LT3465A
1
3465ai
, LTC and LT are registered trademarks of Linear Technology Corporation.
■
Inherently Matched LED Current
■
Drives Up to Six LEDs from a 3.6V Supply
■
No External Schottky Diode Required
■
Open LED Protection
■
High Efficiency: 79% Typical
■
Requires Only 0.22µF Output Capacitor
■
Switching Frequency Above AM Broadcast Band
■
Low Profile (<1mm) SOT-23 Packaging
2.4MHz White LED Step-Up
Converter with Built-In
Schottky in ThinSOT
TM
August 2003
■
Cellular Phones
■
PDAs, Handheld Computers
■
Digital Cameras
■
MP3 Players
■
GPS Receivers
DESCRIPTIO
U
FEATURES
APPLICATIO S
U
TYPICAL APPLICATIO
U
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
Final Electrical Specifications
The LT
®
3465A is a step-up DC/DC converter 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. This device
integrates the Schottky diode required externally on com-
peting devices. Additional features include output voltage
limiting when LEDs are disconnected, one-pin shutdown
and dimming control.
The LT3465A switches at 2.4MHz, allowing the use of tiny
external components. Constant frequency switching re-
sults in low input noise and a small output capacitor. Just
0.22µF is required for 3-, 4- or 5-LED applications.
The LT3465A is available in a low profile (<1mm) 6-lead
SOT-23 package.
ThinSOT is a trademark of Linear Technology Corporation.
Figure 1. Li-Ion Powered Driver for Four White LEDs
SW V
OUT
V
IN
LT3465A
CTRL
3465A F01a
R1
10Ω
C1
1µFC2
0.22µF
C1, C2: X5R OR X7R DIELECTRIC
L1: MURATA LQH32CN220
L1
22µH
3V TO 5V
SHUTDOWN
AND DIMMING
CONTROL FB
GND
Conversion Efficiency
LED CURRENT (mA)
0
EFFICIENCY (%)
20
3465A F01b
510 15
80
78
76
74
72
70
68
66
64
62
60
V
IN
= 3.6V
LT3465A
2
3465ai
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
(Note 1)
ABSOLUTE AXI U RATI GS
WWWU
PACKAGE/ORDER I FOR ATIO
UU
W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
LT3465AES6
T
JMAX
= 125°C, θ
JA
= 256°C/W IN FREE AIR
θ
JA
= 120°C ON BOARD OVER GROUND PLANE
θ
JC
= 102°C/W
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3V, VCTRL = 3V, unless otherwise noted.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Operating Voltage 2.7 V
Maximum Operating Voltage 16 V
Feedback Voltage 0°C ≤ T
A
≤ 85°C 188 200 212 mV
FB Pin Bias Current 10 35 100 nA
Supply Current Not Switching 1.9 2.6 3.3 mA
CTRL = 0V 2.0 3.2 5.0 µA
Switching Frequency 1.8 2.4 2.8 MHz
Maximum Duty Cycle ●90 93 %
Switch Current Limit ●225 340 mA
Switch V
CESAT
I
SW
= 250mA 300 mV
Switch Leakage Current V
SW
= 5V 0.01 5 µA
V
CTRL
for Full LED Current 1.8 V
V
CTRL
to Shut Down Device 50 mV
CTRL Pin Bias Current 48 60 72 µA
T
A
= 85°C 405060 µA
T
A
= –40°C 607590 µA
Schottky Forward Drop I
D
= 150mA 0.7 V
Schottky Leakage Current V
R
= 30V 4 µA
ELECTRICAL CHARACTERISTICS
V
OUT
1
GND 2
TOP VIEW
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
FB 3
6 SW
5 V
IN
4 CTRL
S6 PART MARKING
LTAFT
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LT3465AE is 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.
