software followed by instructions for creating an
output voltage ‘V ’ (LT3760 CTRL pin voltage) from a
OUT
specified V supply (LT3760 V
pin voltage). At any
CC
REF
time during selection of circuit parameters the user can
access data on the chosen NTC resistor by clicking on
the link to the Murata catalog. For a detailed example of
hand calculations using an NTC type resistor divider to
program CTRL pin voltage, read the LT3478 LED driver
data sheet section Programming LED Current Derating vs
Temperature under Applications Information.
Two external resistors program the maximum IC junction
temperature using a resistor divider from the V
pin,
REF
as shown in Figure 9. Choose the ratio of R1 and R± for
the desired junction temperature. Figure 10 shows the
relationship of T voltage to junction temperature, and
SET
Table 8 shows commonly used values for R1 and R±.
Using the T Pin for Thermal Protection
SET
The LT3760 contains a special programmable thermal
regulationloopthatlimitstheinternaljunctiontemperature
of the part. Since the LT3760 topology consists of a single
boostcontrollerwitheightlinearcurrentsources, anyLED
string voltage mismatch will cause additional power to be
dissipatedinthepackage.Thistopologyprovidesexcellent
current matching between LED strings and allows a single
power stage to drive a large number of LEDs, but at the
priceofadditionalpowerdissipationinsidethepart(which
means a higher junction temperature). Being able to limit
the maximum junction temperature allows the benefits of
this topology to be fully realized. This thermal regulation
featureprovidesimportantprotectionathighambienttem-
peratures, and allows a given application to be optimized
for typical, not worst-case, ambient temperatures with
the assurance that the LT3760 will automatically protect
itself and the LED strings under worst-case conditions.
3
V
REF
SET
R2
R1
LT3760
2
T
3760 F09
Figure 9. Programming the TSET Pin
950
900
850
800
750
700
650
600
550
500
V
PTAT
The operation of the thermal loop is simple. As the ambi-
ent temperature increases, so does the internal junction
temperature of the part. Once the programmed maximum
junction temperature is reached, the LT3760 begins to
linearly reduce the LED current, as needed, to try and
maintain this temperature. This can only be achieved
when the ambient temperature stays below the desired
maximum junction temperature. If the ambient tempera-
ture continues to rise past the programmed maximum
junction temperature, the LEDs current will be reduced
to approximately 52 of the full LED current.
0
25
50
150
75
100
125
JUNCTION TEMPERATURE (°C)
3760 F10
Figure 10. Programing the TSET Pin Threshold
Table 8. Resistor Values to Program Maximum IC Junction
Temperature (VREF (Typical) = 1.485V)
T (°C)
R1 (kΩ)
±4.9
R2 (kΩ)
±0
T
(V)
J
SET
100
115
130
0.8±4
0.866
0.90±
±8.0
±0
30.9
±0
3760fc
19
LT3760
applicaTions inForMaTion
Programming Overvoltage Protection (OVP) Level
startup when V
is low, the LT3760 ignores low LED
OUT
pin voltages until V
reaches 902 of its maximum al-
OUT
The LT3760 LED driver provides optimum protection to
the LEDs and the external MOSFET by providing a pro-
grammablemaximumregulatedoutputvoltagelimitusing
lowed OVP level. Once this condition is met, the LT3760
monitors all LED pins for open LED faults. To avoid false
detection of faults during PWM dimming edges (where
LED pins can possibly ring and trip fault detection levels)
theLT3760onlymonitors/updatesfaultconditionsduring
PWM high(andonlyafterablankdurationof±µsfollowing
each PWM rising edge).
the OVP
pin. The Overvoltage Protection (OVP) level
SET
is programmed as:
OVP(MAXIMUM REGULATED V ) = 57 • OVP
OUT
SET
If every LED string fails open or the multiple string LED
displaybecomesdisconnectedtheLT3760LEDdriverloop
regulates to the programmed OVP level. The OVP level
should be programmed to a level high enough to regulate
the LED strings but low enough to prevent damage to the
power switch and to minimize the voltage across the LED
pinsuponreconnectionoftheLEDstrings.Recommended
OVP level is given by:
LED Short Circuit
A short circuit fault between the positive terminal of an
LED string (V ) and the negative terminal of the LED
OUT
string (LEDx pin) causes the channel to be disabled in
order to protect the internal current source. A resistive
short is allowed as long as (V -V
) < 6V.
