FeaTures
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LT3477
3A, DC/DC Converter
with Dual Rail-to-Rail
Current Sense
DescripTion
The
LT
®
3477
is a current mode, 3A DC/DC step-up converter
with dual rail-to-rail current sense amplifiers and an internal
3A, 42V switch. It combines a traditional voltage feedback
loop and two unique current feedback loops to operate
as a constant-current, constant-voltage source. Both cur-
rent sense voltages are set at 100mV and can be adjusted
independently using the I
ADJ1
and I
ADJ2
pins. Efficiency
of up to 93% can be achieved in typical applications. The
LT3477 features a programmable soft-start function to
limit inductor current during start-up. Both inputs of the
error amplifier are available externally allowing positive
and negative output voltages (boost, inverting, SEPIC,
Flyback). The switching frequency is programmable from
200kHz to 3.5MHz through an external resistor.
Available in thermally enhanced 20-pin (4mm
×
4mm)
QFN and 20-pin TSSOP packages, the LT3477 provides a
complete solution for both constant-voltage and constant-
current applications.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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Dual 100mV Rail-to-Rail Current Sense Amplifiers
Wide Input Voltage Range: 2.5V to 25V
3A, 42V Internal Switch
High Efficiency Power Conversion: Up to 93%
Drives LEDs in Boost, Buck-Boost or Buck Mode
Frequency Set by External Resistor: 200kHz to 3.5MHz
Programmable Soft-Start
Low V
CESAT
Switch: 0.3V at 2.5A
Capable of Positive and Negative Output Voltages
(Boost, Inverting, SEPIC, Flyback)
Available in Thermally Enhanced 20-Lead
(4mm
×
4mm) QFN and 20-Lead TSSOP Packages
applicaTions
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High Power LED Driver
DSL Modems
Distributed Power
Input/Output Current Limited Boost, SEPIC,
Inverting, Flyback Converters
Constant-Voltage, Constant-Current Source
Typical applicaTion
330mA LED Driver With Open LED Protection
V
IN
5V
10µH
3.3µF
200k
FBN
10k
LT3477
I
SP2
0.3
V
C
V
REF
1k
FBP
GND
SS
33nF
22k
I
SN2
R
T
330mA
3.3µF
Efficiency
90
I
SP1
V
IN
I
ADJ1
I
ADJ2
I
SN1
SW
85
80
EFFICIENCY (%)
75
70
65
60
55
50
0
0.1
0.2
I
OUT
(A)
3477 TA01b
SHDN
SHDN
0.3
0.4
4.7nF
3477 TA01a
3477fd
For more information
www.linear.com/LT3477
1
LT3477
absoluTe MaxiMuM raTings
(Note 1)
SW Pin Voltage ........................................................ 42V
V
IN
,
SHDN
Pin Voltage ............................................. 25V
FBP, FBN Pin Voltage ................................................. 6V
V
REF
Pin Voltage......................................................... 6V
R
T
, V
C
, SS Pin Voltage ............................................... 6V
I
ADJ1
, I
ADJ2
Pin Voltage ............................................ 25V
I
SP1
, I
SP2
, I
SN1
, I
SN2
Pin Voltage ...............................42V
Junction Temperature .......................................... 125°C
Operating Temperature Range (Note 2)
LT3477E ...............................................– 40°C to 85°C
LT3477I .............................................. –40°C to 125°C
Storage Temperature Range...................– 65°C to 125°C
Lead Temperature (Soldering, 10 sec)
TSSOP .............................................................. 300°C
pin conFiguraTion
TOP VIEW
V
IN
R
T
SHDN
SS
V
C
FBN
FBP
V
REF
I
ADJ2
TOP VIEW
GND
2
3
4
5
6
7
8
9
21
19 NC
18 NC
17 SW
16 SW
15 GND
14 I
SN1
13 I
SP1
12 I
SN2
11 I
SP2
NC
1
20 NC
20 19 18 17 16
NC 1
NC 2
V
IN
3
R
T
4
SHDN
5
6
7
8
9 10
21
15 I
SP1
14 I
SN2
13 I
SP2
12 I
ADJ1
11 I
ADJ2
FBN
FBP
I
ADJ1
10
FE PACKAGE
20-LEAD PLASTIC TSSOP
UF PACKAGE
20-LEAD (4mm
×
4mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 40°C/W
EXPOSED PAD (PIN 21) IS PGND (MUST BE SOLDERED TO PCB)
T
JMAX
= 125°C,
θ
JA
= 37°C/W
EXPOSED PAD (PIN 21) IS PGND (MUST BE SOLDERED TO PCB)
orDer inForMaTion
LEAD FREE FINISH
LT3477EFE#PBF
LT3477IFE#PBF
LT3477EUF#PBF
LT3477IUF#PBF
TAPE AND REEL
LT3477EFE#TRPBF
LT3477IFE#TRPBF
LT3477EUF#TRPBF
LT3477IUF#TRPBF
http://www.linear.com/product/LT3477#orderinfo
PART MARKING
PACKAGE DESCRIPTION
20-Lead Plastic TSSOP
20-Lead Plastic TSSOP
3477
3477
20-Lead (4mm
×
4mm) Plastic QFN
20-Lead (4mm
×
4mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
–40°C to 85°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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.
