FEATURES
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LT3797
Triple Output LED Driver
Controller
DESCRIPTION
The
LT
®
3797
is a triple output DC/DC controller designed
to drive three strings of LEDs. The fixed frequency, current
mode architecture results in stable operation over a wide
range of supply and output voltages. The LT3797 includes
an integrated DC/DC converter to produce a regulated 7.5V
supply for the N-channel MOSFET gate drivers of the three
channels. This high efficiency converter enables the part to
operate from a wide input voltage range from 2.5V to 40V.
The LT3797 is designed so that each converter can use
the most suitable configuration to drive its LED load,
whether step-up, step-down or a combination. Two key
features enable this flexibility: first the LT3797 can sense
output current at the high side of the LED string; and
second, the voltage feedback pin, FBH, is referred to the
ISP current sensing input. The CTRL inputs provide out-
put current analog dimming capability. The TG drivers
level shift the PWM signals to drive the gates of external
LED-disconnect P-channel MOSFETs, allowing high PWM
dimming range, and providing LED overcurrent protection
and short-circuit protected boost capability.
All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S. Patents, including 7199560, 7321203, 7746300.
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APPLICATIONS
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Three Independent LED Driver Channels
Wide Input Voltage Range: 2.5V to 40V
V
IN
Transient Ride-Through Up to 60V
Rail-to-Rail LED Current Sense: 0V to 100V
3000:1 PWM Dimming
TG Drivers for PMOS LED Disconnection
Operates in Boost, Buck Mode, Buck-Boost Mode,
SEPIC or Flyback Topology
Open-LED Protection
Short-Circuit Protected Boost Capable
Fault Flags for Independent Channels
Programmable V
IN
Undervoltage and Overvoltage
Lockout
Adjustable Switching Frequency: 100kHz to 1MHz
Synchronizeable to an External Clock
CTRL Pins Provide Analog Dimming
Programmable Soft-Start
Low Profile 52-Lead 7mm x 8mm QFN and 48-Lead
Exposed Pad LQFP
Automotive and Industrial Lighting
RGB Lighting
Billboards and Large Displays
TYPICAL APPLICATION
V
IN
2.5V TO 40V
(60V TRANSIENT,
41V INTERNAL
OVLO PROTECTION)
4.7µF
×3
10µH
Triple Boost LED Driver
10µH
ISP1
250m
ISN1
4.7µF
100V
×3
ISP2
250m
ISN2
4.7µF
100V
×3
10µH
ISP3
250m
ISN3
4.7µF
100V
×3
8m
1A
50V
8m
1A
50V
8m
1A
50V
GATE1 SENSEP1 SENSEN1 TG1
V
IN
1µF
100k
EN/UVLO
105k
OVLO V
REF
CTRL1-3 PWM1-3
V
IN
GATE2 SENSEP2 SENSEN2 TG2
LT3797
GATE3 SENSEP3 SENSEN3 TG3
ISN1-3
ISP1-3
23.2k
FBH1-3
RT
SYNC SS1-3
47.5k
310kHz
FLT1-3
SW1 SW2 BOOST
0.1µF
47µH
INTV
CC
GND
VC1-3
3.9k
6.8nF
3797 TA01
1M
140k
10µF
0.1µF
1M
Rev C
Document Feedback
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1
LT3797
ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
IN
, EN/UVLO............................................................60V
INTV
CC
, SYNC, OVLO, PWM1, PWM2, PWM3 ............8V
ISN1 .......................................................ISP1-1.5V, 100V
ISN2 .......................................................ISP2-1.5V, 100V
ISN3 .......................................................ISP3-1.5V, 100V
