LT3754IUH#TRPBF [Linear]
LT3754 - 16-Channel x 50mA LED Driver; Package: QFN; Pins: 32; Temperature Range: -40°C to 85°C;
| 型号： | LT3754IUH#TRPBF |
| 厂家： | 
Linear |
| 描述： | LT3754 - 16-Channel x 50mA LED Driver; Package: QFN; Pins: 32; Temperature Range: -40°C to 85°C 驱动 接口集成电路 |
| 文件： | 总30页 (文件大小：410K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT3754
× 50mA
16-Channel
LED Driver
FeaTures
DescripTion
The LT®3754 is a 16-channel LED driver with a step-up
DC/DC controller capable of driving up to 45V of LEDs.
Eachchannelcontainsanaccuratecurrentsinkwith±±.8%
currentmatching.Channelsfollowamasterprogrammable
current to allow between 10mA to 50mA of LED current
per string. Channels can be paralleled for higher LED
n
Up to 45V of LEDs × 50mA, 16-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
±2.8% LED Current Matching at 20mA (Typ 0.ꢀ%)
Up to 3000:1 True Color PWM™ Dimming Range
Single Resistor Sets LED Current (10mA to 50mA)
LED Current Regulated Even for PV > V
current. Output voltage adapts to variations in LED V for
IN
OUT
F
Output Adapts to LED V for Optimum Efficiency
optimum efficiency and open LED faults do not affect the
F
Fault Flag + Protection for Open LED Strings
Protection for LED Pin to V
operation of connected LED strings.
Short
OUT
The LT3754 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
n
n
Additional features include: programmable maximum
V
OUT
for open LED protection, a fault flag for open LED,
programmable LED current derating vs temperature,
micropowershutdownandinternalsoft-start.TheLT3754
is available in a thermally enhanced 5mm × 5mm 3±-pin
QFN package.
applicaTions
n
Automotive, Notebook and TV Monitor Backlighting
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.
Typical applicaTion
Worst-Case Channels LED Current Matching
(Normalized to 16-Channel Average)
92% Efficient, 36W Backlight LED Driver
PV
IN
24V
4.7µF
4.7µF
0.8
10µH
UP TO 45V OF LEDs PER STRING
V
IN
10V
5×
2.2µF
V
IN
0.4
0.0
INTV
GATE
CC
4.7µF
499k
• • • •
SENSE
SHDN/UVLO
0.015Ω
40.2k
•
•
•
•
•
•
•
•
•
•
•
•
CTRL
PWM
V
OUT
–0.4
–0.8
LT3754
LED1
LED2
•
•
R
= 14.7k (I(LED) = 20mA)
ISET
V
16 CHANNELS
REF
•
•
•
•
•
•
–50 –25
0
25
50 75
100 125
20k
LED15
LED16
JUNCTION TEMERATURE (°C)
T
SET
3754 TA01
3754 TA01
V
IN
100k
30.9k 11k
20k
FAULT
OVP
SET
GND RT
I
V
SYNC
SET
C
39.2k 5.76k
10k
2.2nF
3754fc
1
LT3754
absoluTe MaxiMuM raTings
pin conFiguraTion
(Note 1)
TOP VIEW
V
, LED1-16 ..........................................................60V
OUT
V , SHDN/UVLO, FAULT ...........................................40V
IN
INTV ......................................................................13V
CC
32 31 30 29 28 27 26 25
INTV above V ...................................................+0.3V
CC
IN
LED1
LED2
LED3
LED4
LED5
LED6
LED7
LED8
LED16
LED15
LED14
1
2
3
4
5
6
7
8
24
23
22
PWM, CTRL, SYNC.....................................................6V
V ...............................................................................3V
C
V
21 LED13
20 LED12
, RT, I , T , OVP .......................................±V
REF
SET SET SET
33
SENSE......................................................................0.4V
Operating Junction Temperature Range
(Notes ±,3).............................................–40°C to 1±5°C
Storage Temperature Range ..................–65°C to 150°C
19
18
17
LED11
LED10
LED9
9
10 11 12 13 14 15 16
UH PACKAGE
32-LEAD (5mm × 5mm) PLASTIC QFN
T
= 1±5°C, θ = 34°C/W, θ = 3°C/W
JA JC
JMAX
EXPOSED PAD (PIN 33) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
LT3754EUH#PBF
LT3754IUH#PBF
TAPE AND REEL
PART MARKING*
3754
PACKAGE DESCRIPTION
3±-Lead (5mm × 5mm) Plastic QFN
3±-Lead (5mm × 5mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 1±5°C
–40°C to 1±5°C
LT3754EUH#TRPBF
LT3754IUH#TRPBF
3754
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/
3754fc
2
LT3754
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
V
V
l
l
= INTV (Shorted)
4.±
5.5
4.5
6.0
V
V
IN
IN
CC
≠ INTV
CC
Operational V
V
= INTV (Shorted)
4.5
6
13
40
V
V
IN
IN
IN
CC
V
≠ INTV
CC
V
IN
Quiescent Current
LEDx = 1.±V
CTRL = 0.1V, PWM = 0V
CTRL = 0.1V, PWM = 1.5V, (Not Switching)
4.±
9.5
5.7
1±
mA
mA
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
%/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
%/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
6.65
7
7.35
V
mV
V
CC
IN
Dropout (V - INTV
)
CC
I = 10mA
INTVCC
±50
3.8
3.4
57
IN
INTV UVLO (+)
(Start Switching)
(Stop Switching)
CC
INTV UVLO (–)
V
CC
l
INTV Current Limit
44
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
3754fc
3
LT3754
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
SENSE = 0V
65
5±
6
µA
mV
V/V
mV
l
l
46
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
±0.±
±0.7
50.1
1.1
V
mA
%
SET
LEDx Current (±0mA) (R
= 14.7k)
V
V
V
= 1V, CTRL = 1.5V
= 1V, CTRL = 1.5V
= 1V, CTRL = 1.5V
19.±9
47.85
±1.11
±±.8
ISET
LEDx
LEDx
LEDx
l
LEDx Current Matching (±0mA) (R
= 14.7k)
ISET
LEDx Current (50mA) (R
= 5.76k)
5±.35
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
0.8
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
PWM = 0V
370
±0
µA
µA
OUT
LEDx Leakage Current
(PWM = 0V)
V
LEDx
V
LEDx
= 1V, V
= 1±V
OUT
0.1
0.1
1
±
µA
µA
OUT
= 50V, V
= 60V
FAULT DIAGNOSTICS
FAULT Output Sink Current
LED1 = Open, V
= 0.3V
0.3
0.6
mA
FAULT
LED Short Threshold (V
)
SH
V
OUT
V
OUT
= 1±V
= 60V
6
6
V
V
x
(V
– V
)
OUT
LEDx
LED Open Detection Threshold
V
= 1±V
0.5
V
OUT
3754fc
4
LT3754
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
= 7V, C = 3300pF (Note 4)
30
30
nS
nS
V
IN
L
= 7V, 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.
