LT3955
60V
IN
LED Converter with
Internal PWM Generator
FeaTures
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DescripTion
The
LT
®
3955
is a DC/DC converter designed to operate as
a constant-current source and constant-voltage regula-
tor. It features an internal low side N-channel MOSFET
rated for 80V/3.5A. The LT3955 is ideally suited for driv-
ing high current LEDs, but also has features to make it
suitable for charging batteries and supercapacitors. The
fixed frequency, current mode architecture results in
stable operation over a wide range of supply and output
voltages. A voltage feedback pin serves as the input for
several LED protection features, and also makes it possible
for the converter to operate as a constant-voltage source.
A frequency adjust pin allows the user to program the
frequency from 100kHz to 1MHz to optimize efficiency,
performance or external component size.
The LT3955 senses output current at the high side or at
the low side of the load. The PWM input can be configured
to self-oscillate at fixed frequency with duty ratio pro-
grammable from 4% to 96%. When driven by an external
signal, the PWM input provides LED dimming ratios of
up to 3000:1. The CTRL input provides additional analog
dimming capability.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Protected by U.S. Patents including 7199560, 7321203.
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3000:1 True Color PWM™ Dimming for LEDs
Wide V
IN
Range: 4.5V to 60V
Rail-to-Rail Current Sense Range: 0V to 80V
Internal 80V/3.5A Switch
Programmable PWM Dimming Signal Generator
Constant Current (±3%) and Constant-Voltage
(±2%) Regulation
Accurate Analog Dimming
Drives LEDs in Boost, SEPIC, CUK, Buck Mode,
Buck-Boost Mode, or Flyback Configuration
Output Short-Circuit Protected Boost
Open LED Protection and Reporting
Adjustable Switching Frequency: 100kHz to 1MHz
Programmable V
IN
UVLO with Hysteresis
C/10 Indication for Battery Chargers
Low Shutdown Current: <1µA
Thermally Enhanced 5mm
×
6mm QFN Package
applicaTions
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High Power LEDs
Output Short-Circuit Protected Boost
Battery and SuperCap Chargers
Accurate Current Limited Voltage Regulators
Typical applicaTion
94% Efficiency 20W Boost LED Driver with Internal PWM Dimming
V
IN
5V TO 60V
22µH
4.7µF
×2
499k
147k
1M
165k
INTV
CC
100k
DIM
124k
V
IN
EN/UVLO
V
REF
LT3955
CTRL
ISN
1M
VMODE
DIM/SS
SYNC
PWM
RT
PWMOUT
V
C
GND GNDK INTV
CC
INTV
CC
1µF
3955 TA01a
SW
PGND
ISP
2.2µF
×5
PWM Dimming Waveforms at
Various DIM Voltage Settings
V
DIM
= 8V
DC
PWM
= 97.2%
0.82
300mA
I
LED
0.3A/DIV
V
DIM
= 3.87V
DC
PWM
= 50%
V
DIM
= 1.47V
DC
PWM
= 10%
V
DIM
= 0V
DC
PWM
= 2.8%
FB
16.9k
20W LED STRING
(CURRENT DERATED
FOR V
IN
< 9V)
V
IN
= 24V
V
LED
= 65V
0.5ms/DIV
3955 TA01b
10nF
28.7k
350kHz
5.1k
47nF
300Hz 4.7nF
NOTE: GND, GNDK AND SIGNAL LEVEL COMPONENTS MUST BE CONNECTED EXTERNALLY AS SHOWN.
AN INTERNAL CONNECTION BETWEEN GNDK AND PGND PINS PROVIDES GROUNDING TO THE SUPPLY.