FBH1 ...................................................... ISP1 ±6V, 100V
FBH2 ...................................................... ISP2 ±6V, 100V
FBH3 ...................................................... ISP3 ±6V, 100V
VC1, VC2, VC3, V
REF
, SS1, SS2, SS3 ..........................3V
CTRL1, CTRL2, CTRL3,
FLT1, FLT2, FLT3...................12V
RT ............................................................................1.5V
SENSEP1, SENSEP2, SENSEP3, SENSEN1,
SENSEN2, SENSEN3, .............................................±0.3V
SW1, SW2, BOOST, TG1, TG2, TG3, GATE1,
GATE2, GATE3 .................................................. (Note 2)
Operating Ambient Temperature Range
(Note 3) ...................................................... –40 to 125°C
Maximum Junction Temperature .......................... 125°C
Storage Temperature Range .................. –65°C to 150°C
PIN CONFIGURATION
TOP VIEW
SENSEN3
SENSEP3
EN/UVLO
INTV
CC
INTV
CC
BOOST
GATE3
OVLO
SW1
SW2
SS3
TOP VIEW
V
IN
52 51 50 49 48 47 46 45 44 43 42 41
FLT1
1
FLT2
2
FLT3
3
PWM1 4
PWM2 5
PWM3 6
V
REF
7
CTRL1 8
CTRL2 9
CTRL3 10
RT 11
SYNC 12
28 VC2
15 16 17
ISN1
ISP1
FBH1
19 20 21 22 23 24 25 26
VC1
SS1
SENSEN1
SENSEP1
GATE2
GATE1
SENSEP2
SENSEN2
TG1 14
27 SS2
53
GND
38 FBH3
37 ISP3
36 ISN3
35 TG3
33 TG2
32 ISN2
31 ISP2
30 FBH2
FLT1
1
FLT2
2
FLT3
3
PWM1 4
PWM2 5
PWM3 6
V
REF
7
CTRL1 8
CTRL2 9
CTRL3 10
RT 11
SYNC 12
40 VC3
48
47
46
45
44
43
42
41
40
39
38
37
OVLO
ENUVLO
V
IN
SW1
BOOST
SW2
INTV
CC
INTV
CC
GATE3
SENSEP3
SENSEN3
SS3
49
GND
36
35
34
33
32
31
30
29
28
27
26
25
VC3
FBH3
ISP3
ISN3
TG3
NC
TG2
ISN2
ISP2
FBH2
VC2
SS2
UKG PACKAGE
VARIATION: UKG52(47)
52-LEAD (7mm
×
8mm) PLASTIC QFN
θ
JA
= 28°C/W
EXPOSED PAD (PIN 53) IS GND, MUST BE SOLDERED TO PCB
LXE PACKAGE
48-LEAD (7mm
×
7mm) PLASTIC LQFP
θ
JA
= 19°C/W
EXPOSED PAD (PIN 49) IS GND, MUST BE SOLDERED TO PCB
TG1 13
ISN1 14
ISP1 15
FBH1 16
VC1 17
SS1 18
SENSEN1 19
SENSEP1 20
GATE1 21
GATE2 22
SENSEP2 23
SENSEN2 24
Rev C
2
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LT3797
ORDER INFORMATION
LEAD FREE FINISH
LT3797EUKG#PBF
LT3797IUKG#PBF
LT3797ELXE#PBF
LT3797ILXE#PBF
TAPE AND REEL
(QFN)/TRAY (LXE)
LT3797EUKG#TRPBF
LT3797IUKG#TRPBF
LT3797ELXE#PBF
LT3797ILXE#PBF
http://www.linear.com/product/LT3797#orderinfo
PACKAGE DESCRIPTION
52-Lead (7mm
×
8mm) Plastic QFN
52-Lead (7mm
×
7mm) Plastic QFN
48-Lead (7mm
×
7mm) Plastic eLQFP
48-Lead (7mm
×
7mm) Plastic eLQFP
MSL RATING
1
1
3
3
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
PART
MARKING*
LT3797UKG
LT3797UKG
LT3797LXE
LT3797LXE
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
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/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
ELECTRICAL CHARACTERISTICS
PARAMETER
V
IN
Minimum Operation Voltage
V
IN
Overvoltage Lockout
V
IN
Shutdown I
Q
V
IN
Operating I
Q
(Not Switching)
INTV
CC
Operating I
Q
(Not Switching)
V
REF
Voltage
V
REF
Line Regulation
SENSEP1-SENSEN1, SENSEP2-SENSEN2,
SENSEP2-SENSEN2 Current Limit Threshold
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 24V; EN/UVLO = 24V; CTRL1, CTRL2, CTRL3, PWM1, PWM2,
PWM3 = 2V; SENSEN1, SENSEN2, SENSEN3 = 0V, OVLO = 0V, unless otherwise noted.
