LT3754 [Linear]
16-Channel × 50mA LED Driver; 16通道× 50毫安LED驱动器型号: | LT3754 |
厂家: | Linear |
描述: | 16-Channel × 50mA LED Driver |
文件: | 总28页 (文件大小:324K) |
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
n
±2.8% LED Current Matching at 20mA (Typ 0.ꢀ%ꢁ
n
Up to 3000:1 True Color PWM™ Dimming Range
n
Single Resistor Sets LED Current (10mA to 50mAꢁ
n
LED Current Regulated Even for PV > V
IN
OUT
n
n
n
n
n
n
current. Output voltage adapts to variations in LED V for
Output Adapts to LED V for Optimum Efficiency
F
F
optimum efficiency and open LED faults do not affect the
Fault Flag + Protection for Open LED Strings
operation of connected LED strings.
Protection for LED Pin to V
Short
OUT
Parallel Channels for Higher LED Current
Programmable LED Current Derating vs Temperature
Accurate Undervoltage Lockout Threshold with
Programmable Hysteresis
TheLT3754allowsaPWMdimmingrangeupto3000:1and
an analog dimming range up to ±5:1. Operating frequency
can be programmed from 100kHz up to 1MHz using a
single resistor or synchronized to an external clock.
n
n
Programmable Frequency (100kHz to 1MHz)
Synchronizable to an External Clock
Additional features include: programmable maximum
V
OUT
for open LED protection, a fault flag for open LED,
APPLICATIONS
programmable LED current derating vs temperature,
micropower shutdown and internal soft-start. The LT3754
is available in a thermally enhanced 5mm × 5mm 3±-pin
QFN Package.
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 Averageꢁ
92% Efficient, 36W Backlight LED Driver
PV
IN
±4V
4.7μF
4.7μF
0.ꢀ
10μH
UP TO 45V OF LEDs PER STRING
V
IN
10V
5s
±.±μF
V
IN
0.4
0.0
INTV
GATE
CC
4.7μF
499k
• • • •
SENSE
SHDN/UVLO
0.015Ω
40.±k
•
•
•
•
•
•
•
•
•
•
CTRL
V
OUT
–0.4
–0.ꢀ
LT3754
PWM
REF
LED1
LED±
•
•
R
= 14.7k (I(LED) = ±0mA)
ISET
16 CHANNELS
•
•
•
•
•
•
–50 –±5
0
±5
50 75
100 1±5
±0k
LED15
JUNCTION TEMERATURE (°C)
T
SET
LED16
3754 TA01
3754 TA01
V
IN
100k
30.9k 11k
±0k
FAULT
OVP
SET
GND RT
I
V
SYNC
SET
C
39.±k 5.76k
10k
±.±nF
3754f
1
LT3754
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1ꢁ
TOP VIEW
V
, LED1-16 .........................................................60V
OUT
V , SHDN/UVLO, FAULT...........................................40V
IN
INTV ......................................................................13V
CC
3± 31 30 ±9 ±ꢀ ±7 ±6 ±5
INTV above V ...................................................+0.3V
CC
IN
LED1
LED±
LED3
LED4
LED5
LED6
LED7
LEDꢀ
LED16
LED15
LED14
1
±
3
4
5
6
7
ꢀ
±4
±3
±±
PWM, CTRL, SYNC .....................................................6V
V ...............................................................................3V
C
REF
±1 LED13
±0 LED1±
V
, RT, I , T , OVP .......................................±V
SET SET SET
33
SENSE......................................................................0.4V
19
1ꢀ
17
LED11
LED10
LED9
Operating Junction Temperature Range
(Notes ±,3)...........................................−40 °C to 1±5 °C
Storage Temperature Range.................−65 °C to 150 °C
9
10 11 1± 13 14 15 16
UH PACKAGE
3±-LEAD (5mm s 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
TEMPERATURE RANGE
LT3754EUH#TRPBF
LT3754IUH#TRPBF
–40°C to 1±5°C
–40°C to 1±5°C
3±-Lead (5mm × 5mm) Plastic QFN
3±-Lead (5mm × 5mm) Plastic QFN
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/
3754f
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
l
l
V
V
= INTV (Shorted)
4.±
5.5
4.5
6.0
V
V
IN
IN
CC
≠ INTV
CC
Operational V
V
V
= INTV (Shorted)
4.5
6
14
40
V
V
IN
IN
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
1–16
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
1.53ꢀ
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
1.4ꢀ5
0.01
±
1.5±4
0.05
V
8/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
