Maximum Junction Temperature (Note 2)............. 125°C
Operating Temperature Range (Note 3)
LT3475E/LT3475E-1 ............................. –40°C to 85°C
LT3475I/LT3475I-1 ............................. –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature Range (Soldering, 10 sec) ....... 300°C
ORDER INFORMATION
LEAD FREE FINISH
LT3475EFE#PBF
LT3475IFE#PBF
LT3475EFE-1#PBF
LT3475IFE-1#PBF
TAPE AND REEL
LT3475EFE#TRPBF
LT3475IFE#TRPBF
LT3475EFE-1#TRPBF
LT3475IFE-1#TRPBF
PART MARKING*
LT3475EFE
LT3475IFE
LT3475FE-1
LT3475FE-1
PACKAGE DESCRIPTION
20-Lead Plastic TSSOP
20-Lead Plastic TSSOP
20-Lead Plastic TSSOP
20-Lead Plastic TSSOP
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. *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/
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V, V
BOOST
= 16V, V
OUT
= 4V unless otherwise noted (Note 3)
PARAMETER
Minimum Input Voltage
Input Quiescent Current
Shutdown Current
Not Switching
SHDN = 0.3V, V
BOOST
= V
OUT
= 0V
CONDITIONS
●
ELECTRICAL CHARACTERISTICS
2
U
W W
W
PIN CONFIGURATION
OUT1
LED1
BOOST1
SW1
V
IN
V
IN
SW2
BOOST2
LED2
1
2
3
4
5
6
7
8
9
21
20 PWM1
19 V
ADJ1
18 V
C1
17 REF
16 SHDN
15 GND
14 R
T
13 V
C2
12 V
ADJ2
11 PWM2
OUT2 10
FE PACKAGE
20-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 30°C/W,
θ
JC
= 8°C/W
EXPOSED PAD (PIN 21) IS GROUND AND MUST
BE ELECTRICALLY CONNECTED TO THE PCB.
MIN
TYP
3.7
6
0.01
MAX
4
8
2
UNITS
V
mA
μA
3475fb
LT3475/LT3475-1
ELECTRICAL CHARACTERISTICS
PARAMETER
LED Pin Current
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V, V
BOOST
= 16V, V
OUT
= 4V unless otherwise noted (Note 3)
CONDITIONS
V
ADJ
Tied to V
REF
• 2/3
V
ADJ
Tied to V
REF
• 7/30
LT3475E/LT3475E-1 0°C to 85°C
●
●
MIN
0.97
0.94
0.336
0.325
0.31
1.22
TYP
1.00
0.350
MAX
1.03
1.04
0.364
0.375
0.385
1.27
UNITS
A
A
A
A
A
V
%/V
%/μA
REF Voltage
Reference Voltage Line Regulation
Reference Voltage Load Regulation
V
ADJ
Pin Bias Current (Note 4)
Switching Frequency
Maximum Duty Cycle
R
T
= 24.3k
R
T
= 24.3k
R
T
= 4.32k
R
T
= 100k
R
T
= 24.3k
R
T
= 24.3k, V
OUT
= 0V
4V < V
IN
< 40V
0 < I
REF
< 500μA
●
1.25
0.05
0.0002
●
●
●
40
530
90
600
95
80
98
180
80
2.5
2.6
9
0.8
0.8
50
50
500
1
2.6
1.8
400
640
nA
kHz
%
%
%
Switching Phase
Foldback Frequency
SHDN Threshold (to Switch)
SHDN Pin Current (Note 5)
PWM Threshold
V
C
Switching Threshold
V
C
Source Current
V
C
Sink Current
LED to V
C
Transresistance
LED to V
C
Current Gain
V
C
to Switch Current Gain
V
C
Clamp Voltage
V
C
Pin Current in PWM Mode
OUT Pin Clamp Voltage (LT3475)
OUT Pin Current in PWM Mode
Switch Current Limit (Note 6)
Switch V
CESAT
BOOST Pin Current
Switch Leakage Current
Minimum Boost Voltage Above SW
150
210
2.74
11
1.2
Deg
kHz
V
μA
V
V
μA
μA
V/A
mA/μA
A/V
V
V
SHDN
= 2.6V
7
0.3
V
C
= 1V
V
C
= 1V
V
C
= 1V, V
PWM
= 0.3V
V
OUT
= 4V, V
PWM
= 0.3V
I
SW
=1.5A
I
SW
=1.5A
●
10
13.5
14
25
2.3
2.7
350
25
0.1
1.8
400
14.5
50
3.2
500
40
10
2.5
nA
V
μA
A
mV
mA
μA
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:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
Note 3:
The LT3475E and LT3475E-1 are guaranteed to meet performance
specifications from 0°C to 85°C. Specifications over the –40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls. The LT3475I and LT3475I-1
are guaranteed to meet performance specifications over the –40°C to
125°C operating temperature range.
Note 4:
Current flows out of pin.
Note 5:
Current flows into pin.
Note 6:
Current limit is guaranteed by design and/or correlation to static
test. Slope compensation reduces current limit at higher duty cycles.
