LT3465/LT3465A
1.2MHz/2.4MHz White LED
Step-Up Converters with
Built-In Schottky in ThinSOT
FEATURES
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DESCRIPTIO
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Inherently Matched LED Current
Drives Up to Six LEDs from a 3.6V Supply
No External Schottky Diode Required
1.2MHz Switching Frequency (LT3465)
2.4MHz Switching Frequency Above AM Broadcast
Band (LT3465A)
Automatic Soft-Start (LT3465)
Open LED Protection
High Efficiency: 81% (LT3465) 79% (LT3465A)
Typical
Requires Only 0.22µF Output Capacitor
Low Profile (1mm) SOT-23 Packaging
The LT
®
3465/LT3465A are step-up DC/DC converters
designed to drive up to six LEDs in series from a Li-Ion cell.
Series connection of the LEDs provides identical LED
currents and eliminates the need for ballast resistors.
These devices integrate the Schottky diode required exter-
nally on competing devices. Additional features include
output voltage limiting when LEDs are disconnected, one-
pin shutdown and dimming control. The LT3465 has
internal soft-start.
The LT3465 switches at 1.2MHz, allowing the use of tiny
external components. The faster LT3465A switches at
2.4MHz. Constant frequency switching results in low input
noise and a small output capacitor. Just 0.22µF is required
for 3-, 4- or 5-LED applications.
The LT3465 and LT3465A are available in low profile
(1mm) 6-lead SOT-23 (ThinSOT
TM
) packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
APPLICATIO S
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Cellular Phones
PDAs, Handheld Computers
Digital Cameras
MP3 Players
GPS Receivers
TYPICAL APPLICATIO
L1
22µH
3V TO 5V
Conversion Efficiency
V
IN
= 3.6V
80 4 LEDs
78
EFFICIENCY (%)
SW
V
IN
SHUTDOWN
AND DIMMING
CONTROL
C1
1µF
LT3465/
LT3465A
CTRL
FB
GND
C2
0.22µF
10Ω
3465A F01a
82
V
OUT
76
74
72
70
68
66
64
62
60
0
5
10
LED CURRENT (mA)
3465A F01b
C1, C2: X5R OR X7R DIELECTRIC
L1: MURATA LQH32CN220
Figure 1. Li-Ion Powered Driver for Four White LEDs
U
LT3465
LT3465A
15
20
3465af
U
U
1
LT3465/LT3465A
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
OUT
1
GND 2
FB 3
6 SW
5 V
IN
4 CTRL
Input Voltage (V
IN
) ................................................. 16V
SW Voltage ............................................................. 36V
FB Voltage ................................................................ 2V
CTRL Voltage .......................................................... 10V
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Maximum Junction Temperature ......................... 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
LT3465ES6
LT3465AES6
S6 PART MARKING
LTH2
LTAFT
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
T
JMAX
= 125°C,
θ
JA
= 256°C/W IN FREE AIR
θ
JA
= 120°C ON BOARD OVER GROUND PLANE
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER
Minimum Operating Voltage
Maximum Operating Voltage
Feedback Voltage
FB Pin Bias Current
Supply Current
Switching Frequency
Maximum Duty Cycle
Switch Current Limit
Switch V
CESAT
Switch Leakage Current
V
CTRL
for Full LED Current
V
CTRL
to Shut Down Chip
CTRL Pin Bias Current
T
A
= 85°C
T
A
= –40°C
Soft-Start Time
Schottky Forward Drop
Schottky Leakage Current
I
D
= 150mA
V
R
= 30V
I
SW
= 250mA
V
SW
= 5V
Not Switching
CTRL = 0V
0°C
≤
T
A
≤
85°C
CONDITIONS
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3V, V
CTRL
= 3V, unless otherwise noted.