8/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.ꢀ
3.4
57
Dropout (V − INTV
)
CC
INTVCC
IN
(Start Switching)
(Stop Switching)
INTV UVLO (+)
CC
V
INTV UVLO (−)
CC
l
INTV Current Limit
44
mA
CC
OVP/ LED ERROR AMPLIFIERS
Transconductance (OVP)
Voltage Gain (OVP)
ΔI = ±±.5μA
VC
4
5
μmhos
V/V
Transconductance (LED)
ΔI = ±±.5μA
VC
33
μmhos
3754f
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
μS
V
Voltage Gain (LED)
V Source Current (Out of Pin)
C
V = 1.5V, V
= 0.ꢀV, OVP = 1.5V
10
C
LEDx
LEDx
LEDx
SET
V Sink Current (OVP)
C
V = 1.5V, V
= 0.ꢀV, 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.ꢀ
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
46
90
60
ΔV(V )/ΔV(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
8
SET
LEDx Current (±0mA) (R
= 14.7k)
V
V
V
= 1V, CTRL = 1.5V
= 1V, CTRL = 1.5V
= 1V, CTRL = 0.04V
19.±9
47.ꢀ5
±1.11
±±.ꢀ
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
LEDx
= 1V, CTRL = 0.04V
0.ꢀ
mA
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
Pin Current in PWM Mode V(V ) = 60V
PWM = 1.5V, V = 1V
LEDx
370
±0
μA
μA
OUT
OUT
PWM = 0V, V
= 1V
LEDx
LEDx Leakage Current
(PWM = 0V)
V
V
= 1V, V
= 1±V
= 60V
0.1
0.1
1
±
μA
μA
LEDx
LEDx
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
V
= 1±V
= 60V
6
6
x
SH
OUT
OUT
(V
– V
)
OUT
LEDx
LED Open Detection Threshold
V
OUT
= 1±V
0.5
V
3754f
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
= 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
OUT
Over Voltage Protection (OVP) Regulation Voltage
OVP = 0.±±V
1±.5
57
V
V
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 108 and 908
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 Averageꢁ
0.ꢀ
0.4
±1.00
±0.50
±0.00
19.50
19.00
55
50
45
40
35
30
±5
±0
15
10
5
R
=
R
= 14.7k
ISET
ISET
5.76k
7.3±k
9.76k
14.7k
±9.4k
0.0
–0.4
R
ISET
= 14.7k (I(LED) = ±0mA)
–0.ꢀ
0
–50 –±5
0
±5
50 75
100 1±5
–50 –±5
0
±5
50
75 100 1±5
0.00 0.±5 0.50 0.75 1.00 1.±5 1.50
JUNCTION TEMERATURE (°C)
JUNCTION TEMERATURE (°C)
CTRL (V)
3754 G01
3754 G0±
3754 G03
3754f
5
LT3754
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
LED Current Waveforms
SHDN/UVLO Threshold
3000:1 PWM Dimming (100Hzꢁ
VREF vs Junction Temperature
vs Junction Temperature
1.5±5
1.505
1.5±5
1.505
1.4ꢀ5
1.465
1.445
I(LEDx)
±0mA/DIV
1.4ꢀ5
1.465
I(L)
1A/DIV
PWM
10V/DIV
3754 G04
5μs/DIV
1.445
–50 –±5
0
±5
50
75 100 1±5
–50 –±5
0
±5
50
75 100 1±5
JUNCTION TEMERATURE (°C)
JUNCTION TEMPERATURE (°C)
3754 G06
3754 G05
SHDN/UVLO Pin (Hysteresisꢁ
Current vs Junction Temperature
VIN Shutdown Current
vs Junction Temperature
VIN Quiescent Current vs VIN
±.ꢀ0
±.70
±.60
±.50
±.40
5
4
3
±
1
0
1±
10
ꢀ
V
= 6V, SHDN/UVLO = 0V
R
= 14.7k
IN
ISET
PWM = 1.5V, NO SWITCHING,
V(LED ) = 1.±V, CTRL = 0.1V
1-16
6
4
PWM = 0V, CTRL = 0.1V
±
±.30
±.±0
0
–50 –±5
0
±5
50
75 100 1±5
–50 –±5
0
±5
50
75 100 1±5
0
5
10 15 ±0 ±5 30 35 40
JUNCTION TEMPERATURE (°C)
JUNCTION TEMPERATURE (°C)
V
(V)
IN
3754 G07
3754 G0ꢀ
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
±.5
±.0
1.5
1.0
0.5
V
C
HIGH CLAMP
V
IN
= 6V, R
= 14.7k, CTRL = 0.1V
ISET
V
ACTIVE (SWITCHING)
PWM = 1.5V, NO SWITCHING,
V(LED ) = 1.±V, CTRL = 0.1V
C
1000
950
1-16
RT = 39.±k
5
0
V
C
LOW CLAMP
PWM = 0V, CTRL = 0.1V
900
0.0
–50 –±5
0
±5
50
75 100 1±5
–50 –±5
0
±5
50
75 100 1±5
–50 –±5
0
±5
50
75 100 1±5
JUNCTION TEMPERATURE (°C)
JUNCTION TEMPERATURE (°C)
JUNCTION TEMPERATURE (°C)
3754 G10
3754 G11
3754 G1±
3754f
6
LT3754
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
INTVCC
INTVCC
INTVCC, UVLO(+ꢁ, UVLO(–ꢁ
vs Junction Temperature
vs Current, Junction Temperature
vs Current, Junction Temperature
7.0
6.9
6.ꢀ
6.7
6.6
6.0
5.5
ꢀ
7
6
5
4
3
±
V
= 6V, PWM = 0V
V
= 1±V
I
= 10mA, ±0mA, 30mA
IN
IN
LOAD
INTV (REGULATED)
CC
INTV UVLO(+)
CC
I
= 40mA
5.00
4.5
LOAD
50
I
I
I
I
= 10mA
= ±0mA