CONDITIONS
l
MIN
l
TYP
41
1
0.1
0.5
2.4
MAX
2.5
42.5
1
15
0.75
3
2.04
120
UNITS
V
V
V
µA
µA
mA
mA
V
%/V
mV
μA
μA
Rising V
IN
Falling Hysteresis
EN/UVLO = 0V
EN/UVLO = 1.15V
PWM1, PWM2, PWM3 = 0V, INTV
CC
= 8V
PWM1, PWM2, PWM3 = 0V, INTV
CC
= 8V
0µA ≤ I
VREF
≤ 450µA, INTV
CC
= 8V
2.5V ≤ V
IN
≤ 40V, INTV
CC
= 8V
40
l
1.955
100
2.00
0.001
110
55
210
l
SENSEP1, SENSEP2, SENSEP3 Input Bias Current Current Out of Pin, SENSEP1, SENSEP2,
SENSEP3 = 0V
SENSEN1, SENSEN2, SENSEN3 Input Bias Current Current Out of Pin
Integrated INTV
CC
Power Supply (Note 7)
INTV
CC
Regulation Voltage
INTV
CC
Undervoltage Lockout Threshold
INTV
CC
Line Regulation (ΔV
INTVCC
/ΔV
IN
)
Error Amplifiers
LED Current Sense Threshold (ISP1-ISN1,
ISP2-ISN2, ISP3-ISN3)
8/10th LED Current Sense Threshold (ISP1-ISN1,
ISP2-ISN2, ISP3-ISN3)
1/10th LED Current Sense Threshold (ISP1-ISN1,
ISP2-ISN2, ISP3-ISN3)
CTRL1, CTRL2, CTRL3 Range for Linear Current
Sense Threshold Adjustment
CTRL1, CTRL2, CTRL3 Input Bias Current
CTRL1, CTRL2, CTRL3 Idle Mode Threshold
Current Out of Pin, CTRL1, CTRL2, CTRL3 = 0.3V
Falling
Hysteresis
135
ISP1, ISP2, ISP3, FBH1, FBH2, FBH3 = 48V
ISN1, ISN2, ISN3, FBH1, FBH2, FBH3 = 0V
CTRL1, CTRL2, CTRL3=1.1V, ISP1, ISP2, ISP3 = 48V
CTRL1, CTRL2, CTRL3=1.1V, ISN1, ISN2, ISN3 = 0V
CTRL1, CTRL2, CTRL3=0.3V, ISP1, ISP2, ISP3 = 48V
CTRL1, CTRL2, CTRL3=0.3V, ISN1, ISN2, ISN3 = 0V
l
l
l
l
l
l
l
l
7.15
5.15
7.5
5.25
0.4
0.001
7.75
5.4
0.02
257
272
203.5
218
29
34
1.2
V
V
V
%
mV
mV
mV
mV
mV
mV
V
nA
mV
mV
Rev C
Falling INTV
CC
Hysteresis
2.5V < V
IN
< 40V
243
238
194.5
192
17
15
0.2
250
250
200
200
25
25
50
150
20
100
170
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3
LT3797
ELECTRICAL CHARACTERISTICS
PARAMETER
LED Current Sense Amplifier Input Common Mode
Range (ISN1, ISN2, ISN3)
LED Overcurrent Protection Threshold
(ISP1-ISN1, ISP2-ISN2, ISP3-ISN3)
ISP1, ISP2, ISP3 Input Bias Current (Active)
ISP1, ISP2, ISP3 Input Bias Current (Idle)
ISP1, ISP2, ISP3, FBH1, FBH2, FBH3 = 12V
ISP1, ISP2, ISP3, ISN1, ISN2, ISN3 = 48V
ISP1, ISP2, ISP3, ISN1, ISN2, ISN3 = 0V
PWM1, PWM2, PWM3=0V , ISP1, ISP2, ISP3, ISN1,
ISN2, ISN3 = 48V
PWM1, PWM2, PWM3, ISP1, ISP2, ISP3, ISN1, ISN2,
ISN3 = 0V
ISN1, ISN2, ISN3 Input Bias Current (Active)
ISN1, ISN2, ISN3 Input Bias Current (Idle)
ISP1, ISP2, ISP3, ISN1, ISN2, ISN3 = 48V
ISP1, ISP2, ISP3, ISN1, ISN2, ISN3 = 0V
PWM1, PWM2, PWM3=0V , ISP1, ISP2, ISP3, ISN1,
ISN2, ISN3 = 48V
PWM1, PWM2, PWM3, ISP1, ISP2, ISP3, ISN1, ISN2,
ISN3 = 0V
LED Current Sense Amplifier g
m
ISP1-ISN1, ISP2-ISN2, ISP3-ISN3 = 250mV
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 24V; EN/UVLO = 24V; CTRL1, CTRL2, CTRL3, PWM1, PWM2,
PWM3 = 2V; SENSEN1, SENSEN2, SENSEN3 = 0V, OVLO = 0V, unless otherwise noted.