LT3465A
3
3465ai
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Switch Saturation Voltage (VCESAT) Schottky Forward Voltage Drop Shutdown Quiescent Current
(CTRL = 0V)
SWITCH CURRENT (mA)
0
0
SWITCH SATURATION VOLTAGE (mV)
50
150
200
250
200
450
3465 G01
100
100
50 250 300
150 350
300
350
400
T
A
= 25°C
SCHOTTKY FORWARD DROP (mV)
0
0
SCHOTTKY FORWARD CURRENT (mA)
50
100
150
200
300
200 400 600 800
3465 G02
1000 1200
250
TA = 25°C
V
IN
(V)
2
I
Q
(µA)
12
15
18
814
3465 G03
9
6
3
04 6 10 12
21
24
27
30
16
T
A
= 25°C
VFB vs VCTRL Open-Circuit Output Clamp Voltage
CONTROL VOLTAGE (V)
0
FEEDBACK VOLTAGE (mV)
100
150
2
3465 G04
50
00.5 11.5
250
200
T
A
= 25°C
INPUT VOLTAGE (V)
2
20
25
35
812
3465 G05
15
10
46 10 14 16
5
0
30
OUTPUT CLAMP VOLTAGE (V)
T
A
= 25°C
Input Current in Output Open Circuit
Switching Waveforms
V
SW
10V/DIV
I
L
50mA/DIV
V
OUT
50mV/DIV
V
IN
= 3.6V 100ns/DIV 3465 G07
4 LEDs
20mA, 22µH
Switching Frequency
TEMPERATURE (°C)
–50
190
FEEDBACK VOLTAGE (mV)
192
196
198
200
210
204
–10 30 50
3465 G09
194
206
208
202
–30 10 70 90
Feedback Voltage
INPUT VOLTAGE (V)
2.0
INPUT CURRENT (mA)
5
4
3
2
1
02.5 3.0 3.5 4.0
3465 G06
4.5 5.0
TEMPERATURE (°C)
–50
SWITCHING FREQUENCY (MHz)
3.0
2.5
2.0
1.5
1.0
0.5
00 50 100
3465 G08
LT3465A
4
3465ai
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Quiescent Current (CTRL = 3V)
V
IN
(V)
0
0
I
Q
(mA)
0.5
1.0
1.5
2.0
2.5
3.0
5101520
3465 G10
–50°C
25°C
100°C
DUTY CYCLE (%)
0
CURRENT LIMIT (mA)
150
200
250
60 100
3465 G11
100
50
020 40 80
300
350
400
–50°C
25°C
100°C
Switching Current Limit
VIN = 3.6V, 4 LEDs
UU
U
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:
ImV
RWhen V V
IV
RWhen V V
LED FB CTRL
LED CTRL
FB CTRL
≈>
≈<
200 18
51
.
•
(1)
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.
TEMPERATURE (°C)
–50
SCHOTTKY LEAKAGE CURRENT (µA)
3
4
V
R
= 25
V
R
= 16
V
R
= 10
5
3465 G13
2
1
0050
6
7
8
100
Schottky Leakage Current
TEMPERATURE (°C)
–50
EFFICIENCY (%)
3465A G12
050 100
80
79
78
77
76
75
74
73
72
71
70
20mA
15mA
10mA
LT3465A
5
3465ai
BLOCK DIAGRA
W
–
+
+
–
+
RQ
S
0.2Ω
SW
DRIVER
COMPARATOR
2
CTRL
4
6V
OUT
V
IN
3
FB
200mV
5
–
+
Σ
RAMP
GENERATOR
R
C
10k
40k
C
C
2.4MHz
OSCILLATOR
GND
3465A F02
Q1
A2
A1
V
REF
1.25V 1
Figure 2. LT3465A Block Diagram
APPLICATIO S I FOR ATIO
WUUU
Operation
The LT3465A 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.
Minimum Output Current
T
he LT3465A can drive a 3-LED string at 0.2mA LED
current without pulse skipping. As current is further
reduced, the device may begin skipping pulses. This will
result in some low frequency ripple, although the LED
current remains regulated on an average basis down to
zero. The photo in Figure 3 details circuit operation
driving three white LEDs at a 0.2mA load. Peak inductor
current is less than 30mA and the regulator operates in
discontinuous mode, meaning the inductor current
reaches zero during the discharge phase. After the induc-
tor current reaches zero, the SW pin exhibits ringing due
to the LC tank circuit formed by the inductor in combina-
tion with switch and diode capacitance. This ringing is
not harmful; far less spectral energy is contained in the
ringing than in the switch transitions. The ringing can be
damped by application of a 300Ω resistor across the
inductor, although this will degrade efficiency.