LT3754I 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 LT3754E 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 10% and 90%
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 16-channel Average)
0.8
0.4
21.00
20.50
20.00
19.50
19.00
55
50
45
40
35
30
25
20
15
10
5
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) = 20mA)
–0.8
0
–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)
3754 G01
3754 G02
3754 G03
3754fc
5
LT3754
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
I(LEDx)
20mA/DIV
1.485
1.465
I(L)
1A/DIV
PWM
10V/DIV
3754 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)
3754 G06
3754 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
1-16
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
3754 G07
3754 G08
3754 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,
V(LED ) = 1.2V, CTRL = 0.1V
1000
950
1-16
RT = 39.2k
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)
3754 G10
3754 G11
3754 G12
3754fc
6
LT3754
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)
3754 G13
3754 G14
3754 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)
3754 G16
3754 G17
3754 G18
V
OUT – V(LEDx) Short Threshold
Minimum ON and OFF Times
vs Junction Temperature
GATE Rise/Fall Times
vs GATE Capacitance
vs Junction Temperature
7.00
6.75
250
225
200
175
150
125
100
120
100
80
60
40
20
0
V
= 8V, INTV = 7V, RT = 523k
C
= 3300pF
IN
CC
GATE
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
3754 G18
3754 G20
3754 G21
3754fc
7
LT3754
pin FuncTions
LED (Pin1-8,1ꢀ-24):16LEDDriverOutputs.Eachoutput
RT (Pin 25): A resistor to ground programs switching
frequency f between 0.1MHz and 1MHz.
x
contains an open collector constant current sink. LED
OSC
currents are programmable from 10mA to 50mA using a
V (Pin 26): Output of Both Transconductance Error
C
single resistor at the I pin. Connect the cathode of each
SET
Amplifiers for the Converter Regulation Loop. The most
LED string to an LED pin. Connect the anode of each LED
commonly used gm error amplifier (LED) regulates V
OUT
string to V . Channels can be paralleled for greater LED
OUT
to ensure no LED pin falls below 1.1V. The other gm error
amplifier (OVP) is activated if all LEDs fail open and a
current or individually disabled (connect LED to V ).
OUT
SENSE (Pin 9): The Current Sense Input for the Control
Loop. Connect this pin to the sense resistor in the source
of the external power MOSFET.
regulated maximum V
is required. Connect a resistor
OUT
and capacitor in series from the V pin to ground.
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 10): Drives the gate of an N-channel MOSFET
from 0V to INTV .
CC
If unused, connect to V
REF.
INTV (Pin 11): A 7V LDO supply generated from V and
CC
IN
used to power the GATE driver and some control circuitry.
OVP
(Pin 28): Programs maximum allowed V
SET OUT
Must be bypassed with a 4.7µF capacitor to GND.
regulation level if all LEDs are open circuit.
V (Pin 12): Input Supply Pin. Must be locally bypassed
CTRL (Pin 29): CTRL pin voltage below 1V controls
IN
with a 1µF capacitor to ground.
maximum LED current. CTRL voltage can be set by a
resistordividerfromV ,V oranexternalvoltagesource.
IN REF
SHDN/UVLO(Pin13): TheSHDN/UVLOpinhasanaccurate
1.476Vthresholdandcanbeusedtoprogramanundervolt-
agelockout(UVLO)thresholdforsysteminputsupplyusing
a resistor divider from supply to ground. 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 with temperature dependent resistance.
REF
T
(Pin 30): Programs LT3754 junction temperature
SET
breakpoint past which LED current will begin to derate.
reduces V current < ±0µA. If the shutdown function is
IN
V
(Pin 31): 1.485V Reference Output Pin. This pin can
REF
not required, it should be forced above 1.476V or con-
supply up to 150µA. Can be used to program CTRL, T
SET
nected directly to V .
IN
andOVP pinvoltagesusingresistordividerstoground.
SET
FAULT (Pin 14): 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.
I
(Pin 32): Resistor to Ground Programs LED pin cur-
SET
rent. See Table 6 in the Applications Information Section.
Exposed Pad (Pin 33): GND. The ground for the IC and
the converter. The package has an exposed pad (Pin 33)
underneath the IC which is the best path for heat out of
the package. Pin 33 should be soldered to a continu-
ous copper ground plane under the device to reduce
die temperature and increase the power capability of
the LT3754.