CONDITIONS
l
MIN
0
TYP
MAX
100
UNITS
V
mV
µA
nA
µA
nA
µA
nA
1000
630
–100
2
–40
20
–100
0
–20
250
1.225
1.250
40
2.4
480
FBH(REG) FBH(REG) FBH(REG)
– 0.07
– 0.05
– 0.04
20
FBH(REG) FBH(REG) FBH(REG)
+ 0.05
+ 0.06
+ 0.085
25
10
–20
–20
4
10.5
12
32
20
20
1.280
100
3
1
µA
nA
μS
V
nA
µA
μS
V
mV
V
mV
MΩ
nA
nA
V/V
µA
µA
µA
FBH1, FBH2, FBH3 Regulation Voltage “FBH(REG)” ISP1, ISP2, ISP3, ISN1, ISN2, ISN3 = 48V
(|ISP1-FBH1, ISP2-FBH2, ISP3-FBH3|)
FBH1, FBH2, FBH3 Pin Input Bias Current
FBH1, FBH2, FBH3 Amplifier g
m
FBH1, FBH2, FBH3 Open-LED Threshold
(|ISP1-FBH1|, |ISP2-FBH2|, |ISP3-FBH3|) Voltage
FBH1, FBH2, FBH3 Overvoltage Threshold
(|ISP1-FBH1|, |ISP2-FBH2|, |ISP3-FBH3|) Voltage
VC1, VC2, VC3 Output Impedance
VC1, VC2, VC3 Standby Input Bias Current
VC1, VC2, VC3 Current Mode Gain –ΔV
VC
/ΔV
SENSE
VC1, VC2, VC3 Source Current
VC1, VC2, VC3 Sink Current
ISP1, ISP2, ISP3, ISN1, ISN2, ISN3, FBH1, FBH2,
FBH3 = 48V, Current Out of Pin
ISP1, ISP2, ISP3, FBH1, FBH2, FBH3 = 48V,
ISN1, ISN2, ISN3 = 47.7V
ISP1, ISP2, ISP3, ISN1, ISN2, ISN3 = 48V,
FBH1, FBH2, FBH3 = 46.7V
Oscillator
Switching Frequency
R
T
= 154kΩ
R
T
= 35.7kΩ
R
T
= 12.4kΩ
C
GATE
= 3300pF
C
GATE
= 3300pF
PWM1, PWM2, PWM3 = 0V
CTRL1, CTRL2, CTRL3 = 0V
ISP1-FBH1, ISP2-FBH2, ISP3-FBH3 = 1.25V
ISP1-FBH1, ISP2-FBH2, ISP3-FBH3 = –1.25V
|ISP1-FBH1|, |ISP2-FBH2|, |ISP3-FBH3| = 1.25V
Rising (Note 4)
ISP1, ISP2, ISP3, ISN1, ISN2, ISN3 = 48V
Hysteresis
Rising (Note 4)
ISP1, ISP2, ISP3, ISN1, ISN2, ISN3 = 48V
Hysteresis
2
l
95
375
950
100
400
1000
1.05
200
220
107
425
1050
270
300
0.4
kHz
kHz
kHz
V
ns
ns
V
Rev C
RT Voltage
GATE1, GATE2, GATE3 Minimum Off-Time
GATE1, GATE2, GATE3 Minimum On-Time
SYNC Input Low
l
4
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LT3797
ELECTRICAL CHARACTERISTICS
PARAMETER
SYNC Input High
SYNC Resistance to GND
Logic Inputs/Outputs
EN/UVLO Threshold Voltage Falling
EN/UVLO Rising Hysteresis
EN/UVLO Input Low Voltage
EN/UVLO Pin Bias Current Low
EN/UVLO Pin Bias Current High
OVLO Pin Input Bias Current
OVLO Threshold Voltage
PWM1, PWM2, PWM3 Input High Voltage
PWM1, PWM2, PWM3 Input Low Voltage
PWM1, PWM2, PWM3 Resistance to GND
FLT1, FLT2, FLT3
Output Low
SS1, SS2, SS3 Sourcing Current
SS1, SS2, SS3 Sinking Current
SS1, SS2, SS3 Soft-Start Reset Threshold
SS1, SS2, SS3 Fault Reset Threshold
NMOS Gate Drivers