V
REF
SS
V
C
I
SN1
SW
SW
2
3477fd
For more information
www.linear.com/LT3477
LT3477
elecTrical characTerisTics
PARAMETER
Minimum Input Voltage
Quiescent Current
Reference Voltage
Reference Voltage Line Regulation
Maximum V
REF
Pin Current
Soft-Start Pin Current
FBP Pin Bias Current
FBN Pin Bias Current
Feedback Amplifier Offset Voltage
Feedback Amplifier Voltage Gain
Voltage Feedback Amplifier Transconductance
Feedback Amplifier Sink Current
Feedback Amplifier Source Current
Current Sense Amplifier Sense Voltage
V
FBP
= 1.25V, V
FBN
= 1.5V, V
C
= 1V
V
FBP
= 1.25V, V
FBN
= 1V, V
C
= 0.5V
Positive Rail, V
CM
= 25V, E Grade
Positive Rail, V
CM
= 25V, I Grade
Ground
R
T
= 17.2k
R
T
= 107.4k
R
T
= 2.44k
R
T
= 17.2k
(Note 3)
I
SW
= 1A (Note 3)
SW = 40V
V
SHDN
= 5V
V
SHDN
= 0V
0.3
l
l
l
The
l
indicates specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 2.5V, V
SHDN
= 2.5V.
CONDITIONS
l
MIN
TYP
2.3
0.1
5.0
MAX
2.5
1.0
7.5
1.250
1.260
0.03
100
UNITS
V
µA
mA
V
V
%/V
µA
µA
nA
nA
mV
V/V
µS
µA
µA
V
SHDN
= 0V
V
SHDN
= 2.5V, V
C
= 0.3V (Not Switching)
E Grade
I Grade
2.5V < V
IN
< 25V, V
C
= 0.3V
Out of Pin
SS = 0.5V, Out of Pin
l
l
1.216
1.210
1.235
1.235
0.01
9
25
25
100
100
6
FBP – FBN, V
C
= 1V
–2
2
500
500
10
10
97.5
97.5
88
0.9
160
2.7
87
3
100
100
100
1
200
3.5
93
4
150
0.2
30
0.1
1.5
102.5
103
112
1.15
240
4.3
5
200
5
60
1
2
mV
mV
mV
MHz
kHz
MHz
%
A
mV
µA
µA
µA
V
Switching Frequency
Maximum Switch Duty Cycle
Switch Current Limit
Switch V
CESAT
Switch Leakage Current
SHDN
Pin Current
SHDN
Pin Threshold
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:
The LT3477E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the – 40°C to 85°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. The LT3477I is guaranteed
over the full –40°C to 125°C operating junction temperature range.
Note 3:
Switch current limit and switch V
CESAT
for UF package guaranteed
by design and/or correlation to static test.
3477fd
For more information
www.linear.com/LT3477
3
LT3477
Typical perForMance characTerisTics
Switch V
CE(SAT)
0.50
0.45
0.40
0.35
V
CE(SAT)
(V)
0.30
0.25
0.20
0.15
0.10
0.05
0
0
0.5
1.5
2
1
SWITCH CURRENT (A)
2.5
3
3477 G01
Switch Current Limit
5
V
REF
1.27
1.26
1.25
4
CURRENT (A)
125°C
25°C
V
REF
(V)
3
1.24
1.23
V
IN
= 25V
V
IN
= 2.5V
–50°C
2
1
1.22
1.21
–50 –25
0
–50
–25
50
0
75
25
TEMPERATURE (°C)
100
125
3477 G02
0
25 50 75 100 125 150
TEMPERATURE (°C)
3477 G03
SHDN
Pin Turn-On Threshold
1.6
SHDN
Pin Current
50
–50°C
Quiescent Current
6
V
C
= 0.3V
QUIESCENT CURRENT (mA)
1.4
SHDN
PIN CURRENT (µA)
40
SHDN
THRESHOLD (V)
5
30
25°C
20
125°C
10
4
1.2
3
1.0
–50
–25
50
25
75
0
TEMPERATURE (°C)
100
125
0
0
5
15
10
V
SHDN
(V)
20
25
3477 G05
2
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3477 G06
3477 G04
Soft-Start Pin Current
20
2.0
Oscillator Frequency
4
R
T
= 10k
OFFSET VOLTAGE (mV)
Feedback Amplifier Offset Voltage
3
2
1
0
–1
–2
–3
VC = 1V
VC = 0.5V
15
1.6
FREQUENCY (MHz)
1.2
I
SS
(µA)
R
T
= 15k
R
T
= 20k
10
0.8
5
0.4
0
–50 –25
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3477 G07
0
25 50
75 100 125 150
TEMPERATURE (°C)
3477 G08
–4
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3477 G09
4
3477fd
For more information
www.linear.com/LT3477
LT3477
Typical perForMance characTerisTics
FBP Pin Bias Current
50
40
30
20
10
0
–10
–50 –25
“+” INDICATES THE CURRENT
FLOWS OUT OF PIN
FBN PIN BIAS CURRENT (nA)
FBN Pin Bias Current
50
40
30
20
10
0
–10
–50 –25
“+” INDICATES THE CURRENT
FLOWS OUT OF PIN
FBP PIN BIAS CURRENT (nA)
50
25
75
0
TEMPERATURE (°C)
100
125
50
25
75
0
TEMPERATURE (°C)
100
125
3477 G10
3477 G11
Current Sense Voltage
vs Temperature
104
CURRENT SENSE VOLTAGE (mV)
Current Sense Voltage vs I
ADJ
120
100
VOLTAGE SENSE (mV)
V
CM
= 10V
103
102
101
100
99
98
97
96
–50 –25
0
75
50
25
TEMPERATURE (°C)
100
125
V
CM
= 42V
V
CM
= 10V
80
60
40
20
0
0
100 200 300 400 500 600 700 800
I
ADJ
VOLTAGE (mV)
2477 G13
3477 G14
3477fd
For more information
www.linear.com/LT3477
5