V
SW
5V/DIV
I
L
20mA/DIV
V
OUT
10mV/DIV
V
IN
= 4.2V 0.1µs/DIV 3465A F03
I
LED
= 0.2mA
3 LEDs
Figure 3. Switching Waveforms
LT3465A
6
3465ai
APPLICATIO S I FOR ATIO
WUUU
Inductor Selection
A 22µH or 10µH inductor is recommended for most
LT3465A applications. Although small size and high effi-
ciency are major concerns, the inductor should have low
core losses at 1.2MHz and low DCR (copper wire resis-
tance). Some inductors in this category with small size are
listed in Table␣ 1. The efficiency comparison of different
inductors is shown in Figure 4.
Table 1. Recommended Inductors
PART CURRENT RATING
NUMBER DCR (Ω) (mA) MANUFACTURER
LQH32CN220 0.71 250 Murata
814-237-1431
www.murata.com
ELJPC220KF 4.0 160 Panasonic
714-373-7334
www.panasonic.com
CDRH3D16-220 0.53 350 Sumida
847-956-0666
www.sumida.com
LB2012B220M 1.7 75 Taiyo Yuden
408-573-4150
www.t-yuden.com
LEM2520-220 5.5 125 Taiyo Yuden
408-573-4150
www.t-yuden.com
Capacitor Selection
The small size of ceramic capacitors makes them ideal for
LT3465A applications. X5R and X7R types are recom-
mended because they retain their capacitance over wider
voltage and temperature ranges than other types such as
Y5V or Z5U. A 1µF input capacitor and a 0.22µF output
capacitor are sufficient for most LT3465A applications.
Table 2. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER PHONE URL
Taiyo Yuden 408-573-4150 www.t-yuden.com
Murata 814-237-1431 www.murata.com
Kemet 408-986-0424 www.kemet.com
Inrush Current
The LT3465A has a built-in Schottky diode. When supply
voltage is applied to the V
IN
pin, the voltage difference
between V
IN
and V
OUT
generates inrush current flowing
from input through the inductor and the Schottky diode to
charge the output capacitor to V
IN
. The maximum current
the Schottky diode in the LT3465A can sustain is 1A. The
selection of inductor and capacitor value should ensure
the peak of the inrush current to be below 1A. The peak
inrush current can be calculated as follows:
IV
Laa
r
L
LC
r
L
PIN
=
=+
=+
()
–.
••exp – • tan •sin tan
.
•
•–.
•
06
15
2
115
4
2
2
ωα
ωω
αω
α
α
ω
where L is the inductance, r is the resistance of the
inductor and C is the output capacitance. For low DCR
inductors, which is usually the case for this application,
the peak inrush current can be simplified as follows:
IV
L
PIN
=
–.
••exp – •
06
2ωα
ωπ
Figure 4. Efficiency Comparison of Different Inductors
LED CURRENT (mA)
0
70
75
15
3465 F04
65
60
510 20
55
50
80
EFFICIENCY (%)
VIN = 3.6V
4 LEDS
MURATA LQH32CN220
MURATA LQH32CN100
MURATA LQH2MCN220
TOKO D312-220
TOKO D312-100
TAIYO YUDEN LB2012B220
LT3465A
7
3465ai
Table 3 gives inrush peak currents for some component
selections.
Table 3. Inrush Peak Current
V
IN
(V) r (Ω)L (µH) C (µF) I
P
(A)
5 0.5 22 0.22 0.38
5 0.5 22 1 0.70
3.6 0.5 22 0.22 0.26
5 0.5 33 1 0.60
LED Current and Dimming Control
The LED current is controlled by the feedback resistor (R1
in Figure 1) and the feedback reference voltage.
I
LED
= V
FB
/R
FB
The CTRL pin sets the feedback reference voltage as
shown in the Typical Performance Characteristics. When
CTRL is at 1.8V or more, the feedback reference is 200mV,
which results in full-scale LED current. The CTRL pin can
be used as a dimming control when its voltage is between
200mV to 1.5V. To maintain LED current accuracy, a 1%
or better resistor for R1 is recommended. The formula and
table for R
FB
selection are shown below:
R
FB
= 200mV/I
LEDF
where I
LEDF
is full-scale LED current
Table 4. RFB Resistor Value Selection
I
LED
(mA) R1 (Ω)
5 40.2
10 20.0
15 13.3
20 10.0
Dimming Using Filtered PWM
Dimming can be realized by using an RC filter in front of the
CTRL pin to filter a PWM signal, as depicted in Figure 5.