OUT LEDx
OVP(RECOMMENDED) = 1.2 • ((N • V ) + 1V)
F
Loop Compensation
where:
N = number of LEDs in each string,
Be sure to check the stability of the loop with the LEDs
connected (LED regulation loop) and disconnected
(Overvoltage Protection (OVP) regulation loop). Various
application circuits are shown in the data sheet which
V = maximum LED forward voltage drop
F
and the scaling factor of 1.± accounts for variation in the
coverarangeofV ,V ,f ,outputpowerandinductor
generation of OVP from OVP
logic requirements.
pin voltage and startup
IN OUT OSC
SET
current ripple values. For application requirements which
deviate from the circuits shown in the data sheet be sure
to check the stability of the final application over the full
Example:Foraconverteroperatingwith10LEDsperstring
at a maximum forward voltage of 4V per LED, the OVP
level should be programmed to:
V
range, LED current range (if analog dimming) and
IN
temperaturerange.BeawarethatiftheV pincomponents
C
OVP(RECOMMENDED) = 1.± • (10 • 4)+ 1V = 49.±V
represent a dominant pole for the converter loop and they
(
)
have been adjusted to achieve stability, the V pin might
C
49.±
57
For OVP = 49.±V, OVP
=
= 0.863V
move more slowly during load transient conditions such
SET
as an all-LEDs-open fault. A slower moving V pin will
C
add to V
overshoot during an all-LEDs-open fault.
The OVP pin voltage can be generated using a resistor
OUT
SET
An alternative compensation approach is to place the
dominant pole of the converter loop at the output. This
requires an increased output capacitor value but will allow
a much reduced Vc capacitor. The combination will allow
divider from the REF pin.
LED Open Circuit and PWM Dimming Ratios
The LT3760 monitors each LED pin voltage to determine if
the LED string has an open fault (LED pin voltage < 0.5V).
If an open LED fault occurs, the FAULT flag is pulled low.
To avoidfalsedetectionoffaultsduringtheinitialconverter
V to move more quickly and V
to move more slowly
C
OUT
resulting in less overshoot during an all-LEDs-open fault.
3760fc
20
LT3760
applicaTions inForMaTion
Thermal Considerations
The exposed pad on the bottom of the package must be
soldered to the ground plane. The ground plane should
be connected to an internal copper ground plane with vias
placed directly under the package to spread out the heat
generated by the LT3760.
TheinternalpowerdissipationoftheLT3760comesfrom3
main sources: V quiescent current (I total), V current
IN
Q
IN
for GATE switching (I
) and the LT3760 LED current
GATE
sources. Since the maximum operational V voltage is
IN
40V, care should be taken when selecting the switching
Circuit Layout Considerations
frequency and type of external power MOSFET since the
As with all switching regulators, careful attention must
be given to PCB layout and component placement to
achieveoptimalthermal,electricalandnoiseperformance.
The exposed pad of the LT3760 should be soldered to a
continuous copper ground plane underneath the device
to reduce die temperature and maximize the power capa-
bility of the IC. The signal ground (GND, pin ±4) is down
current required from V for GATE switching is given by,
IN
I
= f
• Qg
GATE
OSC
where Q is the gate charge (at V = INTV ) specified
g
GS
CC
for the MOSFET and f
is the programmed switching
OSC
frequency for the LT3760. A low Q MOSFET should al-
g
ways be used when operating the LT3760 from high V
IN
voltages. The internal junction temperature of the LT3760
bonded to the exposed pad near the RT and V pins.
C
can be estimated as:
I
, R and V components should be connected to an
T C
area of ground copper connected to pin ±4. The OVP
SET
SET
T =T +[V • (I
+(f •Q ))+(8•I(LED )•1.1V)]
OSC g X
J
• θ
A
IN QTOTAL
track should be kept away from fast moving signals and
not loaded with an external capacitor. GATE pin turn off
currents escape through a downbond to the exposed pad
and exit the PGND, pin 10. This area of copper and pin
10 should be the power ground (PGND) connection for
JA
where, T is the ambient temperature for the LT3760
A
I
representstheV quiescentcurrentfortheLT3760
QTOTAL
IN
(not switching, PWM = 1.5V and CTRL = 0.1V) - illustrated
in the Typical Characteristics Graphs – plus the base cur-
the inductor input capacitor, INTV capacitor and output
CC
rents of active channels (typically 8 • I(LED)/75). θ is
capacitor. A separate bypass capacitor for the V pin of
JA
IN
the thermal resistance of the package (±8°C/W for the
the IC may be required close the V pin and connected to
IN
±8-pin TSSOP package).