3955fb
For more information
www.linear.com/LT3955
1
LT3955
absoluTe maximum raTings
V
IN
, EN/UVLO............................................................60V
ISP, ISN, SW .............................................................80V
INTV
CC
...................................................V
IN
+ 0.3V, 9.6V
PWMOUT ........................................................... (Note 2)
CTRL,
VMODE
...........................................................15V
FB, PWM, SYNC.......................................................9.6V
V
C
, V
REF
......................................................................3V
RT, DIM/SS ..............................................................1.5V
PGND, GNDK to GND .............................................±0.5V
Operating Ambient Temperature Range
(Notes 3, 4) ............................................ –40°C to 125°C
Maximum Junction Temperature .......................... 125°C
Storage Temperature Range .................. –65°C to 150°C
(Note 1)
pin conFiguraTion
TOP VIEW
DIM/SS
VMODE
CTRL
PWM
V
REF
RT
36 35 34 33 32 31 30
SYNC 1
EN/UVLO 2
INTV
CC
3
GND 4
V
IN
6
SW 8
SW 9
NC 10
12 13 14 15 16 17
PGND
PGND
PGND
PGND
PGND
GNDK
38
SW
37
GND
28 ISP
27 ISN
25 FB
24 GND
23 PWMOUT
21 SW
20 SW
UHE PACKAGE
36-LEAD (5mm
×
6mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W,
θ
JC
= 3°C/W
EXPOSED PAD (PIN 37) IS GND, MUST BE SOLDERED TO GND PLANE
EXPOSED PAD (PIN 38) IS SW, MUST BE SOLDERED TO SW PLANE
orDer inFormaTion
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3955EUHE#PBF
LT3955EUHE#TRPBF
3955
36-Lead (5mm
×
6mm) Plastic QFN
–40°C to 125°C
LT3955IUHE#PBF
LT3955IUHE#TRPBF
3955
36-Lead (5mm
×
6mm) Plastic QFN
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
V
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3955fb
For more information
www.linear.com/LT3955
LT3955
elecTrical characTerisTics
PARAMETER
V
IN
Minimum Operating Voltage
V
IN
Shutdown I
Q
V
IN
Operating I
Q
(Not Switching)
V
REF
Voltage
V
REF
Line Regulation
V
REF
Pull-Up Current
SW Pin Current Limit
SW Pin Leakage
SW Pin Voltage Drop
DIM/SS Pull-Up Current
DIM/SS Voltage Clamp
Error Amplifier
Full-Scale ISP/ISN Current Sense Threshold
(V
ISP–ISN
)
1/10th Scale ISP/ISN Current Sense Threshold
(V
ISP–ISN
)
Mid-Scale ISP/ISN Current Sense Threshold
(V
ISP–ISN
)
ISP/ISN Overcurrent Threshold
ISP/ISN Current Sense Amplifier Input Common Mode
Range (V
ISN
)
ISP/ISN Input Bias Current High Side Sensing (Combined) PWM = 5V (Active), ISP = ISN = 48V
PWM = 0V (Standby), ISP = ISN = 48V
ISP/ISN Input Bias Current Low Side Sensing (Combined) PWM = 5V, ISP = ISN = 0V
ISP/ISN Current Sense Amplifier g
m
(High Side Sensing)
ISP/ISN Current Sense Amplifier g
m
(Low Side Sensing)
CTRL Pin Range for Linear Current Sense Threshold
Adjustment
CTRL Input Bias Current
V
C
Output Impedance
V
C
Standby Input Bias Current
FB Regulation Voltage (V
FB
)
FB Amplifier g
m
FB Pin Input Bias Current
FB Open LED Threshold
C/10 Inhibit for
VMODE
Assertion (V
ISP–ISN
)
FB Overvoltage Threshold
Oscillator
Switching Frequency
SW Minimum Off-Time
SW Minimum On-Time
SYNC Input Low
R
T
= 95.3kΩ
R
T
= 8.87kΩ
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, CTRL = 2V, PWM = 5V, unless otherwise noted.