= 30mA
= 40mA
LOAD
LOAD
LOAD
LOAD
INTV UVLO(–)
CC
V
= ꢀV, PWM = 0V
IN
–50 –±5
0
±5
75 100 1±5
–50 –±5
0
±5
50
75 100 1±5
–50 –±5
0
±5
50
75 100 1±5
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 (OVPꢁ
Level vs Junction Temperature
60
55
50
60.0
57.5
55.0
5±.5
50.0
47.5
45.0
4±.5
40.0
70
60
50
40
30
±0
10
0
V
= 6V, INTV = 0V
CC
IN
OVP
= 1.0V
SET
INDUCTOR PEAK CURRENT THRESHOLD
(CYCLE-BY-CYCLE)
45
OVP
= 0.±±V
50
SET
40
–50 –±5
0
±5
50
75 100 1±5
–50 –±5
0
±5
50
75 100 1±5
–50 –±5
0
±5
75 100 1±5
JUNCTION TEMPERATURE (°C)
JUNCTION TEMPERATURE (°C)
JUNCTION TEMPERATURE (°C)
3754 G16
3754 G17
3754 G1ꢀ
VOUT − V(LEDxꢁ Short Threshold
vs Junction Temperature
Minimum ON and OFF Times
vs Junction Temperature
GATE Rise/Fall Times
vs GATE Capacitance
7.00
6.75
±50
±±5
±00
175
150
1±5
100
1±0
100
ꢀ0
60
40
±0
0
V
= ꢀV, INTV = 7V, RT = 5±3k
C
= 3300pF
IN
CC
GATE
6.50
6.±5
MINIMUM ON-TIME
MINIMUM OFF-TIME
V
V
= 60V
= 1±V
OUT
OUT
FALL TIME
6.00
5.75
RISE TIME
5.50
5.±5
5.00
–50 –±5
0
±5
50
75 100 1±5
–50 –±5
0
±5
50
75 100 1±5
0
5
10
(nF)
15
±0
JUNCTION TEMPERATURE (°C)
JUNCTION TEMPERATURE (°C)
C
L
3754 G1ꢀ
3754 G±0
3754 G±1
3754f
7
LT3754
PIN FUNCTIONS
LED (Pin1-8,1ꢀ-24ꢁ:16LEDDriverOutputs.Eachoutput
RT (Pin 25ꢁ: 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
V (Pin 26ꢁ: Output of Both Transconductance Error
C
a single resistor at the I
pin. Channel matching is
SET
Amplifiers for the Converter Regulation Loop. The most
±±8 with an absolute current accuracy of ±38. Connect
commonly used gm error amplifier (LED) regulates V
OUT
the cathode of each LED string to an LED pin. Connect
to ensure no LED pin falls below 1V. The other gm error
the anode of each LED string to V . Channels can be
OUT
amplifier (OVP) is activated if all LEDs fail open and a
paralleled for greater LED current or individually disabled
regulated maximum V
is required. Connect a resistor
OUT
(connect LED to V ).
OUT
and capacitor in series from the V pin to ground.
C
SENSE (Pin 9ꢁ: The Current Sense Input for the Control
Loop. Connect this pin to the sense resistor in the source
of the external power MOSFET.
PWM(Pin2ꢀꢁ:InputPinforPWMDimmingControl.Above
1.4V allows converter switching and below 0.7V disables
switching. The PWM signal can be driven from 0V to 6V.
GATE (Pin 10ꢁ: Drives the gate of an N-channel MOSFET
If unused, connect to V
REF.
from 0V to INTV .
CC
OVP
(Pin 28ꢁ: Programs maximum allowed V
OUT
SET
INTV (Pin 11ꢁ: A 7V LDO supply generated from V and
regulation level if all LEDs are open circuit.
CC
IN
used to power the GATE driver and some control circuitry.
CTRL (Pin 29ꢁ: CTRL pin voltage below 1V controls
Must be bypassed with a 4.7μF capacitor to GND.
maximum LED current. CTRL voltage can be set by a
V (Pin 12ꢁ: Input Supply Pin. Must be locally bypassed
resistordividerfromV ,V oranexternalvoltagesource.
IN
IN REF
with a 1μF capacitor to ground.
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
SHDN/UVLO(Pin13ꢁ: TheSHDN/UVLOpinhasanaccurate
1.476Vthresholdandcanbeusedtoprogramanundervoltage
lockout (UVLO) threshold for system input supply using
a resistor divider from supply to ground. A ±.4μA pin
currenthysteresisallowsprogrammingofUVLOhysteresis.
SHDN/UVLO above 1.476V turns the part on and removes
a ±.4μA sink current from the pin. SHDN/UVLO < 0.7V
from V pin with temperature dependent resistance.
REF
T
(Pin 30ꢁ: Programs LT3754 junction temperature
SET
breakpoint past which LED current will begin to derate.
V
(Pin 31ꢁ: 1.4ꢀ5V Reference Output Pin. This pin
REF
can supply up to 150μA. Can be used to program CTRL,
reducesV current<±0μA.Iftheshutdownfunctionisnot
IN
T
SET
and OVP pin voltages using resistor dividers to
SET
required, it should be forced above 1.476V or connected
ground.
directly to V .