SYNC(Pin15):Allowssynchronizationofboostconverter
switchingfrequencytoanexternalclock.RT resistorshould
be programmed for f
±0% below SYNC frequency. If
OSC
unused, connect to GND.
V
(Pin16): Boosted Output Voltage of the Converter.
OUT
Connect a capacitor from this pin to ground. Connect the
anode of each LED (string) to V
.
OUT
3754fc
8
LT3754
block DiagraM
12
11
SHDN/UVLO
V
IN
INTV
CC
7V(REGULATED)
UVLO(+) = 3.8V, UVLO(−) = 3.4V
13
+
R
S
1.476V
–
GATE
10
Q
600k
V
C
SYNC
15
EN
+
–
+
–
OSC
RT
SLOPE
25
–
+
–
+
1.485V
52mV
100mV
OVER
CURRENT
REF
1.485V
+
–
PEAK
4.2V(+)
3.7V(−)
CURRENT
SENSE
9
EN
HICCUP__MODE
V
OUT
INTV
CC_UV
IN_UV
SHDN_UV
16
+
–
6V
V
LEDx
1-8, 17-24
PWM
EN
FAULT
SOFT
START
27
31
14
V
EN
REF
LED
LOGIC
SS
1V
+
+
+
–
CTRL
29
LED CURRENT
CONTROL
PWM
–
+
CHANNEL X
1.1V
56R
R
OVERVOLTAGE
AMP
–
+
LED AMP
+
–
V
PTAT
T
I
V
C
OVP
SET
EXPOSED PAD (GND)
SET
SET
30
32
33
26
28
3754 BD
Figure 1. LT3ꢀ54 Block Diagram
operaTion
TheoperationoftheLT3754isbestunderstoodbyreferring
to the typical application circuit on the front page and the
Block Diagram in Figure 1. The LT3754 drives 16 strings
of LEDs by using a constant switching frequency, current
mode boost controller to generate a single output voltage
V
regulates to the lowest possible voltage allowable to
OUT
maintain regulated current in each LED string. Any OPEN
LED fault is indicated by the FAULT pin driven low without
effecting the operation of the connected LED strings.
The Block Diagram in Figure 1 illustrates the key functions
of the LT3754. It can be seen that two external supplies,
V
OUT
for the top (anode) of all LED strings. LED string
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
containsanaccuratecurrentsinktoground,programmable
V
and INTV , are generated by the LT3754. The V
REF
CC REF
pinprovidesaprecision1.485Voutputforusewithexternal
resistors to program the CTRL, OVP and T input
pins. The INTV pin provides a regulated 7V output to
supply the gate driver for the boost controller GATE pin.
An accurate 1.476V threshold on the SHDN/UVLO pin
combinedwithaSHDN/UVLOpincurrenthysteresisallows
SET
SET
CC
between 10mA to 50mA using a single resistor at the I
SET
pin. LED channels can be paralleled to achieve higher LED
currents. For applications requiring less than 16 strings
of LEDs, channels can be paralleled or disabled (connect
a programmable resistor divider from V to SHDN/UVLO
LED pin to V
before start-up). For optimum efficiency,
IN
OUT
3754fc
9
LT3754
operaTion
to define the turn on/off voltages for V . SHDN/UVLO pin
MOSFETandtriggerssoft-startinternally.Inthisfaultmode
the LT3754 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.
The LT3754 constant switching frequency is program-
mable from 100kHz up to 1MHz using a single resistor
at the RT pin to ground. A SYNC pin is also provided to
allow an external clock to define the converter switch-
ing frequency. The GATE output provides a ±0.8A peak
gate drive for an external N-channel power MOSFET to
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.
generate a boosted output voltage V
using a single
OUT
inductor, Schottky diode and output capacitor. With LED
strings connected from V to every LED pin, the lowest
For robust operation the LT3754 monitors system
conditionsandperformssoft-startforstart-upafteranyof
OUT
voltage on each LED pin is monitored and compared to
thefollowingfaults:V ,SHDNorINTV voltagestoolowor
IN
CC
an internal 1.1V reference. V is regulated to ensure
OUT
MOSFETcurrenttoohigh.TheLT3754,whenenteringthese
faults, discharges an internal soft-start node and prevents
switching at the GATE pin. When exiting these faults the
the lowest LED pin voltage of any connected LED string
is maintained at 1.1V. If any of the LED strings are open,
the LT3754 regulation loop will ignore the open LED pin.
LT3754 ramps up an internal soft-start node to control V
C
If all of the LED strings are open V
charges up until
OUT
pin voltage rise and hence control MOSFET peak switch
current rise. In addition the soft-start period gradually
ramps up switching frequency from approximately 33%
to 100% of full scale.
a user programmable OVP (overvoltage protection) level
is reached. This programmable OVP level allows the user
to protect against LED damage when the LED strings are
opened and then reconnected.
The LT3754 monitors each LED pin voltage. If the LED
Since the LT3754 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 LT3754 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 50%. Any
over current fault condition in the MOSFET turns off the
The LT3754 also allows its own junction temperature to
be monitored and regulated by derating LED currents
when a junction temperature programmed by the T
pin is exceeded.
SET
3754fc
10
LT3754
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 LT3754 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(assuming50%inductorripplecurrent
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
This feature prevents excessive power dissipation in the
1
VOUT
1
fOSC
1−
•
•VIN
external MOSFET by ensuring a minimum gate drive level
to keep R
low. The INTV regulator has a current
CC
DS(ON)
V
IN
L =
limit of 44mA to limit power dissipation inside the I.C.