the copper area associated with signal ground, pin ±4. To
minimize MOSFET peak current sensing errors the sense
resistor(RS)shouldhaveKelvinconnectionstotheSENSE
pin and the power ground copper area near the pin. The
MOSFET drain rise and fall times are designed to be as
short as possible for maximum efficiency. To reduce the
effects of both radiated and conducted noise, the area of
the copper trace for the MOSFET drain should be kept as
small as possible. Use a ground plane under the switching
regulator to minimize interplane coupling. The Schottky
diode and output capacitor should be placed as close as
possible to the drain node to minimize this high switching
frequency path.
Example : For a 1±W LED driver application requiring 8
strings of 10 LEDs each driven with 40mA, V = ±4V, f
IN
OSC
= 1MHz, Q (at 7V V ) = 15nC, I(LED ) = 40mA, and an
g
GS
X
85°C ambient temperature for the LT3760 IC, the LT3760
junction temperature can be approximated as:
T = 85°C + [24 • (9.5mA + (8 • 40mA/75) + (1MHz
J
• 15nC)) + (8 • 40mA • 1.1V)] • 34
= 85°C + [(24 • 28.8mA) + (3±0mA • 1.1V)] • 34
= 85°C + (0.691W + 0.35W) • 34
= 85°C + 35°C
T = 1±0°C
J
3760fc
21
LT3760
Typical applicaTions
92% Efficient, 36W LED Driver, 1MHz Boost, 8 Strings, 100mA Per String
P
VIN
20V TO 36V
4.7µF
50V
L1
10µH
D1
UP TO 45V OF LEDs PER STRING
V
IN
8V TO 14V
4.7µF
25V
V
IN
2.2µF
100V
×5
INTV
CC
4.7µF
10V
M1
GATE
SENSE
PGND
V
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
IN
0.015Ω
LT3760
499k
100k
FAULT
V
OUT
SHDN/UVLO
40.2k
GND
LED1
LED2
LED3
LED4
LED5
LED6
LED7
LED8
SYNC
PWM
CTRL
PWM DIMMING
ANALOG DIMMING
3760 TA03
V
REF
20k
T
SET
LED Current Waveforms
3000:1 PWM Dimming (100Hz)
30.9k
11k
OVP
I
V
C
RT
SET
SET
(FRONT COVER
APPLICATION)
I(LEDx)
40mA/DIV
39.2k
5.76k 10k
2.2nF
20k
I(L1)
1A/DIV
L1: SUMIDA CDRH8D38
M1: VISHAY SILICONIX Si7850DP
D1: DIODES, INC. PDS360
PWM
10V/DIV
3760 G04
5µs/DIV
3760fc
22
LT3760
Typical applicaTions
28W LED Driver, ꢀ50kHz Boost, 8 Strings, 80mA Per String
L1
10µH
D1
UP TO 44V OF LEDs PER STRING
V
IN
11V TO 18V
4.7µF
25V
V
IN
2.2µF
100V
×7
INTV
CC
4.7µF
10V
M1
GATE
SENSE
PGND
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
0.0125Ω
LT3760
1M
100k
FAULT
V
OUT
SHDN
SHDN/UVLO
ANALOG
DIMMING
CTRL
GND
LED1
LED2
LED3
LED4
LED5
LED6
LED7
LED8
SYNC
PWM DIMMING
PWM
3760 TA04
V
REF
20k
T
SET
10k
OVP
I
V
C
RT
SET
SET
30.9k 16.9k
56.2k
7.32k 10k
4.7nF
L1: SUMIDA CDRH8D38
M1: VISHAY SILICONIX Si7308DN