IN
I
(Pin32ꢁ:ResistortoGroundProgramsLEDpincurrent.
SET
FAULT (Pin 14ꢁ: Active low if any or all LED strings have
an open fault or if any/all LED pins have been shorted to
See Table 6 in the Applications Information Section.
Exposed Pad (Pin 33ꢁ: 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.Pin33shouldbesolderedtoacontinuouscopper
ground plane under the device to reduce die temperature
and increase the power capability of the LT3754.
V
. If fault(s) removed, FAULT flag returns high. Fault
OUT
status is only updated during PWM high state and latched
during PWM low.
SYNC(Pin15ꢁ:Allowssynchronizationofboostconverter
switchingfrequencytoanexternalclock.RTresistorshould
be programmed for f
±08 below SYNC frequency. If
OSC
unused, connect to GND.
V
(Pin16ꢁ: 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
3754f
8
LT3754
BLOCK DIAGRAM
1±
11
SHDN/UVLO
V
INTV
CC
7V(REGULATED)
UVLO(ꢀ) = 3.ꢀV, UVLO(ꢁ) = 3.4V
IN
13
+
R
S
1.476V
–
GATE
10
Q
600k
V
C
SYNC
15
EN
+
–
+
–
OSC
RT
SLOPE
±5
–
+
–
+
1.4ꢀ5V
5±mV
100mV
OVER
CURRENT
REF
1.4ꢀ5V
+
–
PEAK
4.±V(ꢀ)
3.7V(ꢁ)
CURRENT
SENSE
9
EN
HICCUP__MODE
V
OUT
INTV
CC_UV
IN_UV
SHDN_UV
16
+
–
6V
V
LEDx
1-ꢀ, 17-±4
PWM
EN
FAULT
SOFT
START
±7
31
14
V
REF
EN
LED
LOGIC
SS
1V
+
+
+
–
CTRL
±9
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
3±
33
±6
±ꢀ
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
for the top (anode) of all LED strings. LED string
OUT
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
REF
and INTV , are generated by the LT3754. The V
CC REF
pinprovidesaprecision1.4ꢀ5Voutputforusewithexternal
resistors to program the CTRL, OVP
and T
input
SET
SET
pins. The INTV pin provides a regulated 7V output to
CC
between 10mA to 50mA using a single resistor at the I
SET
supply the gate driver for the boost controller GATE pin.
An accurate 1.476V threshold on the SHDN/UVLO pin
combinedwithaSHDN/UVLOpincurrenthysteresisallows
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
IN
LED pin to V
before startup). For optimum efficiency,
OUT
3754f
9
LT3754
OPERATION
to define the turn on/off voltages for V . SHDN/UVLO pin
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.
TheLT3754constantswitchingfrequencyisprogrammable
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.ꢀA 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.
outputvoltageV usingasingleinductor,Schottkydiode
OUT
For robust operation the LT3754 monitors system
conditions and performs soft start for startup after any of
and output capacitor. With LED strings connected from
V
to every LED pin, the lowest voltage on each LED pin
OUT
the following faults: V , SHDN or INTV voltages too low
IN
CC
is monitored and compared to an internal 1V reference.
is regulated to ensure the lowest LED pin voltage of
or MOSFET current too high. The LT3754, when entering
these faults, discharges an internal soft start node and
prevents switching at the GATE pin. When exiting these
faults the LT3754 ramps up an internal soft start node to
V
OUT
any connected LED string is maintained at 1V. If any of
the LED strings are open, the LT3754 will ignore the open
LED pin. If all of the LED strings are open V
charges up
OUT
controlV pinvoltageriseandhencecontrolMOSFETpeak
C
until 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.
switchcurrentrise.Inadditionthesoftstartperiodgradually
ramps up switching frequency from approximately 338
to 1008 of full scale.
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 508. Any
over current fault condition in the MOSFET turns off the
MOSFETandtriggerssoftstartinternally.Inthisfaultmode
The LT3754 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
3754f
10
LT3754
APPLICATIONS INFORMATION
INTV Regulator Bypassing and Operation
Inductor
CC
The INTV pin is the output of an internal linear regulator
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
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(assuming508inductorripplecurrent
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.ꢀV
CC
and maintains switching until INTV falls below 3.4V.
CC
1
VOUT
1
fOSC
This feature prevents excessive power dissipation in the
1−
•
• VIN
external MOSFET by ensuring a minimum gate drive level
V
V
to keep R
low. The INTV regulator has a current
CC
IN
DS(ON)
L =
limit of 44mA to limit power dissipation inside the I.C.
Thiscurrentlimitshouldbeconsideredwhenchoosingthe
N-channel power MOSFET and the switching frequency.
0.5• OUT •ILEDx •16
V
IN
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
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
LT3754 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 16
strings of 10 LEDs each driven with ±0mA, and choos-
power dissipation from the LT3754 and/or to remove the
INTV current limitation of 44mA. An external supply for
ing V = 1±V, V
= (3.75V • 10) + 1V = 3ꢀ.5V, I
=
CC
CC
IN
OUT
LEDx
INTV should never exceed the V pin voltage or the
±0mA 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
3.2
1
to the V pin, V operational range is 4.5V to 13V.