Thiscurrentlimitshouldbeconsideredwhenchoosingthe
N-channel power MOSFET and the switching frequency.
V
0.5• OUT •ILEDx •16
V
where:
The average current load on the INTV pin due to the
CC
LT3754 gate driver can be calculated as:
V
OUT
= (N • V ) + 1V
F
I
= Q • f
g OSC
(N = number of LEDs per string),
INTVCC
where Q is the gate charge (at V = INTV ) specified
V = LED forward voltage drop,
g
GS
CC
F
for the MOSFET and f
is the switching frequency of the
OSC
I
= LED current per string
LEDx
LT3754 boost converter. It is possible to drive the INTV
CC
Example: For a 1±W LED driver application requiring 16
strings of 10 LEDs each driven with ±0mA, and choosing
pin from a variety of external sources in order to remove
power dissipation from the LT3754 and/or to remove the
V = 1±V, V
= (3.75V • 10) + 1V = 38.5V, I = ±0mA
INTV current limitation of 44mA. An external supply for
IN
and f
OUT
LEDx
CC
= 1MHz the value for L is calculated as
INTV should never exceed the V pin voltage or the
OSC
CC
IN
maximum INTV pin rating of 13V. If INTV is shorted
CC
CC
1
1
(1−
) •
• 12V
to the V pin, V operational range is 4.5V to 13V.
IN
IN
6
3.2
10
L =
= 16.5µH
0.5 • 3.2 • 20mA • 16
3754fc
11
LT3754
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 LT3754 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
TheinputcapacitoroftheLT3754boostconverterwillsup-
plythetransientinputcurrentofthepowerinductor.Values
between±.±µFand10µFwillworkwellfortheLT3754.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
V for the I.C., a larger capacitor value may be required.
www.microsemi.com
www.onsemi.com
www.zetex.com
www.vishay.com
IN
This is to prevent excessive input voltage ripple causing
On Semiconductor
Zetex
dips below the minimum operating input voltage.
Vishay Siliconix
Output Capacitor
LowESRceramiccapacitorsshouldbeusedattheLT3754
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
Power MOSFET Selection
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
≤ 44mA
GATE
g
OSC
Murata
Taiyo Yuden
AVX
www.avxcorp.com
3754fc
12
LT3754
applicaTions inForMaTion
In addition, the current drive required for GATE switching
52mV • 0.7
RS ≤
where
I
should also be kept low in the case of high V voltages
IN
I
L(PEAK)
(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.
1
0.5
=
• 16 •I
• 1+
L(PEAK)
LEDx
1− D
2
V
IN(MIN)
D = MOSFET duty cycle = 1–
V
OUT(MAX)
V
= N • V
+ 1V
(
)
OUT(MAX)
F(MAX)
Table 4. MOSFET Manufacturers
MANUFACTURER
PHONE NUMBER
WEB
N = number of LEDs in each string,
Vishay Siliconix
40±-563-6866
www.vishay.com
www.irf.com
V
V
= maximum LED forward voltage drop,
= minimum input voltage to the inductor,
F(MAX)
IN(MIN)
International Rectifier 310-±5±-7105
Fairchild 97±-910-8000
www.fairchildsemi.com
andthe0.5termrepresentsaninductorpeak-to-peakripple
current of 50% of average inductor current.
Power MOSFET: Current Sense Resistor
The LT3754 current mode boost converter controls peak
currentintheinductorbycontrollingpeakMOSFETcurrent
ineachswitchingcycle.TheLT3754monitorscurrentinthe
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:
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
threshold, I
, RS and circuit efficiency.
LEDx
Example: For a 1±W LED driver application requiring 16
strings of 10 LEDs each driven with ±0mA, and choosing
V
= 8V, V
= (4V • 10)+1V = 41V and I
IN(MIN)
OUT(MAX) LEDx
= ±0mA, the value for RS is chosen as:
52mV • 0.7
52mV • 0.7
RS ≤
≤
I
41
8
L(PEAK)
• 16 • 0.02 • 1+ 0.25
(
)
52mV • 0.7
≤
≤ 17.7 mΩ
2.05
3754fc
13
LT3754
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
start-uporrecoveryfromafaultcondition,theLT3754pro-
videsasoft-startfunction.TheLT3754whenenteringthese
faultswilldischargeaninternalsoft-startnodeandprevent
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 LT3754 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 LT3754 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 33% to 100% of full scale.
100mV
RS
ID(OVERCURRENT)
=
The conditions required to exit all faults and allow a soft-
start ramp of the V pin are listed in Figure ±. An added
C
In this fault mode the LT3754 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 LT3754 is that it waits for the first PWM pin
active high (minimum ±00ns pulse width) before it allows
the soft-start of V pin to begin. This feature ensures that
C
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
3754 F02
Figure 2. LT3ꢀ54 Fault Detection and Soft Start Timing for VC Pin and Internal SS Node
3754fc
14
LT3754
applicaTions inForMaTion
during start-up of the LT3754 the soft-start ramp has not
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 LT3754 SHDN/UVLO pin can be
made as follows :
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
start-up of LED displays for applications using very high
PWM Dimming ratios.
R1
R2
VSUPPLY OFF =1.476 1+
VSUPPLY ON = VSUPPLY OFF + 2.4µA •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 LT3754.
Programming Switching Frequency
Shutdown and Programming Undervoltage Lockout
The switching frequency of the LT3754 boost converter
can be programmed between 100kHz and 1MHz using a
The LT3754 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
partturnon, aninternal±.4µAflowsfromtheSHDN/UVLO
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
SHDN/UVLO
13
–
+
600k
R2
1.476V
400
300
200
OFF ON
100
0
100
200
300
400
500
600
RT (kΩ)
3754 F04
3754 F03
Figure 4. Switching Frequency vs RT
Figure 3. Programming Undervoltage
Lockout (UVLO) with Hysteresis
3754fc
15
LT3754
applicaTions inForMaTion
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.