MIN
2.7
16
188
10
1.9
2.0
0.8
q
q
LT3465
TYP
MAX
MIN
2.7
LT3465A
TYP
MAX
16
UNITS
V
V
mV
nA
mA
µA
MHz
%
mA
mV
200
35
2.6
3.2
1.2
93
340
300
0.01
212
100
3.3
5.0
1.6
188
10
1.9
2.0
1.8
90
225
200
35
2.6
3.2
2.4
93
340
300
0.01
212
100
3.3
5.0
2.8
90
225
5
1.8
50
5
50
1.8
48
40
60
60
50
75
600
0.7
4
72
60
90
48
40
60
60
50
75
0.7
72
60
90
4
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LT3465E/LT3465AE are guaranteed to meet performance
specifications from 0°C to 70°C. Specifications over the –40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
2
U
µA
V
mV
µA
µA
µA
µs
V
µA
3465af
W
U
U
W W
W
LT3465/LT3465A
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Saturation Voltage (V
CESAT
)
450
SWITCH SATURATION VOLTAGE (mV)
T
A
= 25°C
SCHOTTKY FORWARD CURRENT (mA)
400
350
300
250
200
150
100
50
0
0
50
100 150 200 250
SWITCH CURRENT (mA)
300
350
150
100
50
0
I
Q
(µA)
V
FB
vs V
CTRL
250
T
A
= 25°C
OUTPUT CLAMP VOLTAGE (V)
FEEDBACK VOLTAGE (mV)
200
25
20
15
10
5
INPUT CURRENT (mA)
150
100
50
0
0
1
0.5
1.5
CONTROL VOLTAGE (V)
Switching Waveforms (LT3465)
V
SW
10V/DIV
I
L
100mA/DIV
V
OUT
100mV/DIV
V
SW
10V/DIV
I
L
50mA/DIV
V
OUT
50mV/DIV
V
IN
= 3.6V
4 LEDs
20mA, 22µH
200ns/DIV
SWITCHING FREQUENCY (MHz)
U W
3465A G01
Schottky Forward Voltage Drop
300
250
200
T
A
= 25°C
Shutdown Quiescent Current
(CTRL = 0V)
30
27
24
21
18
15
12
9
6
3
T
A
= 25°C
0
1000
400
600
800
200
SCHOTTKY FORWARD DROP (mV)
1200
0
2
4
6
10
8
V
IN
(V)
12
14
16
3465A G02
3465A G03
Open-Circuit Output Clamp Voltage
35
30
Input Current in Output Open Circuit
5
T
A
= 25°C
T
A
= 25°C
4
3
2
1
0
0
2
4
10
8
12
6
INPUT VOLTAGE (V)
14
16
2
3465A G04
2
2.5
4
3
3.5
INPUT VOLTAGE (V)
4.5
5
3465A G05
3465A G06
Switching Waveforms (LT3465A)
3.0
2.5
2.0
1.5
Switching Frequency
LT3465A
LT3465
1.0
0.5
0
–50
3465A G07a
V
IN
= 3.6V
4 LEDs
20mA, 22µH
100ns/DIV
3465A G07b
50
0
TEMPERATURE (°C)
100
4365A G08
3465af
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LT3465/LT3465A
TYPICAL PERFOR A CE CHARACTERISTICS
Feedback Voltage
210
208
FEEDBACK VOLTAGE (mV)
3.0
2.5
2.0
I
Q
(mA)
206
204
202
200
198
196
194
192
190
–50 –30 –10 10 30 50
TEMPERATURE (°C)
CURRENT LIMIT (mA)
–50°C
25°C
100°C
0
5
10
V
IN
(V)
15
20
3465A G10
V
IN
= 3.6V, 4 LEDs
85
SCHOTTKY LEAKAGE CURRENT (µA)
LT3465
LT3465A
80
EFFICIENCY (%)
75
15mA
10mA
70
65
60
–50
50
0
TEMPERATURE (°C)
PI FU CTIO S
V
OUT
(Pin 1):
Output Pin. Connect to output capacitor and
LEDs. Minimize trace between this pin and output capaci-
tor to reduce EMI.
GND (Pin 2):
Ground Pin. Connect directly to local ground
plane.