IN
(1−
)•
•12V
106
L =
= 16.5μH
0.5•3.2•20mA •16
3754f
11
LT3754
APPLICATIONS INFORMATION
Table 1. Inductor Manufacturers
Schottky Rectifier
MANUFACTURER
Sumida
PHONE NUMBER
40ꢀ-3±1-9660
605-ꢀꢀ6-43ꢀ5
40±-563-6ꢀ66
ꢀ47-639-6400
561-99ꢀ-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
exceedtheapplication’saverageoutputcurrent.Thediode’s
maximum reverse voltage must exceed the maximum
output voltage of the application. For PWM dimming
applicationsbeawareofthereverseleakageoftheSchottky
diode.Lowerleakagecurrentwilldraintheoutputcapacitor
less during PWM low periods, allowing for higher PWM
dimming ratios. The companies below offer Schottky
diodes with high voltage and current ratings.
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
ꢀ05-446-4ꢀ00
ꢀꢀꢀ-743-7ꢀ±6
631-360-±±±±
40±-563-6ꢀ66
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
40ꢀ-9ꢀ6-04±4
ꢀ14-±37-1431
40ꢀ-573-4150
ꢀ43-44ꢀ-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
OSC
GATE
g
Murata
Taiyo Yuden
AVX
www.avxcorp.com
3754f
12
LT3754
APPLICATIONS INFORMATION
In addition, the current drive required for GATE switching
52mV •0.7
IL(PEAK)
RS≤
should also be kept low in the case of high V voltages
IN
(see“ThermalConsiderations”intheApplicationsInforma-
where
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
1−D
0.5
2
IL(PEAK)
=
•16 •I • 1+
LEDx ⎟ ⎜
⎜⎜
⎟
⎠
⎟
⎝
⎛
⎞
VOUT(MAX)
⎜
⎜
⎝
⎟
⎟
⎠
D= MOSFET duty cycle=
VOUT(MAX) = N• V
,
VIN(MIN)
+ 1V
(
)
F(MAX)
Table 4. MOSFET Manufacturers
N= number of LEDs in each string,
MANUFACTURER
PHONE NUMBER
WEB
Vishay Siliconix
40±-563-6ꢀ66
www.vishay.com
www.irf.com
VF(MAX)= maximum LED forward voltage drop,
VIN(MIN)= minimum input voltage to the inductor,
International Rectifier 310-±5±-7105
Fairchild 97±-910-ꢀ000
www.fairchildsemi.com
andthe0.5termrepresentsaninductorpeak-to-peakripple
current of 508 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 50mV 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
= ꢀV, V
= (4V • 10)+1V = 41V and I
IN(MIN)
OUT(MAX) LEDx
= ±0mA, the value for RS is chosen as:
52mV • 0.7
IL(PEAK)
52mV • 0.7
RS ≤
≤
⎛
⎜
⎞
41
⎝ 8
• 16 • 0.02 • 1+ 0.25
⎟
(
)
⎠
52mV • 0.7
2.05
≤
≤ 17.7 mΩ
3754f
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 startup or recovery from a fault condition, the
LT3754 provides a soft start function. The LT3754
when entering these faults will discharge an internal
soft start node and prevent switching at the GATE
should be recalculated for the chosen RS value to ensure
the chosen inductor will not saturate.
Power MOSFET: Overcurrent and Hiccup Mode
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,
pin for any of the following faults: V , SHDN/UVLO
IN
or INTV
voltages too low or MOSFET current
CC
toohigh(seethetimingdiagraminFigure±).Whenexiting
thesefaultstheLT3754rampsupaninternalsoftstartnode
atapproximately0.5V/mstocontrolV pinvoltageriseand
C
hence control MOSFET switch current rise. In addition the
soft start period gradually ramps up switching frequency
from approximately 338 to 1008 of full scale.
100mV
RS
ID(OVERCURRENT)
=
The conditions required to exit all faults and allow a soft
start ramp of the VC pin are listed in Figure ±. An added
feature of the LT3754 is that it waits for the first PWM pin
active high (minimum ±00ns pulse width) before it allows
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.
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 r 4.2V,
SHDN > 1.476V, INTV > 3.8V,
CC
V
< 3.7V, SHDN < 1.476V,
IN
I
(EXTERNAL MOSFET) < 100mV/RS,
DSS
INTVCC < 3.4V
(EXTERNAL MOSFET) > 100mV/RS
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
3754f
14
LT3754
APPLICATIONS INFORMATION
the soft start of VC pin to begin. This feature ensures that
during startup of the LT3754 the soft start ramp has not
timed out before PWM is asserted high. Without this ‘wait
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 :
forPWMhigh’feature,systemswhichapplyPWMafterV
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
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
ꢀ00
700
600
500
V
SUPPLY
R1
R±
SHDN/UVLO
13
–
+
600k
1.476V
400
300
±00
OFF ON
100
0
100
±00
300
400
500
600
RT (kΩ)
3754 F04
3754 F03
Figure 3. Programming Undervoltage
Lockout (UVLOꢁ with Hysteresis
Figure 4. Switching Frequency vs RT
3754f
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% resistorsꢁ
R
ISET
(kΩꢁ
LED Current per CHANNEL (mAꢁ
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% resistorsꢁ
SWITCHING FREQUENCY (kHzꢁ
RT (kΩꢁ
5±3
100
±00
300
400
500
600
700
ꢀ00
900
1000
±49
15ꢀ
Synchronizing to an external clock
115
The SYNC pin allows the LT3754 oscillator to be
synchronized 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
synchronization, the free running oscillator frequency
90.9
73.±
60.4
51.1
44.±
39.±
Duty Cycle Considerations
(f ) of the LT3754 should be programmed to ꢀ08 of
OSC
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
programmed 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.