Table 6. LED Current vs RISET (1% Resistors)
R
(kΩ)
LED CURRENT PER CHANNEL (mA)
ISET
10
±0
30
40
50
±9.4
14.7
9.76
7.3±
5.76
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 LT3754 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
LT3754 should be programmed to 80% of the external
clock frequency.
When designing the LT3754 LED driver for a given
application, the duty cycle requirements should be
considered and compared to the minimum/maximum
achievabledutycyclesfortheLT3754GATEpin.Ifrequired,
the LT3754 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:
295
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 LT3754 GATE pin minimum on- and
off-times versus temperature are shown in the Typical
Performance Characteristics. The range of GATE pin
minimum on-time and off-times are given in the electrical
specifications.
3754fc
16
LT3754
applicaTions inForMaTion
Analog Dimming
T
PWM
ON(PWM)
(= 1/f
)
PWM
T
TheLT3754allowsforLEDdimming(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:
PWM
INDUCTOR
CURRENT
295
RISET
I LED ≈CTRL •
0.04<CTRL <1V
MAX I
LED
(
)
(
)
LED
CURRENT
X
3754 F05
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
Figure 5. PWM Dimming Waveforms
from V
pin to ground or generated from an external
±. Lower PWM frequency (f
) allows higher PWM
REF
PWM
source. If analog dimming is not required, the pin can be
dimming ratios (typically choose 100Hz to maximize
PDR and to avoid visible flicker which can occur for
displaysystemswithrefreshratesatfrequenciesbelow
80Hz)
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
PWM Dimming
)
OSC
ON(PWM)
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 LT3754
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
turn LED currents on/off as quickly as possible. For PWM
low, the LT3754 turns off the boost converter, turns off
4. Lower inductor value improves PDR
5. Higher output capacitor value improves PDR
6. Choose the Schottky diode for the LT3754 boost conver-
ter for minimum reverse leakage current.
7. Start-Up
LT3754 V
start-up requires SHDN/UVLO and PWM
OUT
pins to be asserted from off to on and the PWM on-time
tobeaboveaminimumvalue. ThelowestPWM on-time
allowed for fault detection is ≈3.±µs. The lowest PWM
on-timeallowedforreachingV regulationistypically
OUT
3.±µsbutmightbegreaterdependingonexternalcircuit
parameters. Once LED current is in regulation, PWM
on-time can be further reduced depending on external
component selection.
all LED channel currents and disconnects the V pin and
C
internal V
resistor divider connected to the OVP error
OUT
amplifier. This allows the part to quickly return to the last
state of operation when the PWM pin is returned high.
8. V
Collapse
OUT
Some general guidelines for LED current dimming using
the PWM pin (see Figure 5):
If during normal operation V
collapses due to a
OUT
fault or because PWM on-time is too low, a restart is
required (see ‘Start-Up’ in item 7).
1. PWM Dimming Ratio (PDR) = 1/(PWM Duty Cycle) =
1/T
• f
ON(PWM) PWM
3754fc
17
LT3754
applicaTions inForMaTion
Programming LED Current Derating (Breakpoint and
Slope) versus LED Ambient Temperature (CTRL Pin)
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 C of Figure 7.
LED data sheets provide curves of maximum allowed
LED current versus ambient temperature to warn against
damaging of the LED (Figure 6). The LT3754 LED driver
improves the utilization and reliability of the LED(s) by al-
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 50%
or less of their maximum rated currents. This limitation
requires more LEDs to obtain the intended brightness
for the application. The LT3754 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.
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
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
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
www.murata.com
www.tdk.com
www.digikey.com
Digi-key
31
90
V
REF
8 LED STRINGS (2 × 40mA PER STRING)
80
R1
LT3754
29
RESISTOR
70
CTRL
OPTION A
60
50
R2
OPTION A TO D
LT3754
40
PROGRAMMED LED
CURRENT DERATING
CURVE
30
20
10
0
R
Y
R
Y
R
NTC
R
R
X
R
R
NTC
R
X
NTC
NTC
0
10 20 30 40 50 60 70 80
T -TEMPERATURE (°C)
A
A
B
C
D
3754 F06
3754 F07
Figure 6. LED Current Derating vs LED Ambient Temperature
Figure ꢀ. Programming LED Current Derating Curve
vs Ambient Temperature (RNTC Located on LED PCB)
3754fc
18
LT3754
applicaTions inForMaTion
1.50
Using the T Pin for Thermal Protection
SET
The LT3754 contains a special programmable thermal
regulationloopthatlimitstheinternaljunctiontemperature
of the part. Since the LT3754 topology consists of a single
boostcontrollerwithsixteenlinearcurrentsources,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 LT3754 will automatically protect
itself and the LED strings under worst-case conditions.
1.25
1.00
RESISTOR
OPTION A
0.75
0.50
0.25
0
10 20 30 40 50 60 70 80
- AMBIENT TEMPERATURE (°C)
T
A
3754 F08
Figure 8. Programmed CTRL Voltage vs Temperature
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
different resistor networks and NTC resistor values and
then simulate the exact output voltage curve (CTRL pin
behavior) over temperature. Referred to on the website as
the ‘Murata Chip NTC Thermistor Output Voltage Simula-
tor’, users can log onto www.murata.com/designlib and
downloadthesoftwarefollowedbyinstructionsforcreating
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 LT3754 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 5% of the full LED current.
an output voltage ‘V ’ (LT3754 CTRL pin voltage) from
OUT
a specified V supply (LT3754 V pin voltage). At any
CC
REF
WhilethisfeatureisintendedtodirectlyprotecttheLT3754,
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 LT3754 junction temperature, the
TSET function also provides some LED current derating
at high temperatures.