FB (Pin 3):
Feedback Pin. Reference voltage is 200mV.
Connect LEDs and a resistor at this pin. LED current is
determined by the resistance and CTRL pin voltage:
200mV
When V
CTRL
>
1.8 V
R
FB
V
I
LED
≈
CTRL
When V
CTRL
<
1V
5 • R
FB
I
LED
≈
3465af
4
U W
70
90
3465A G09
Quiescent Current (CTRL = 3V)
400
350
300
250
200
150
100
50
0
Switching Current Limit
1.5
1.0
0.5
0
–50°C
25°C
100°C
0
20
40
60
DUTY CYCLE (%)
80
100
3465A G11
Schottky Leakage Current
8
20mA
7
V
R
= 25
6
5
4
3
2
1
0
–50
0
50
100
3465A G13
V
R
= 16
V
R
= 10
100
3465A G12
TEMPERATURE (°C)
U
U
U
CTRL (Pin 4):
Dimming Control and Shutdown Pin. Ground
this pin to shut down the device. When V
CTRL
is greater
than about 1.8V, full-scale LED current is generated. When
V
CTRL
is less than 1V, LED current is reduced.
V
IN
(Pin 5):
Input Supply Pin. Must be locally bypassed
with a 1µF X5R or X7R type ceramic capacitor.
SW (Pin 6):
Switch Pin. Connect inductor here.
LT3465/LT3465A
BLOCK DIAGRA
V
IN
5
A1
R
C
C
C
Σ
10k
RAMP
GENERATOR
40k
CTRL
4
1.2MHz*
OSCILLATOR
Figure 2. LT3465 Block Diagram
APPLICATIO S I FOR ATIO
Operation
The LT3465 uses a constant frequency, current mode
control scheme to provide excellent line and load regula-
tion. Operation can be best understood by referring to the
block diagram in Figure 2. At the start of each oscillator
cycle, the SR latch is set, which turns on the power switch
Q1. A voltage proportional to the switch current is added
to a stabilizing ramp and the resulting sum is fed into the
positive terminal of the PWM comparator A2. When this
voltage exceeds the level at the negative input of A2, the
SR latch is reset turning off the power switch. The level at
the negative input of A2 is set by the error amplifier A1,
and is simply an amplified version of the difference
between the feedback voltage and the reference voltage of
200mV. In this manner, the error amplifier sets the
correct peak current level to keep the output in regulation.
If the error amplifier’s output increases, more current is
delivered to the output; if it decreases, less current is
delivered. The CTRL pin voltage is used to adjust the
reference voltage. The block diagram for the LT3465A (not
shown) is identical except that the oscillator frequency is
2.4MHz.
Minimum Output Current
The LT3465 can drive a 3-LED string at 1.5mA LED
current without pulse skipping. As current is further
reduced, the device will begin skipping pulses. This will
+
–
V
REF
1.25V
U
W
W
FB
3
6 SW
COMPARATOR
DRIVER
A2
R
S
Q
Q1
OVERVOLTAGE
PROTECT
200mV
–
+
+
V
OUT
1
+
0.2Ω
–
2 GND
3465A F02
*2.4MHz FOR LT3465A
U U
result in some low frequency ripple, although the LED
current remains regulated on an average basis down to
zero. The photo in Figure 3a details circuit operation
driving three white LEDs at a 1.5mA load. Peak inductor
current is less than 40mA and the regulator operates in
discontinuous mode, meaning the inductor current
V
SW
5V/DIV
I
L
20mA/DIV
V
OUT
10mV/DIV
V
IN
= 4.2V
I
LED
= 1.5mA
3 LEDs
0.2µs/DIV
3465A F03a
Figure 3a. Switching Waveforms (LT3465)
V
SW
5V/DIV
I
L
20mA/DIV
V
OUT
10mV/DIV
V
IN
= 4.2V
I
LED
= 0.2mA
3 LEDs
0.1µs/DIV
3465A F03b
Figure 3b. Switching Waveforms (LT3465A)
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