3754f
16
LT3754
APPLICATIONS INFORMATION
Analog Dimming
T
PWM
ON(PWM)
(= 1/f
)
PWM
T
TheLT3754allowsforLEDdimming(brightnessreduction)
byanalogdimmingorbyPWMdimming. 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
Some general guidelines for LED current dimming using
the PWM pin (see Figure 5):
REF
source. If analog dimming is not required, the pin can be
directly connected to the V pin. The only drawback of
REF
(1) PWM Dimming Ratio (PDR) = 1/(PWM Duty Cycle) =
analog dimming is that reducing LED current to reduce
the brightness of the LED also changes the perceived
color of the LED.
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 ꢀ0Hz)
PWM Dimming
Many applications require an accurate control of the
brightnessoftheLED(s).Inaddition,beingabletomaintain
a constant color over the entire dimming range can be just
as critical. For constant color LED dimming the LT3754
providesaPWMpinandspecialinternalcircuitrytoachieve
uptoa3000:1widePWMdimmingrange. 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
(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
(6)ChoosetheSchottkydiodefortheLT3754boostconverter
for minimum reverse leakage current.
See “LED Current vs PWM Duty Cycle” in the Typical
Performance Characteristics section.
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.
3754f
17
LT3754
APPLICATIONS INFORMATION
Programming LED Current Derating (Breakpoint and
Slopeꢁ versus LED Ambient Temperature (CTRL Pinꢁ
divider with temperature dependent resistance (Figures 7
and ꢀ). A variety of resistor networks and NTC resistors
with different temperature coefficients can be used to
achieve the desired CTRL pin voltage behaviour versus
temperature. The current derating curve in Figure 6 uses
the resistor network shown in option C of Figure 7.
LED datasheets 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
allowingtheprogrammingofanLEDcurrentderatingcurve
versustheambienttemperatureoftheLED(s).Withoutthe
ability to back off LED currents as temperature increases,
many LED drivers are limited to driving the LED(s) at 508
orlessoftheirmaximumratedcurrents.TheLT3754allows
the temperature breakpoint and the slope of LED current
versus ambient temperature to be programmed using a
simple resistor network shown in Figure 7.
Table 7 shows a list of NTC resistor manufacturers/
distributors. There are several other manufacturers
available and the chosen supplier should be contacted
for more detailed information. To use an NTC resistor to
monitor the ambient temperature of the LED(s) it should
be placed as close as possible to the LED(s). Since the
temperature dependency 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.
Without the ability to back off LED current as the ambient
temperatureoftheLED(s)increases,manyLEDdriversare
limited to driving the LED(s) at only 508 or less of their
maximum rated currents. This limitation requires more
LEDstoobtaintheintendedbrightnessfortheapplication.
The LT3754 allows the LED(s) to be programmed for
maximum allowable current while still protecting the
LED(s) from excessive currents at high temperature. This
is achieved by programming a voltage at the CTRL pin
with a negative temperature coefficient using a resistor
Table ꢀ. NTC Resistor Manufacturers
MANUFACTURER
Murata Electronics North America
TDK Corporation
WEB
www.murata.com
www.tdk.com
www.digikey.com
Digi-key
±50
31
REF
R1
±±5
LT3754
RESISTOR
OPTION A
29
CTRL
±00
175
R2
OPTION A TO D
LT3754
PROGRAMMED LED
CURRENT DERATING
150
CURVE
R
R
Y
Y
1±5
100
R
R
R
R
R
NTC
R
X
NTC
NTC
X
NTC
–50 –±5
0
±5
50
75 100 1±5
T -TEMPERATURE (°C)
A
3754 F06
A
B
C
D
3754 F07
Figure 6. LED Current Derating vs LED Ambient Temperature
Figure ꢀ. Programming LED Current Derating Curve
vs Ambient Temperature (RNTC Located on LED PCBꢁ
3754f
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.±5
1.00
RESISTOR
OPTION A
0.75
0.50
0.±5
0
10 ±0 30 40 50 60 70 ꢀ0
- AMBIENT TEMPERATURE (°C)
T
A
3754 F0ꢀ
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
Simulator’,userscanlogontowww.murata.com/designlib
and download the software followed by instructions for
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 58 of the full LED current.
creatinganoutputvoltage‘V ’(LT3754CTRLpinvoltage)
from a specified V supply (LT3754 V pin voltage). At
OUT
CC
REF
WhilethisfeatureisintendedtodirectlyprotecttheLT3754,
it can also be used to derate the LED current at high
temperatures. Since there is a direct relationship between
theLEDtemperatureandLT3754junctiontemperature,the
TSET function also provides some LED current derating
at high temperatures.
any 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 LT347ꢀ LED driver
data sheet section Programming LED Current Derating vs
Temperature under Applications Information.