The filtered PWM signal is equivalent to a constant volt-
age. The time constant R1 • C1 should be much lower than
the frequency of the PWM signal. Additionally, R1 should
be small compared to the 50kΩ impedance of the CTRL
pin. Suggested values are shown in Figure 5.
APPLICATIO S I FOR ATIO
WUUU
Dimming Using Direct PWM
Unlike the LT3465, the LT3465A does not have internal
soft-start. Although the input current is higher during
start-up, the absence of soft-start allows the CTRL pin to
be directly driven with a PWM signal for dimming. A zero
percent duty cycle sets the LED current to zero, while
100% duty cycle sets it to full current. Average LED current
increases proportionally with the duty cycle of the PWM
signal. PWM frequency should be between 1kHz and
10kHz for best performance. The PWM signal should be at
least 1.8V in magnitude; lower voltage will lower the
feedback voltage as shown in Equation 1. Waveforms are
shown for a 1kHz PWM and 10kHz PWM signal in Figures
6a and 6b respectively.
LT3465
CTRL
3465 F06
PWM C1
100nF
R1
5k
Figure 5. Dimming Control Using a Filtered PWM Signal
Figure 6a.
Figure 6b.
FB
100mV/DIV
CTRL
2V/DIV
200µs/DIV (1kHz) 3465A F06a
FB
100mV/DIV
CTRL
2V/DIV
20µs/DIV (10kHz) 3465A F06b
LT3465A
CTRLPWM
LT3465A
8
3465ai
APPLICATIO S I FOR ATIO
WUUU
Figure 7. Recommended Component Placement
Open Circuit Protection
The LT3465A has an internal open-circuit protection cir-
cuit. When the LEDs are disconnected from the circuit or
fail open, V
OUT
is clamped at 30V. The LT3465A will then
switch at a low frequency, minimizing input current. V
OUT
and input current during open circuit are shown in the
Typical Performance Characteristics.
Board Layout Consideration
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
To maximize efficiency, switch rise and fall times are made
as short as possible. To prevent electromagnetic interfer-
ence (EMI) problems, proper layout of the high frequency
1
C
OUT
L
R
FB
2
3
6
5
4
C
IN
GND
3465 F07
V
IN
CTRL
switching path is essential. Place C
OUT
next to the V
OUT
pin. Always use a ground plane under the switching
regulator to minimize interplane coupling. In addition, the
ground connection for the feedback resistor R1 should be
tied directly to the GND pin and not shared with any other
component, ensuring a clean, noise-free connection. Rec-
ommended component placement is shown in Figure 7.
Start-Up Input Current
As previously mentioned, the LT3465A does not have an
internal soft-start circuit. Inrush current can therefore rise
to approximately 400mA as shown in Figure 8 when
driving 4 LEDs. The LT3465 has an internal soft-start
circuit and is recommended if inrush current must be
minimized.
Figure 8.