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.
3754fc
19
LT3754
applicaTions inForMaTion
Two external resistors program the maximum IC junction
Programming Overvoltage Protection (OVP) level
temperature using a resistor divider from the V
pin,
REF
The LT3754 LED driver provides optimum protection to
the LEDs and the external MOSFET by providing a pro-
grammablemaximumregulatedoutputvoltagelimitusing
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
the OVP
pin. The Overvoltage Protection (OVP) level
SET
Table 8 shows commonly used values for R1 and R±.
is programmed as:
OVP(MAXIMUM REGULATED V ) = 57 • OVP
OUT
SET
31
V
REF
If every LED string fails open or the multiple string LED
displaybecomesdisconnectedtheLT3754LEDdriverloop
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:
R2
R1
LT3754
30
T
SET
3754 F09
Figure 9. Programming the TSET Pin
950
900
850
800
750
700
650
600
550
500
OVP(RECOMMENDED) = 1.2 • ((N • V ) + 1V)
F
where:
N = number of LEDs in each string,
V
PTAT
V = maximum LED forward voltage drop
F
and the scaling factor of 1.± accounts for variation in the
generation of OVP from OVP pin voltage and start-up
SET
logic requirements.
0
25
50
150
75
100
125
Example:Foraconverteroperatingwith10LEDsperstring
at a maximum forward voltage of 4V per LED, the OVP
level should be programmed to:
JUNCTION TEMPERATURE (°C)
3754 F10
Figure 10. Programing the TSET Pin Threshold
OVP(RECOMMENDED)=1.2• (10 • 4)+1V = 49.2V
(
)
49.2
57
Table ꢀ. Resistor Values to Program Maximum IC Junction
Temperature (VREF (Typical) = 1.485V)
For OVP = 49.2V, OVPSET
=
= 0.863V
T (°C)
R1 (k)
±4.9
R2 (k)
±0
T
(V)
J
SET
The OVP pin voltage can be generated using a resistor
SET
100
115
130
0.8±4
0.866
0.90±
divider from the REF pin.
±8.0
±0
30.9
±0
3754fc
20
LT3754
applicaTions inForMaTion
LED Open Circuit and PWM Dimming Ratios
V
range, LED current range (if analog dimming) and
IN
temperaturerange.BeawarethatiftheV pincomponents
C
The LT3754 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
represent the dominant pole for the converter loop and
they have been adjusted to achieve stability, the V pin
C
might move more slowly during load transient conditions
such as an all-LEDs-open fault. A slower moving V pin
C
start-up when V
is low, the LT3754 ignores low LED
OUT
OUT
will add to V
overshoot during an all-LEDs-open fault.
OUT
pin voltages until V
reaches 90% of its maximum al-
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
lowed OVP level. Once this condition is met, the LT3754
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)
theLT3754onlymonitors/updatesfaultconditionsduring
PWM high(andonlyafterablankdurationof±µsfollowing
each PWM rising edge).
V to move more quickly and V
to move more slowly
C
OUT
resulting in less overshoot during an all-LEDs-open fault.
Thermal Considerations
LED Short Circuit
TheinternalpowerdissipationoftheLT3754comesfrom3
main sources: V quiescent current (I total), V current
IN
Q
IN
AshortcircuitfaultbetweenthepositiveterminalofanLED
for GATE switching (I
) and the LT3754 LED current
GATE
string (V ) and the negative terminal of the LED string
OUT
sources. Since the maximum operational V voltage is
IN
(LEDx pin) causes the channel to be disabled in order to
40V, care should be taken when selecting the switching
protect the internal current source. A resistive short is
frequency and type of external power MOSFET since the
allowed as long as (V -V
) < 6V. During the short,
OUT LEDx
current required from V for GATE switching is given by,
IN
however, cable inductance can cause the LED pin voltage
to overshoot past V voltage. To avoid LED pin voltage
I
= f
• Qg
OSC
OUT
GATE
exceeding its absolute maximum rated voltage, a diode
may be required to clamp the LED pin. The anode of a
1N4148WS diode should be connected to the LED pin and
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 LT3754. A low Q MOSFET should al-
g
the cathode of the diode connected to the V
pin. Keep
OUT
ways be used when operating the LT3754 from high V
IN
the traces as short as possible. A Schottky diode should
not be used due to high reverse bias leakage currents.
voltages. The internal junction temperature of the LT3754
can be estimated as:
Loop Compensation
T =T +[V • (I
+(f •Q ))+(16•I(LED )•1.1V)]
J
• θ
A
IN QTOTAL OSC g X
JA
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
where, T is the ambient temperature for the LT3754
A
I
representstheV quiescentcurrentfortheLT3754
QTOTAL
IN
(not switching, PWM = 1.5V and CTRL = 0.1V) - illustrated
coverarangeofV ,V ,f ,outputpowerandinductor
in the Typical Characteristics Graphs – plus the base cur-
IN OUT OSC
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
rents of active channels (typically 16 • I(LED)/75). θ is
JA
the thermal resistance of the package (34°C/W for the
5mm × 5mm QFN package).