3754f
19
LT3754
APPLICATIONS INFORMATION
Two external resistors program the maximum IC junction
Programming Overvoltage Protection (OVPꢁ 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
programmable maximum regulated output voltage limit
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
using the OVP pin. The Overvoltage Protection (OVP)
SET
Table ꢀ shows commonly used values for R1 and R±.
level 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:
R±
R1
LT3754
30
T
SET
3754 F09
Figure 9. Programming the TSET Pin
950
900
ꢀ50
ꢀ00
750
700
650
600
550
500
OVP(RECOMMENDED) = 1.± • ((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
logic requirements.
pin voltage and startup
SET
0
±5
50
150
75
100
1±5
Example:Foraconverteroperatingwith10LEDsperstring
at a maximum forward voltage of 4V per LED, the OVP
level should be programmed to:
JUNCTION TEMPERATURE (°C)
359ꢀ 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 (Typicalꢁ = 1.485Vꢁ
For OVP= 49.2V, OVPSET
=
= 0.863V
T (°Cꢁ
R1 (kꢁ
±4.9
R2 (kꢁ
±0
T
(Vꢁ
SET
J
The OVP pin voltage can be generated using a resistor
SET
100
115
130
0.ꢀ±4
0.ꢀ66
0.90±
divider from the REF pin.
±ꢀ.0
±0
30.9
±0
3754f
20
LT3754
APPLICATIONS INFORMATION
LED Open Circuit and PWM Dimming Ratios
more slowly during load transient conditions such as an
all-LEDs-openfault.AslowermovingV pinwilladdtoV
C
OUT
The LT3754 monitors each LED pin voltage to determine if
the LED string has an open fault (LED pin voltage < 0.5V).
IfanopenLEDfaultoccurs, theFAULTflagispulledlow. To
avoid false detection of faults during the initial converter
overshoot during an all-LEDs-open fault. An alternative
compensation approach is to place the dominant pole of
theconverterloopattheoutput.Thisrequiresanincreased
output capacitor value but will allow a much reduced Vc
startup when V
is low, the LT3754 ignores low LED
OUT
OUT
capacitor. The combination will allow V to move more
C
pin voltages until V
reaches 908 of its maximum
quickly and V
to move more slowly resulting in less
overshoot during an all-LEDs-open fault.
OUT
allowed 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)
the LT3754 only monitors/updates fault conditions during
PWMhigh(andonlyafterablankdurationof±μsfollowing
each PWM rising edge).
Thermal Considerations
TheinternalpowerdissipationoftheLT3754comesfrom3
main sources: V quiescent current (I total), V current
IN
Q
IN
for GATE switching (I
) and the LT3754 LED current
GATE
sources. Since the maximum operational V voltage is
IN
LED Short Circuit
40V, care should be taken when selecting the switching
frequency and type of external power MOSFET since the
A short circuit fault between the positive terminal of an
current required from V for GATE switching is given by,
IN
LED string (V ) and the negative terminal of the LED
OUT
string (LEDx pin) causes the channel to be disabled in
I
= f
• Qg
GATE
OSC
order to protect the internal current source. A resistive
where Q is the gate charge (at V = INTV ) specified
g
GS
CC
short is allowed as long as (V -V
) < 6V.
OUT LEDx
for the MOSFET and f
is the programmed switching
OSC
frequency for the LT3754. A low Q MOSFET should
g
Loop Compensation
always be used when operating the LT3754 from high V
IN
Be sure to check the stability of the loop with the LEDs
connected (LED regulation loop) and disconnected
(Overvoltage Protection (OVP) regulation loop). Various
applicationcircuitsareshowninthedatasheetwhichcovera
voltages. The internal junction temperature of the LT3754
can be estimated as:
T =T +[V •(I
+(f •Q ))+(16•I(LED )•1.1V)]
OSC g X
J
• θ
A
IN QTOTAL
JA
rangeofV ,V ,f ,outputpowerandinductorcurrent
IN OUT OSC
ripple values. For application requirements which deviate
where, T is the ambient temperature for the LT3754
A
from the circuits shown in the datasheet be sure to check
I
representstheV quiescentcurrentfortheLT3754
QTOTAL
IN
the stability of the final application over the full V range,
(not switching, PWM = 1.5V and CTRL = 0.1V) - illustrated
IN
LED current range (if analog dimming) and temperature
in the Typical Characteristics Graphs – plus the base
range. Be aware that if the V pin components represent
currents of active channels (typically 16 • I(LED)/75). θ
JA
C
the dominant pole for the converter loop and they have
is the thermal resistance of the package (34°C/W for the
been adjusted to achieve stability, the V pin might move
5mm × 5mm QFN package).
C
3754f
21
LT3754
APPLICATIONS INFORMATION
Example : For a 1±W LED driver application requiring 16
copper ground plane underneath the device to reduce die
temperature and maximize the power capability of the IC.