D1: DIODES, INC. DFLS160
3760fc
23
LT3760
Typical applicaTions
15W LED Driver, ꢀ50kHz Boost, 8 Strings, 55mA Per String
L1
7.3µH
D1
UP TO 34V OF LEDs PER STRING
V
IN
8V TO 21V
4.7µF
50V
V
IN
2.2µF
50V
×5
INTV
CC
4.7µF
10V
M1
GATE
SENSE
PGND
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
0.015Ω
LT3760
100k
1M
FAULT
V
OUT
SHDN
SHDN/UVLO
ANALOG
DIMMING
CTRL
GND
LED1
LED2
LED3
LED4
LED5
LED6
LED7
LED8
SYNC
PWM DIMMING*
PWM
3760 TA05
V
REF
20k
T
SET
10k
OVP
I
V
C
RT
SET
SET
30.9k 10k
56.2k
10.7k 5.1k
4.7nF
L1: SUMIDA CDRH8D28
M1: VISHAY SILICONIX Si7308DN
D1: DIODES, INC. DFLS160
*MAXIMUM PWM DIMMING RATIO:
(a) f = 20kHz
PWM
= 20:1 (V > 10V)
IN
= 5:1 (V = 8V)
IN
(b) f
= 100Hz
PWM
= 3000:1 (V > 10V)
= 750:1 (V = 8V)
IN
IN
3760fc
24
LT3760
Typical applicaTions
29W LED Driver, 400kHz Boost, 2 Strings, 350mA Per String
L1
10µH
D1
UP TO 42V OF LEDs PER STRING
V
IN
8V TO 36V
4.7µF
50V
V
IN
2.2µF
INTV
CC
100V
M1
GATE
4.7µF
10V
×10
SENSE
PGND
•
•
•
•
•
•
0.007Ω
100k
LT3760
1M
FAULT
V
OUT
SHDN/UVLO
232k
GND
LED1
LED2
LED3
LED4
SYNC
PWM
CTRL
PWM DIMMING
LED5
LED6
LED7
LED8
3760 TA06
ANALOG DIMMING
V
REF
20k
T
SET
15k
OVP
I
V
C
RT
SET
SET
30.9k 23.2k
115k
6.65k
5.1k
4.7nF
L1: COOPER BUSSMANN HC9-100-R
M1: VISHAY SILICONIX Si7850DP
D1: DIODES, INC. PDS560
3760fc
25
LT3760
Typical applicaTions
25W LED Driver, 400kHz Boost, 3 Strings, 200mA Per String
L1
10µH
D1
UP TO 42V OF LEDs PER STRING
V
IN
8V TO 36V
4.7µF
50V
V
IN
2.2µF
INTV
100V
CC
M1
GATE
4.7µF
10V
×10
SENSE
PGND
•
•
•
•
•
•
•
•
•
0.007Ω
100k
LT3754
1M
FAULT
V
OUT
SHDN/UVLO
LED8
LED7
232k
GND
LED1
LED2
SYNC
PWM
CTRL
PWM DIMMING
LED3
LED4
ANALOG DIMMING
V
REF
LED5
LED6
3760 TA07
20k
T
SET
15k
OVP
I
V
C
RT
SET
SET
30.9k 23.2k
115k
5.76k
5.1k
4.7nF
L1: COOPER BUSSMANN HC9-100-R
M1: VISHAY SILICONIX Si7850DP
D1: DIODES, INC. PDS560
3760fc
26
LT3760
Typical applicaTions
29W LED Driver, ꢀ00kHz Boost, 4 Strings, 160mA Per String
L1
15µH
D1
UP TO 45V OF LEDs PER STRING
V
IN
10V TO 18V
4.7µF
25V
V
IN
2.2µF
100V
×5
INTV
CC
4.7µF
10V
M1
GATE
SENSE
PGND
V
•
•
•
•
•
•
•
•
•
•
•
•
IN
0.02Ω
LT3760
1M
100k
FAULT
V
OUT
SHDN/UVLO
SHDN
GND
LED1
LED2
SYNC
LED3
LED4
PWM
CTRL
PWM DIMMING
ANALOG DIMMING
LED5
LED6
V
REF
20k
LED7
LED8
T
SET
3760 TA08
11k
OVP
I
V
C
RT
SET
SET
30.9k
20k
60.4k
7.32k
7.5k
4.7nF
L1: SUMIDA CDRH8D38
M1: VISHAY SILICONIX Si7308DN
D1: DIODES, INC. DFLS160
3760fc
27
LT3760
Typical applicaTions
14W LED Driver, ꢀ00kHz Boost, 4 Strings, 80mA Per String (For Machine Vision Systems with Very Long Off-Times)