3754fc
21
LT3754
applicaTions inForMaTion
Example : For a 1±W LED driver application requiring 16
continuous copper ground plane underneath the device to
reducedietemperatureandmaximizethepowercapability
oftheIC.Ananaloggroundisdownbondedtotheexposed
pad near the RT and V pins. I , R and V components
strings of 10 LEDs each driven with ±0mA, V = ±4V, f
IN
OSC
= 1MHz, Q (at 7V V ) = 15nC, I(LED ) = ±0mA, and an
g
GS
X
85°C ambient temperature for the LT3754 IC, the LT3754
C
SET
T
C
should be connected to an area of ground copper near
junction temperature can be approximated as:
thesepins.TheOVP trackshouldbekeptawayfromfast
SET
T = 85°C + [24 • (9.5mA + (16 • ±0mA/75) + (1MHz
J
moving signals and not loaded with an external capacitor.
GATE pin turn off currents escape through a downbond to
the exposed pad near the GATE pin. This area of copper
should be the power ground (PGND) connection for the
• 15nC)) + (16 •20mA • 1.1V)] • 34
= 85°C + [(24 • 28.8mA) + (3±0mA • 1.1V)] • 34
= 85°C + (0.691W + 0.35W) • 34
= 85°C + 35°C
inductor input capacitor, INTV capacitor and output
CC
capacitor. A separate bypass capacitor for the V pin of
IN
the IC may be required close the V pin and connected
IN
T = 1±0°C
J
to the copper area associated with analog ground. 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.
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 LT3754.
Circuit Layout Considerations
As with all switching regulators, careful attention must be
given to PCB layout and component placement to achieve
optimal thermal, electrical and noise performance. The
exposed pad of the LT3754 is the only ground connec-
tion for the IC. The exposed pad should be soldered to a
3754fc
22
LT3754
Typical applicaTions
3754fc
23
LT3754
Typical applicaTions
3754fc
24
LT3754
Typical applicaTions
31W LED Driver, 400kHz Boost, 3 Strings, 250mA per String
L1
10µH
D1
UP TO 42V OF LEDs PER STRING
V
IN
8V TO 36V
2.2µF
4.7µF
50V
100V
×10
V
IN
INTV
CC
M1
GATE
SENSE
4.7µF
10V
•
•
•
•
•
•
•
•
•
0.007Ω
100k
LT3754
1M
FAULT
V
OUT
SHDN/UVLO
LED16
232k
GND
LED1
LED2
SYNC
PWM
CTRL
LED3
LED4
LED5
PWM DIMMING
LED6
LED7
ANALOG DIMMING
LED8
LED9
LED10
LED11
LED12
LED13
LED14
LED15
V
REF
20k
T
SET
15k
OVP
I
V
C
3754 TA06
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
3754fc
25
LT3754
Typical applicaTions
14W LED Driver, ꢀ00kHz Boost, 4 Strings, 80mA per String
L1
15µH
D1
UP TO 45V OF LEDs PER STRING
12V
IN
10V TO 14V
2.2µF
100V
×5
4.7µF
25V
V
IN
INTV
CC
4.7µF
10V
M1
GATE
SENSE
V
•
•
•
•
•
•
•
•
•
•
•
•
IN
0.02Ω
LT3754
1M
100k
FAULT
V
OUT
SHDN/UVLO
GND
LED1
LED2
SYNC
LED3
LED4
LED5
PWM
CTRL
PWM DIMMING
LED6
LED7
ANALOG DIMMING
LED8
LED9
LED10
LED11
LED12
LED13
LED14
LED15
LED16
V
REF
20k
T
SET
11k
OVP
I
V
C
RT
SET
SET
3754 TA06
30.9k
20k
60.4k
14.7k 7.5k
4.7nF
L1: SUMIDA CDRH8D38
M1: VISHAY SILICONIX Si7308DN
D1: DIODES, INC. DFLS160
3754fc
26
LT3754
Typical applicaTions
•
3754fc
27
LT3754
package DescripTion
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
UH Package
32-Lead Plastic QFN (5mm × 5mm)
(Reference LTC DWG # 05-08-1693 Rev D)
0.70 ±0.05
5.50 ±0.05
4.10 ±0.05
3.45 ± 0.05
3.50 REF
(4 SIDES)
3.45 ± 0.05
PACKAGE OUTLINE
0.25 ± 0.05
0.50 BSC
RECOMMENDED SOLDER PAD LAYOUT
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
BOTTOM VIEW—EXPOSED PAD
PIN 1 NOTCH R = 0.30 TYP
OR 0.35 × 45° CHAMFER
R = 0.05
TYP
0.00 – 0.05
R = 0.115
TYP
0.75 ± 0.05
5.00 ± 0.10
(4 SIDES)
31 32
0.40 ± 0.10
PIN 1
TOP MARK
(NOTE 6)
1
2
3.45 ± 0.10
3.50 REF
(4-SIDES)
3.45 ± 0.10
(UH32) QFN 0406 REV D
0.200 REF
0.25 ± 0.05
0.50 BSC
NOTE:
1. DRAWING PROPOSED TO BE A JEDEC PACKAGE OUTLINE
M0-220 VARIATION WHHD-(X) (TO BE APPROVED)
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 0.20mm 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
3754fc
28
LT3754
revision hisTory
REV
DATE
DESCRIPTION
PAGE NUMBER
A
07/10 Updated V pin labelling
1, ±, 18, ±3, ±4, ±5, ±6
REF
Corrected electrical spec limit (V
= INTV abs max)
3
IN(MAX)
CC
Updated Electrical Characteristics conditions
Updated Typical Performance Characteristics (label)
Updated Pin Functions
3, 4, 5
7
8
Updated Operations text
10
Updated equation
13
Corrected text errors
14, 15, ±0
Updated PWM Dimming Guidelines (added items 7, 8)
Updated Figure 6
17
18
Updated LED Short Circuit text
±1
Updated Typical Applications (output capacitor formatting)
Added new Typical Application (SEPIC)
Updated Related Parts
±3, ±4, ±5
±7
30
8
B
C
01/11 Revised FAULT pin description in Pin Functions section
10/11 Updated Features section.