CONDITIONS
V
IN
Tied to INTV
CC
EN/UVLO = 0V, PWM = 0V
EN/UVLO = 1.15V, PWM = 0V
PWM = 0V
–100µA ≤ I
VREF
≤ 0µA
4.5V ≤ V
IN
≤ 60V
V
REF
= 0V
SW = 48V
I
SW
= 2A
Current Out of Pin, DIM/SS = 0V
I
DIM/SS
= 0µA
CTRL ≥ 1.2V, ISP = 48V, 0V ≤ FB ≤ 1.18V
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CTRL ≥ 1.2V, ISN = 0V, 0V ≤ FB ≤ 1.18V
l
CTRL = 0.2V, ISP = 48V, 0V ≤ FB ≤ 1.18V
l
CTRL = 0.2V, ISN = 0V, 0V ≤ FB ≤ 1.18V
l
CTRL = 0.5V, ISP = 48V, 0V ≤ FB ≤ 1.18V
l
CTRL = 0.5V, ISN = 0V, 0V ≤ FB ≤ 1.18V
l
242
243
21
20
96
94
0
100
0.1
–230
120
70
l
l
l
l
l
l
MIN
TYP
0.1
1.7
MAX
4.5
1
6
2.2
2.06
210
4.9
10
14
UNITS
V
µA
µA
mA
V
%/V
µA
A
µA
mV
µA
V
1.965
150
3.5
2.02
0.001
185
4.2
5
200
10
12
1.2
250
257
25
28
100
105
600
258
268
30
36
104
115
80
mV
mV
mV
mV
mV
mV
mV
V
µA
µA
µA
µS
µS
V
ISP–ISN
= 250mV, ISP = 48V
V
ISP–ISN
= 250mV, ISN = 0V
0
1.0
50
15
100
20
1.255
500
40
100
39
1.275
V
nA
MΩ
nA
V
µS
nA
V
mV
V
kHz
kHz
ns
ns
Current Out of Pin
0.9V ≤ V
C
≤ 1.5V
PWM = 0V
ISP = ISN = 48V, 0V
FB = V
FB
, ISP = ISN = 48V
Current Out of Pin, FB = V
FB
VMODE
Falling, ISP Tied to ISN
FB = V
FB
, ISN = 48V, 0V
PWMOUT Falling
14
l
–20
1.225
l
V
FB
– 65mV V
FB
– 50mV V
FB
– 40mV
25
V
FB
+ 50mV V
FB
+ 60mV V
FB
+ 70mV
85
925
100
1000
160
180
0.4
115
1050
V
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For more information
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LT3955
elecTrical characTerisTics
PARAMETER
SYNC Input High
Linear Regulator
INTV
CC
Regulation Voltage
INTV
CC
Maximum Operating Voltage
INTV
CC
Minimum Operating Voltage
Dropout (V
IN
– INTV
CC
)
INTV
CC
Undervoltage Lockout
INTV
CC
Current Limit
INTV
CC
Current in Shutdown
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
VMODE
Output Low
VMODE
Pin Leakage
PWM Pin Signal Generator
PWM Falling Threshold
PWM Threshold Hysteresis (V
PWMHYS
)
PWM Pull-Up Current (I
PWMUP
)
PWM Pull-Down Current (I
PWMDN
)
PWM Fault-Mode Pull-Down Current
PWMOUT Duty Ratio for PWM Signal Generator (Note 5)
I
DIM/SS
= 0µA
PWM = 0.7V, I
DIM/SS
= 0µA
PWM = 1.5V, I
DIM/SS
= 0µA
INTV
CC
= 3.6V
I
DIM/SS
= –6.5µA
I
DIM/SS
= 0µA
I
DIM/SS
= 21.5µA
I
DIM/SS
= 52µA
PWM = 47nF to GND, I
DIM/SS
= 0µA
C
L
= 560pF
C
L
= 560pF
PWM = 0V
INTV
CC
– 0.05
3.1
6.2
40
95
170
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The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 24V, EN/UVLO = 24V, CTRL = 2V, PWM = 5V, unless otherwise noted.