L1
15µH
1.5k
10k
D1
UP TO 45V OF LEDs PER STRING
5V/0V
ON/OFF
V
Q1
IN
10V TO 28V
4.7µF
50V
M2
1k
V
IN
2.2µF
INTV
100V
CC
4.7µF
10V
GATE
M1
×5
SENSE
PGND
V
•
•
•
•
•
•
•
•
•
•
•
•
IN
0.02Ω
LT3760
1M
100k
FAULT
V
OUT
SHDN/UVLO
SHDN
GND
LED1
LED2
SYNC
LED3
LED4
PWM
CTRL
PWM DIMMING
ANALOG DIMMING
LED5
LED6
V
REF
20k
M3
LED7
LED8
T
SET
3760 TA09
140k
20.5k
20k
OVP
I
V
C
RT
SET
SET
200pF
10k
30.9k
60.4k
7.32k
820pF
L1: SUMIDA CDRH8D38
M1: VISHAY SILICONIX Si7308DN
M2: VISHAY SILICONIX Si2309DS
M3: VISHAY SILICONIX Si2312DS
Q1: MMBTA42
D1: DIODES, INC. DFLS160
3760fc
28
LT3760
Typical applicaTions
13W LED Driver, 1MHz SEPIC, 8 Strings, 100mA Per String (Survives VOUT Short to PGND)
P
VIN
10V TO 32V
4.7µF
50V
2.2µF
50V
×2
L1A
15µH
D1
UP TO 16V OF LEDs PER STRING
V
OUT
V
IN
8V TO 14V
4.7µF
25V
•
L1B
15µH
V
IN
4.7µF
25V
×4
INTV
CC
4.7µF
10V
M1
GATE
SENSE
PGND
V
IN
0.015Ω
LT3760
499k
100k
100k
1M
FAULT
V
OUT
SHDN/UVLO
CTRL
GND
110k
LED1
LED2
LED3
LED4
LED5
LED6
LED7
LED8
SYNC
PWM
CTRL
PWM DIMMING
ANALOG DIMMING
3760 TA10
V
REF
20k
T
SET
30.9k
20k
OVP
I
V
C
RT
SET
SET
39.2k
5.76k 7.5k
4.7nF
6.34k
L1A, L1B: 15µH COUPLED INDUCTOR DRQ125
M1: VISHAY SILICONIX Si7850DP
D1: DIODES, INC. PDS560
3760fc
29
LT3760
package DescripTion
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
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 0.10
4.50 0.10
2.74
EXPOSED
PAD HEAT SINK
ON BOTTOM OF
PACKAGE
(.108)
SEE NOTE 4
6.40
(.252)
BSC
2.74
(.108)
0.45 0.05
1.05 0.10
0.65 BSC
RECOMMENDED SOLDER PAD LAYOUT
5
7
1
2
3
4
6
8
9 10 12 13 14
11
1.20
(.047)
MAX
4.30 – 4.50*
(.169 – .177)
0.25
REF
0° – 8°
0.65
(.0256)
BSC
0.09 – 0.20
(.0035 – .0079)
0.50 – 0.75
(.020 – .030)
0.05 – 0.15
(.002 – .006)
FE28 (EB) TSSOP 0204
0.195 – 0.30
(.0077 – .0118)
TYP
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS 4. RECOMMENDED MINIMUM PCB METAL SIZE
2. DIMENSIONS ARE IN
FOR EXPOSED PAD ATTACHMENT
MILLIMETERS
(INCHES)
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.150mm (.006") PER SIDE
3. DRAWING NOT TO SCALE
3760fc
30
LT3760
revision hisTory
REV
DATE
DESCRIPTION
PAGE NUMBER
A
1/11
Revised FAULT pin description.
8
1
B
10/11 Updated Features section.
Updated equation in “Power MOSFET: Current Sense Resistor” section.
13
18
Updated “Programming LED Current Derating (Breakpoint and Slope) versus LED Ambient
Temperature (CTRL Pin)” section.
C
3/1±
Corrected the inductor value formula.