3475fb
3
LT3475/LT3475-1
TYPICAL PERFOR A CE CHARACTERISTICS
LED Current vs V
ADJ
1.50
1.25
LED CURRENT (A)
LED CURRENT (A)
1.00
0.75
0.50
0.25
0
0
0.25
0.5
0.75
V
ADJ
(V)
1
1.25
3475 G01
T
A
= 25°C
SWITCH ON VOLTAGE (mV)
Switch Current Limit
vs Duty Cycle
3.0
2.5
CURRENT LIMIT (A)
2.0
1.5
1.0
0.5
0
0
20
40
60
DUTY CYCLE (%)
T
A
= 25°C
80
100
3475 G04
TYPICAL
CURRENT LIMIT (A)
CURRENT LIMIT (A)
MINIMUM
Oscillator Frequency
vs Temperature
700
OSCILLATOR FREQUENCY (kHz)
650
600
550
500
450
400
–50 –25
R
T
= 24.3kΩ
OSCILLATOR FREQUENCY (kHz)
700
600
500
400
300
200
100
0
50
25
75
0
TEMPERATURE (˚C)
100
125
OSCILLATOR FREQUENCY (kHz)
4
U W
LED Current vs Temperature
1.2
V
ADJ
= V
REF
• 2/3
1.0
0.8
0.6
0.4
0.2
0
–50 –25
V
ADJ
= V
REF
• 7/30
600
500
400
300
200
100
0
50
25
75
0
TEMPERATURE (˚C)
100
125
Switch On Voltage
T
A
= 25°C
0
1.5
0.5
1.0
SWITCH CURRENT (A)
2.0
3475 G03
3475 G02
Switch Current Limit vs
Temperature
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
–50 –25
3.0
2.5
2.0
1.5
1.0
0.5
0
Current Limit vs Output Voltage
T
A
= 25°C
50
25
75
0
TEMPERATURE (°C)
100
125
0
0.5
1.0
1.5 2.0 2.5
V
OUT
(V)
3.0
3.5
4.0
3475 G05
3475 G06
Oscillator Frequency Foldback
T
A
= 25°C
R
T
= 24.3kΩ
1000
Oscillator Frequency vs R
T
T
A
= 25°C
10
0
0.5
1.0
1.5
2.0
2.5
3475 G08
1
V
OUT
(V)
3475 G07
10
R
T
(kΩ)
100
3475 G09
3475fb
LT3475/LT3475-1
TYPICAL PERFOR A CE CHARACTERISTICS
Boost Pin Current
35
30
BOOST PIN CURRENT (mA)
INPUT CURRENT (mA)
25
20
15
10
5
0
0
0.5
1.5
SWITCH CURRENT (A)
1.0
2.0
3475 G10
T
A
= 25°C
5
4
3
2
1
0
0
10
20
V
IN
(V)
3475 G11
OUTPUT VOLTAGE (V)
Reference Voltage
1.28
1.27
1.26
V
REF
(V)
1.25
1.24
1.23
1.22
–50 –25
V
IN
(V)
6
5
4
3
2
1
0
V
IN
(V)
50
25
75
0
TEMPERATURE (˚C)
PI FU CTIO S
OUT1, OUT2 (Pins 1, 10):
The OUT pin is the input to the
current sense resistor. Connect this pin to the inductor
and the output capacitor.
LED1, LED2 (Pins 2, 9):
The LED pin is the output of
the current sense resistor. Connect the anode of the LED
here.
V
IN
(Pins 5, 6):
The V
IN
pins supply current to the internal
circuitry and to the internal power switches and must be
locally bypassed.
SW1, SW2 (Pins 4, 7):
The SW pin is the output of the
internal power switch. Connect this pin to the inductor,
switching diode and boost capacitor.
3475fb
U W
100
3475 G13
Quiescent Current
7
6
T
A
= 25°C
50
45
40
35
30
25
20
15
10
5
30
40
0
Open-Circuit Output Voltage and
Input Current
T
A
= 25°C
14
INPUT CURRENT
LT3475-1
12
INPUT CURRENT (mA)
10
LT3475
8
LT3475-1
OUTPUT VOLTAGE
LT3475
6
4
2
0
0
10
20
V
IN
(V)
30
40
3475 G12
Minimum Input Voltage, Single
1.5A White LED
T
A
= 25°C
TO START
9
TO RUN
10
Minimum Input Voltage, Two Series
Connected 1.5A White LEDs
T
A
= 25°C
LED VOLTAGE
8
TO START
LED VOLTAGE
TO RUN
7
6
125
5
0
0.5
1
LED CURRENT (A)
1.5
3475 G14
0
0.5
1
LED CURRENT (A)
1.5
3475 G15
U
U
U
BOOST1, BOOST2 (Pins 3, 8):
The BOOST pin is used to
provide a drive voltage, higher than the input voltage, to
the internal bipolar NPN power switch.
GND (Pins 15, Exposed Pad Pin 21):
Ground. Tie the GND
pin and the exposed pad directly to the ground plane. The
exposed pad metal of the package provides both electrical
contact to ground and good thermal contact to the printed
circuit board. The exposed pad must be soldered to the
circuit board for proper operation. Use a large ground plane
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