1
Updated “Programming LED Current Derating (Breakpoint and Slope) versus LED Ambient
Temperature (CTRL Pin)” section.
18
3754fc
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.
29
LT3754
relaTeD parTs
PART NUMBER
DESCRIPTION
COMMENTS
= 4.5V, V
LT3755/LT3755-1 High Side 40V, 1MHz LED Controller with
True Color 3,000:1 PWM Dimming
V
= 40V, V
= 60V, 3,000:1 True Color PWM Dimming,
IN(MIN)
IN(MAX)
OUT(MAX)
I
= <1µA, 3mm × 3mm QFN-16 MSOP-16E
SD
LT3756/LT3756-1 High Side 100V, 1MHz LED Controller
with True Color 3,000:1 PWM Dimming
V
SD
= 6.0V, V
= 100V, V
= 100V, 3,000:1 True Color PWM Dimming,
IN(MIN)
IN(MAX)
OUT(MAX)
I
= <1µA, 3mm × 3mm QFN-16 MSOP-16E
LT3598
LT3599
LT3595
LTC3783
LT3517
LT3518
LT3486
44V, 1.5A, ±.5MHz Boost 6-Channel
±0mA LED Driver
V
= 3V, V
SD
= 30V(40VMAX), V
OUT(MAX)
= 44V, 1,000:1 True Color PWM
= 44V, 1,000:1 True Color PWM
IN(MIN)
IN(MAX)
Dimming, I = <1µA, 4mm × 4mm QFN-±4
44V, ±A, ±MHz Boost 4-Channel 1±0mA
LED Driver
V
= 3V, V
SD
= 30V(40VMAX), V
IN(MAX) OUT(MAX)
IN(MIN)
Dimming, I = <1µA, 4mm × 4mm QFN-±4
45V, ±.5MHz 16-Channel Full Featured
LED Driver
V
SD
= 4.5V, V
= <1µA, 5mm × 9mm QFN-56
= 45V, V
= 45V, 5,000:1 True Color PWM Dimming,
IN(MIN)
IN(MAX)
OUT(MAX)
OUT(MAX)
I
High Side 36V, 1MHz LED Controller with
True Color 3,000:1 PWM Dimming
V
SD
= 3.0V, V
= 36V, V
= 40V, 3,000:1 True Color PWM Dimming,
IN(MIN)
IN(MAX)
I
= <±0µA, 4mm × 5mm DFN-16 TSSOP-16E
1.3A, ±.5MHz High Current LED Driver
with 3,000:1 Dimming
V
SD
= 3.0V, V
= <1µA, 4mm × 4mm QFN-16
= 30V, V
= 45, 3,000:1 True Color PWM Dimming,
= 45, 3,000:1 True Color PWM Dimming,
= 36V, 1,000:1 True Color PWM Dimming,
= 40V, 1,000:1 True Color PWM Dimming,
= 40V, 3,000:1 True Color PWM Dimming,
= 13.5V, 400:1 True Color PWM Dimming,
= 13.5V, 3,000:1 True Color PWM Dimming,
= 36V, 1,000:1 True Color PWM Dimming,
IN(MIN)
IN(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
I
±.3A, ±.5MHz High Current LED Driver
with 3,000:1 Dimming
V
SD
= 3.0V, V
= <1µA, 4mm × 4mm QFN-16
= 30V, V
IN(MAX)
IN(MIN)
I
Dual 1.3A, ±MHz High Current LED Driver
V
SD
= ±.5V, V
= ±4V, V
IN(MAX)
IN(MIN)
I
= <1µA, 5mm × 3mm DFN, TSSOP-16E
LT3478/LT3478-1 4.5A, ±MHz High Current LED Driver with
3,000:1 Dimming
V
SD
= ±.8V, V
= <10µA, 5mm × 7mm QFN-10
= 36V, V
IN(MAX) OUT(MAX)
IN(MIN)
I
LT3496
Triple Output 750mA, ±.1 MHz High
Current LED Driver with 3,000:1 Dimming
V
= 3.0V, V
= 30V, V
IN(MAX)
IN(MIN)
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
I
= <1µA, 4mm × 5mm QFN-±8
SD
LT3474/LT3474-1 36V, 1A (I ), ±MHz, Step-Down
V
= 4.0V, V
IN(MAX)
= 36V, V
= 36V, V
= 16V, V
LED
LED Driver
IN(MIN)
I
= <1µA, TSSOP16E
SD
LT3475/LT3475-1 Dual 1.5A(I ), 36V, ±MHz, Step-Down
V
= 4.0V, V
LED
IN(MIN) IN(MAX)
LED Driver
I
= <1µA, TSSOP±0E
SD
LT3476
Quad Output 1.5A, ±MHz High Current
LED Driver with 1,000:1 Dimming
V
SD
= ±.8V, V
= <10µA, 5mm × 7mm QFN-10
IN(MIN) IN(MAX)
I
3754fc
LT 1011 REV C • PRINTED IN USA
30 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
LINEAR TECHNOLOGY CORPORATION 2009
(408) 43±-1900 FAX: (408) 434-0507 www.linear.com
相关型号：
LT3755EMSE#PBF
LT3755/LT3755-1/LT3755-2 - 40VIN, 75VOUT LED Controllers; Package: MSOP; Pins: 16; Temperature Range: -40°C to 85°C
Linear
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