CONDITIONS
MIN
1.5
10V ≤ V
IN
≤ 60V
l
TYP
MAX
UNITS
V
7.60
8.1
7.85
8.05
4.5
V
V
V
mV
V
mA
µA
V
mV
V
µA
nA
mV
µA
V
V
µA
µA
mA
%
%
%
%
Hz
ns
ns
I
INTVCC
= –10mA, V
IN
= 7V
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390
3.9
30
4.1
36
8
1.180
1.220
40
4.4
42
13
1.260
0.4
1.7
2.2
10
0.1
0.78
0.35
6
68
0.83
0.47
7.5
88
1.5
4.1
7.9
48
96.5
300
35
35
0.05
5.2
9.2
56
98
390
2.7
100
200
5
0.88
0.6
9
110
8V ≤ V
IN
≤ 60V, INTV
CC
= 6V
EN/UVLO = 0V, INTV
CC
= 8V
I
VIN
Drops Below 1µA
EN/UVLO = 1.15V
EN/UVLO = 1.33V
I
VMODE
= 1mA
FB = 0V,
VMODE
= 12V
PWMOUT Signal Generator Frequency
PWMOUT Driver
PWMOUT Driver Output Rise Time (t
r
)
PWMOUT Driver Output Fall Time (t
f
)
PWMOUT Output Low (V
OL
)
PWMOUT Output High (V
OH
)
V
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
PWMOUT pin, otherwise permanent damage may occur.
Note 3:
The LT3955E 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
LT3955I is guaranteed over the full –40°C to 125°C operating junction
temperature range.
Note 4:
The LT3955 includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed the maximum operating junction temperature
when overtemperature protection is active. Continuous operation above
the specified maximum junction temperature may impair device reliability.
Note 5:
PWMOUT Duty Ratio is calculated:
Duty = I
PWMUP
/(I
PWMUP
+ I
PWMDN
)
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For more information
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LT3955
Typical perFormance characTerisTics
V
(ISP–ISN)
Threshold
vs CTRL Voltage
300
250
V
(ISP – ISN)
THRESHOLD (mV)
V
(ISP –ISN)
THRESHOLD (mV)
200
150
100
50
0
–50
0
0.5
1
1.5
CTRL VOLTAGE (V)
2
3955 G01
T
A
= 25°C, unless otherwise noted.
V
(ISP–ISN)
Threshold
vs Temperature
265
260
ISN = 0V
255
CTRL = 2V
V
(ISP–ISN)
Threshold
vs ISP Voltage
260
CTRL = 2V
V
(ISP –ISN)
THRESHOLD (mV)
255
250
250
ISP = 48V
245
245
240
–50
240
0
20
40
60
ISP VOLTAGE (V)
80
3955 G02
–25
0
25
50
75
TEMPERATURE (°C)
100
125
3955 G03
FB Regulation Voltage (V
FB
)
vs Temperature
1.270
1.265
1.260
V
FB
(V)
1.255
1.250
1.245
1.240
–50
260
230
V
(ISP – ISN)
THRESHOLD (mV)
200
170
140
110
80
50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
3955 G04
V
(ISP–ISN)
Threshold
vs FB Voltage
200
CTRL = 2V
190
V
REF
Source Current vs
Temperature
V
REF
SOURCE CURRENT (µA)
1.245
1.25
3955 G05
180
170
160
CTRL = 0.5V
20
1.22 1.225
1.23 1.235 1.24
FB VOLTAGE (V)
150
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
3955 G06
V
REF
Voltage vs Temperature
2.05
2.04
2.03
V
REF
(V)
2.02
2.01
2.00
1.99
–50
1000
900
SWITCHING FREQUENCY (kHz)
800
700
600
500
400
300
200
–25
0
25
50
75
TEMPERATURE (°C)
100
125
3955 G07
Switching Frequency vs R
T
420
415
SWITCHING FREQUENCY (kHz)
410
405
400
395
390
385
10
R
T
(k )
100
3955 G08
Switching Frequency
vs Temperature
R
T
= 25.5k
100
380
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
3955 G09
3955fb
For more information
www.linear.com/LT3955
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