FB
200mV/DIV
CTRL
2V/DIV
50µs/DIV 3465A F06b
I
IN
200mV/DIV
LT3465A
9
3465ai
SW V
OUT
V
IN
LT3465A
CTRL
3465 TA02a
R1
10Ω
C
IN
1µFC
OUT
0.22µF
L1
22µH
3V TO 5V
FB
GND
C
IN
: TAIYO YUDEN JMK107BJ105
C
OUT
: AVX 0603YD224
L1: MURATA LQH32CN220
Li-Ion to Two White LEDs
SW V
OUT
V
IN
LT3465A
CTRL
3465 TA01a
R1
4Ω
C
IN
1µFC
OUT
1µF
C
IN
: TAIYO YUDEN JMK107BJ105
C
OUT
: AVX 0603ZD105
L1: MURATA LQH32CN220
L1
22µH
3V TO 5V
FB
GND
Li-Ion to Three White LEDs
LED CURRENT (mA)
0
EFFICIENCY (%)
75
80
85
40
3465 TA01b
70
65
60
55
50 10 20 30 50
V
IN
= 3.6V
2 LEDS
LED CURRENT (mA)
0
EFFICIENCY (%)
75
80
85
3465 TA02b
70
65
60
55
50 510 15 20
VIN = 3.6V
3 LEDS
TYPICAL APPLICATIO S
U
LT3465A
10
3465ai
TYPICAL APPLICATIO S
U
Li-Ion to Five White LEDs
SW V
OUT
V
IN
LT3465A
CTRL
3465 TA03a
R1
10Ω
C
IN
1µFC
OUT
0.22µF
L1
22µH
3V TO 5V
FB
GND
C
IN
: TAIYO YUDEN JMK107BJ105
C
OUT
: TAIYO YUDEN GMK212BJ224
L1: MURATA LQH32CN220
LED CURRENT (mA)
0
EFFICIENCY (%)
75
80
3465 TA03b
70
65
60
55
50 510 15 20
VIN = 3.6V
5 LEDS
LT3465A
11
3465ai
U
PACKAGE DESCRIPTIO
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
1.50 – 1.75
(NOTE 4)
2.80 BSC
0.30 – 0.45
6 PLCS (NOTE 3)
DATUM ‘A’
0.09 – 0.20
(NOTE 3)
S6 TSOT-23 0302
2.90 BSC
(NOTE 4)
0.95 BSC
1.90 BSC
0.80 – 0.90
1.00 MAX 0.01 – 0.10
0.20 BSC
0.30 – 0.50 REF
PIN ONE ID
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
3.85 MAX
0.62
MAX 0.95
REF
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
1.4 MIN
2.62 REF
1.22 REF
LT3465A
12
3465ai
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
LINEAR TECHNOLO GY CORPORATION 2003
Li-Ion to Six White LEDs
SW V
OUT
V
IN
LT3465A
CTRL
3465 TA04a
R1
10Ω
C
IN
1µFC
OUT
0.47µF
L1
22µH
3V TO 5V
FB
GND
C
IN
: TAIYO YUDEN JMK107BJ105
C
OUT
: TDK 2012X7R1E474K
L1: MURATA LQH32CN220
LT/TP 0803 1.5K • PRINTED IN USA
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), 1.4MHz Synchronous Step-Down 95% Efficiency, V
IN
: 2.7V to 6V, V
OUT(MIN)
: 0.8V, I
Q
: 10µA, I
SD
: <1µA,
DC/DC Converter MS8 Package
LTC3405 300mA (I
OUT
), 1.5MHz Synchronous Step-Down 95% Efficiency, V
IN
: 2.7V to 6V, V
OUT(MIN)
: 0.8V, I
Q
: 20µA, I
SD
: <1µA,
LTC3405A DC/DC Converters ThinSOT Package
LTC3406 600mA (I
OUT
), 1.5MHz Synchronous Step-Down 95% Efficiency, V
IN
: 2.5V to 5.5V, V
OUT(MIN)
: 0.6V, I
Q
: 20µA,
LTC3406B DC/DC Converters I
SD
: <1µA, ThinSOT Package
LT3407 Dual 600mA (I
OUT
), 1.5MHz Synchronous Step-Down 96% Efficiency, V
IN
: 2.5V to 5.5V, V
OUT(MIN)
: 0.6V, I
Q
: 40µA,
DC/DC Converter I
SD
: <1µA, MS Package
LTC3412 2.5A (I
OUT
), 4MHz Synchronous Step-Down DC/DC Converter 95% Efficiency, V
IN
: 2.5V to 5.5V, V
OUT(MIN)
: 0.8V, I
Q
: 60µA,
I
SD
: <1µA, TSSOP16E Package
LTC3440 600mA (I
OUT
), 2MHz Synchronous Buck-Boost 95% Efficiency, V
IN
: 2.5V to 5.5V, V
OUT(MIN)
: 2.5V, I
Q
: 25µA,
DC/DC Converter I
SD
: <1µA, 10-Lead MS Package
LTC3465 Constant Current, 1.2MHz, High Efficiency White LED Up to 5 White LEDs, V
IN
: 2.7V to 16V, I
Q
: 1.9A,
Boost Regulator I
SD
: <1µA, ThinSOT Package
TYPICAL APPLICATIO
U
LED CURRENT (mA)
0
EFFICIENCY (%)
75
80
3465 TA04b
70
65
60
55
50 510 15 20
V
IN
= 3.6V
6 LEDS