11
3760fc
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
31
LT3760
relaTeD parTs
PART NUMBER
DESCRIPTION
COMMENTS
LT3755/LT3755- High Side 40V, 1MHz LED Controller with True Color
V
SD
= 4.5V to 40V, V
= 75V, 3,000:1 True Color PWM Dimming,
IN
OUT(MAX)
1/
3,000:1 PWM Dimming
I
= <1µA, 3mm × 3mm QFN-16 MSOP-16E
LT3755-±
LT3756/LT3756- High Side 100V, 1MHz LED Controller with True Color
V
SD
= 6V to 100V, V
= 100V, 3,000:1 True Color PWM Dimming,
OUT(MAX)
IN
1/
3,000:1 PWM Dimming
I
= <1µA, 3mm × 3mm QFN-16 MSOP-16E
LT3756-±
LT3598
LT3599
LT3595
LTC3783
LT3517
LT3518
44V, 1.5A, ±.5MHz Boost 6-Channel ±0mA LED Driver
44V, ±A, ±.5MHz Boost 4-Channel 100mA LED Driver
45V, ±.5MHz 16-Channel Full Featured LED Driver
V
= 3V to 30V (40V
), V
= 44V, 1,000:1 True Color PWM
IN
MAX
OUT(MAX)
Dimming, I = <1µA, 4mm × 4mm QFN-±4
SD
V
IN
= 3V to 30V (40V
), V
= 44V, 1,000:1 True Color PWM
MAX
OUT(MAX)
Dimming, I = <1µA, 4mm × 4mm QFN-±4
SD
V
SD
= 4.5V to 45V, V
= 45V, 5,000:1 True Color PWM Dimming,
IN
OUT(MAX)
I
= <1µA, 5mm × 9mm QFN-56
High Side 36V, 1MHz LED Controller with True Color
3,000:1 PWM Dimming
V
SD
= 3V to 36V, V
= 40V, 3,000:1 True Color PWM Dimming,
OUT(MAX)
IN
I
= <±0µA, 4mm × 5mm DFN-16 TSSOP-16E
1.5A, ±.5MHz High Current LED Driver with 3,000:1
Dimming
V
SD
= 3V to 30V, V
= 45V, 3,000:1 True Color PWM Dimming,
OUT(MAX)
IN
I
= <1µA, 4mm × 4mm QFN-16
±.3A, ±.5MHz High Current LED Driver with 3,000:1
Dimming
V
SD
= 3V to 30V, V
= 45V, 3,000:1 True Color PWM Dimming,
OUT(MAX)
IN
I
= <1µA, 4mm × 4mm QFN-16
LT3519/LT3519- 750mA, ±.±MHz High Current LED Driver
V
SD
= 3V to 30V, V
= 45V, 3,000:1 True Color PWM Dimming,
= 36V, 1,000:1 True Color PWM Dimming,
OUT(MAX)
IN
OUT(MAX)
1/
I
= <1µA, MSOP-16E
LT3519-±
LT3486
Dual 1.3A, ±MHz High Current LED Driver
V
SD
= 3V to 40V, V
= <1µA, 5mm × 3mm DFN, TSSOP-16E
IN
I
LT3478/LT3478-1 4.5A, ±MHz High Current LED Driver with 3,000:1
Dimming
V
SD
= ±.8V to 36V, V
= 60V, 3,000:1 True Color PWM Dimming,
OUT(MAX)
IN
I
= <10µA, 5mm × 7mm QFN-10
LT3496
Triple Output 750mA, ±.1 MHz High Current LED Driver
with 3,000:1 Dimming
V
SD
= 3V to 30V, V
= 40V, 3,000:1 True Color PWM Dimming,
IN
OUT(MAX)
I
= <1µA, 4mm × 5mm QFN-±8
LT3474/LT3474-1 36V, 1A (I ), ±MHz, Step-Down
V
SD
= 4V to 36V, V
= 13.5V, 400:1 True Color PWM Dimming,
= 4V to 36V, V = 13.5V, 3,000:1 True Color PWM Dimming,
OUT(MAX)
LED
IN
OUT(MAX)
LED Driver
I
= <1µA, TSSOP-16E
LT3475/LT3475-1 Dual 1.5A(I ), 36V, ±MHz, Step-Down LED Driver
V
SD
LED
IN
I
= <1µA, TSSOP-±0E
LT3476
LT3754
Quad Output 1.5A, ±MHz High Current LED Driver with
1,000:1 Dimming
V
SD
= ±.8V to 16V, V
= 36V, 1,000:1 True Color PWM Dimming,
IN
OUT(MAX)
I
= <10µA, 5mm × 7mm QFN-10
V
SD
= 6V to 40V, V
= 60V, 3,000:1 True Color PWM Dimming,
16-Channel × 50mA LED Driver
IN
OUT(MAX)
I
= <±µA, 5mm × 5mm QFN-3±
3760fc
LT 0312 REV C • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
32
●
●
LINEAR TECHNOLOGY CORPORATION 2009
(408) 43±-1900 FAX: (408) 434-0507 www.linear.com
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