GATE1, GATE2, GATE3 Output Rise Time (t
r
)
GATE1, GATE2, GATE3 Output Fall Time (t
f
)
Gate Output Low (V
OL
)
Gate Output High (V
OH
)
PMOS Gate Drivers
TG1, TG2, TG3 Turn-On Time
TG1, TG2, TG3 Turn-Off Time
PMOS Gate On Voltage
(ISP1-TG1, ISP2-TG2, ISP3-TG3)
PMOS Gate Off Voltage
(ISP1-TG1, ISP2-TG2, ISP3-TG3)
C
TG
= 1000pF, ISP1, ISP2, ISP3, FBH1, FBH2,
FBH3 = 48V (Note 6)
C
TG
= 1000pF, ISP1, ISP2, ISP3, FBH1, FBH2,
FBH3 = 48V (Note 6)
ISP1, ISP2, ISP3, FBH1, FBH2, FBH3 = 48V
ISP1, ISP2, ISP3, FBH1, FBH2, FBH3 = 48V
200
70
6.5
0.3
ns
ns
V
V
INTV
CC
– 0.05
C
GATE
= 3300pF (Note 5)
C
GATE
= 3300pF (Note 5)
25
25
0.1
ns
ns
V
V
I
FLT
=1mA
SS1, SS2, SS3 = 1V, Current Out of Pin
SS1, SS2, SS3 = 1V, OVLO =1.3V
Falling, Measured on SS1, SS2, SS3
Hysteresis
Measured on SS1, SS2, SS3
28
2.8
160
30
1.7
Rising
Hysteresis
l
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 24V; EN/UVLO = 24V; CTRL1, CTRL2, CTRL3, PWM1, PWM2,
PWM3 = 2V; SENSEN1, SENSEN2, SENSEN3 = 0V, OVLO = 0V, unless otherwise noted.
CONDITIONS
l
MIN
1.5
TYP
200
MAX
UNITS
V
kΩ
1.180
1.220
20
1.255
0.4
V
mV
V
µA
nA
nA
V
mV
V
V
kΩ
I
VIN
Drops Below 1µA
EN/UVLO = 1.15V
EN/UVLO = 1.33V
1.225
l
1.5
2
40
20
1.250
125
1.1
0.9
200
2.6
100
100
1.280
1.4
0.6
300
mV
µA
µA
mV
mV
V
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
Do not apply a positive or negative voltage or current source
to SW1, SW2, GATE1, GATE2, GATE3, TG1, TG2, TG3 pins, otherwise
permanent damage may occur.
Note 3:
The LT3797E is guaranteed to meet performance specifications
from the 0°C to 125°C junction temperature. Specifications over the
–40°C to 125°C operating junction temperature range are assured by
design, characterization and correlation with statistical process controls.
The LT3797I is guaranteed over the full –40°C to 125°C operating junction
temperature range.
Note 4:
FBH(REG) denotes the regulation voltage (|ISP-FBH|) of the
corresponding FBH pin.
Note 5:
Rise and fall times are measured at 10% and 90% levels.
Note 6:
Gate turn-on/turn-off time is measured from 50% level of PWM
voltage to 90% level of gate on/off voltage.
Note 7:
The INTV
CC
regulation voltage is tested in an open loop. Closed
loop operation is guaranteed by design and process controls.
Rev C
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5
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