Ananaloggroundisdownbondedtotheexposedpadnear
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
ꢀ5°C ambient temperature for the LT3754 IC, the LT3754
the RT and V pins. I , R and V components should
C SET T C
junction temperature can be approximated as:
be connected to an area of ground copper near these
pins. The OVP track should be kept away from fast
SET
T = ꢀ5°C + [±4 • (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 •±0mA • 1.1V)] • 34
= ꢀ5°C + [(±4 • ±ꢀ.ꢀmA) + (3±0mA • 1.1V)] • 34
= ꢀ5°C + (0.691W + 0.35W) • 34
= ꢀ5°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
T = 1±0°C
J
IN
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
exposedpadoftheLT3754istheonlygroundconnectionfor
theIC.Theexposedpadshouldbesolderedtoacontinuous
3754f
22
LT3754
TYPICAL APPLICATIONS
3754f
23
LT3754
TYPICAL APPLICATIONS
3754f
24
LT3754
TYPICAL APPLICATIONS
31W LED Driver, 400kHz Boost, 3 Strings, 250mA Per String
L1
10μH
D1
UP TO 4±V OF LEDs PER STRING
V
IN
ꢀV TO 36V
10 s
4.7μF
50V
±.±μF
100V
V
IN
INTV
CC
M1
GATE
SENSE
4.7μF
10V
•
•
•
•
•
•
•
•
•
0.007Ω
100k
LT3754
1M
FAULT
V
OUT
SHDN/UVLO
LED16
±3±k
GND
LED1
LED±
SYNC
PWM
LED3
LED4
LED5
PWM DIMMING
LED6
LED7
ANALOG DIMMING
CTRL
REF
LEDꢀ
LED9
LED10
LED11
LED1±
LED13
LED14
LED15
±0k
T
SET
15k
OVP
SET
I
V
C
3754 TA06
RT
SET
30.9k ±3.±k
115k
5.76k
5.1k
4.7nF
L1: COOPER BUSSMANN HC9-100-R
M1: VISHAY SILICONIX Si7ꢀ50DP
D1: DIODES, INC. PDS560
3754f
25
LT3754
TYPICAL APPLICATIONS
14W LED Driver, ꢀ00kHz Boost, 4 Strings, 80mA Per String
L1
15μH
D1
UP TO 45V OF LEDs PER STRING
1±V
IN
10V TO 14V
4.7μF
±5V
V
IN
5 s ±.±μF
100V
INTV
CC
4.7μF
10V
M1
GATE
SENSE
V
•
•
•
•
•
•
•
•
•
•
•
•
IN
0.0±Ω
LT3754
1M
100k
FAULT
V
OUT
SHDN/UVLO
GND
LED1
LED±
SYNC
LED3
LED4
LED5
PWM
CTRL
REF
PWM DIMMING
LED6
LED7
ANALOG DIMMING
LEDꢀ
LED9
LED10
LED11
LED1±
LED13
LED14
LED15
LED16
±0k
T
SET
11k
OVP
I
V
C
RT
SET
SET
3754 TA06
30.9k
±0k
60.4k
14.7k 7.5k
4.7nF
L1: SUMIDA CDRHꢀD3ꢀ
M1: VISHAY SILICONIX Si730ꢀDN
D1: DIODES, INC. DFLS160
3754f
26
LT3754
PACKAGE DESCRIPTION
DH Package
32-Lead Plastic QFN (5mm × 5mmꢁ
(Reference LTC DWG # 05-0ꢀ-1693)
0.70 p0.05
5.50 p0.05
4.10 p0.05
3.45 p 0.05
3.50 REF
(4 SIDES)
3.45 p 0.05
PACKAGE OUTLINE
0.±5 p 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 s 45° CHAMFER
R = 0.05
TYP
0.00 – 0.05
R = 0.115
TYP
0.75 p 0.05
5.00 p 0.10
(4 SIDES)
31 3±
0.40 p 0.10
PIN 1
TOP MARK
(NOTE 6)
1
±
3.45 p 0.10
3.50 REF
(4-SIDES)
3.45 p 0.10
(UH3±) QFN 0406 REV D
0.±00 REF
0.±5 p 0.05
0.50 BSC
NOTE:
1. DRAWING PROPOSED TO BE A JEDEC PACKAGE OUTLINE
M0-±±0 VARIATION WHHD-(X) (TO BE APPROVED)
±. 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.±0mm 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
3754f
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.
27
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
LT359ꢀ
LT3599
LT3595
LTC37ꢀ3
LT3517
LT351ꢀ
LT34ꢀ6
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, ±.5MHz Boost 4-Channel 100mA
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,
= 40V, 3,000:1 True Color PWM Dimming,
IN(MIN)
IN(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
IN(MAX)
IN(MIN)
OUT(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
LT347ꢀ/LT347ꢀ-1 4.5A, ±MHz High Current LED Driver with
3,000:1 Dimming
V
SD
= ±.ꢀV, 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-±ꢀ
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
= ±.ꢀV, V
= <10μA, 5mm × 7mm QFN-10
IN(MIN) IN(MAX)
I
3754f
LT 0809 • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
28
●
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© LINEAR TECHNOLOGY CORPORATION 2009
(40ꢀ) 43±-1900 FAX: (40ꢀ) 434-0507 www.linear.com
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