FEATURES
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LT3460/LT3460-1
1.3 MHz/650kHz Step-Up
DC/DC Converter in SC70,
ThinSOT and DFN
DESCRIPTION
The LT
®
3460/LT3460-1 are general purpose step-up DC/
DC converters. The LT3460/LT3460-1 switch at 1.3MHz/
650kHz, allowing the use of tiny, low cost and low height
capacitors and inductors. The constant frequency results
in low, predictable output noise that is easy to filter.
The high voltage switches in the LT3460/LT3460-1 are
rated at 38V, making the device ideal for boost converters
up to 36V. The LT3460 can generate 12V at up to 70mA
from a 5V supply.
The low 1mA quiescent current and 650kHz switching
frequency of LT3460-1 make it ideal for lower current
applications.
The LT3460 is available in SC70 and SOT-23 packages.
The LT3460-1 is available in SC70 and 2mm × 2mm DFN
packages.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation. ThinSOT is
a trademark of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
1.3MHz (LT3460) Switching Frequency
650kHz (LT3460-1) Switching Frequency
High Output Voltage: Up to 36V
300mA Integrated Switch (LT3460)
180mA Integrated Switch (LT3460-1)
Wide Input Range: 2.5V to 16V
Uses Small Surface Mount Components
Low Shutdown Current: <1μA
Low Profile (1mm) SC70 (LT3460 and LT3460-1),
SOT-23 (ThinSOT™) (LT3460) and 2mm × 2mm DFN
(LT3460-1) Packages
APPLICATIONS
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Digital Cameras
CCD Bias Supply
XDSL Power Supply
TFT-LCD Bias Supply
Local 5V or 12V Supply
Medical Diagnostic Equipment
Battery Backup
TYPICAL APPLICATION
EFFICIENCY (%)
Efficiency
90
85
80
75
70
65
60
5V to 12V, 70mA Step-Up DC/DC Converter
V
IN
5V
4.7μF
V
IN
LT3460
OFF ON
SHDN
GND
FB
15k
1μF
22μH
V
OUT
12V
70mA
SW
130k
22pF
0
20
40
60
LOAD CURRENT (mA)
80
3460 F01a
Switching Waveforms
3460 F01
V
SW
5V/DIV
I
L
100mA/DIV
0.2μs/DIV
3460 F01b
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LT3460/LT3460-1
ABSOLUTE MAXIMUM RATINGS
Input Voltage (V
IN
) ....................................................16V
SW Voltage ...............................................................38V
FB Voltage ...................................................................5V
SHDN Voltage ...........................................................16V
(Note 1)
Operating Ambient
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
PIN CONFIGURATION
TOP VIEW
SW 1
GND 2
FB 3
4
SHDN
5 V
IN
SW 1
GND 2
FB 3
TOP VIEW
6 V
IN
5 GND
4
SHDN
S5 PACKAGE
5-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
TOP VIEW
FB 1
NC 2
SW 3
7
6
SHDN
5 NC
4 V
IN
SC6 PACKAGE
6-LEAD PLASTIC SC70
T
JMAX
= 125°C,
θ
JA
= 400°C/W IN FREE AIR
θ
JA
= 270°C/W ON BOARD OVER GROUND PLANE
DC PACKAGE
6-LEAD (2mm × 2mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 102°C/W
EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LT3460ES5#PBF
LT3460ESC6#PBF
LT3460ESC6-1#PBF
LT3460EDC-1#PBF
TAPE AND REEL
LT3460ES5#TRPBF
LT3460ESC6#TRPBF
LT3460ESC6-1#TRPBF
LT3460EDC-1#TRPBF
PART MARKING
LTB1
LAAF
LDJV
LDNB
PACKAGE DESCRIPTION
5-Lead Plastic TSOT-23
6-Lead Plastic SC70
6-Lead Plastic SC70
6-Lead (2mm × 2mm) Plastic DFN
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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/
3460fb
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LT3460/LT3460-1
ELECTRICAL CHARACTERISTICS
PARAMETER
Minimum Operating
Voltage
Maximum Operating
Voltage
Feedback Voltage
Feedback Line Regulation
FB Pin Bias Current
Supply Current
Switching Frequency
Maximum Duty Cycle
Switch Current Limit
Switch V
CESAT
Switch Leakage Current
SHDN
Voltage High
SHDN
Voltage Low
SHDN
Pin Bias Current
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.
40
I
SW
= 250mA (LT3460), I
SW
= 100mA (LT3460-1)
V
SW
= 5V
1.5
0.4
15
SHDN
= 0V
1.0
85
300
2.5V < V
IN
< 16V
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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
= 3V, V
SHDN
= 3V, unless otherwise noted.
LT3460
LT3460-1
CONDITIONS
MIN
2.5
16
1.235
1.225
5
1.255
0.015
25
2.0
0.1
1.3
90
420
320
0.01
600
450
1
1.5
0.4
80
3.0
0.5
1.7
0.35
80
180
0
1.275
1.280
1.235
1.225
1.255
0.015
25
1.0
0.1
0.65
90
260
220
0.01
380
350
1
80
1.5
0.5
1.0
TYP
MAX
MIN
2.5
16
1.275
1.280
TYP
MAX
UNITS
V
V
V
V
%/V
nA
mA
μA
MHz
%
mA
mV
μA
V
V
μA
Note 2:
The LT3460E/LT3460-1E is guaranteed to meet 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.
TYPICAL PERFORMANCE CHARACTERISTICS
Quiescent Current
2.5
–50°C
2.0
100°C
I
Q
(mA)
1.5
LT3460-1
LT3460
SWITCHING FREQUENCY (MHz)
SHDN
PIN BIAS CURRENT (μA)
1.2
1.0
0.8
0.6
0.4
0.2
0
0
5
V
IN
(V)
3460 G01
Switching Frequency
1.4
LT3460
400
350
300
250
200
150
SHDN
Pin Bias Current
SHDN
= 16V (LT3460)
1.0
25°C
LT3460-1
0.5
SHDN
= 16V (LT3460-1)
100
SHDN
= 3V (LT3460-1)
50
SHDN
= 3V (LT3460)
–25
50
25
0
TEMPERATURE (°C)
75
100
3460 G03
10
15
0
–50
–25
50
25
0
TEMPERATURE (°C)
75
100
3460 G02
0
–50
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LT3460/LT3460-1
TYPICAL PERFORMANCE CHARACTERISTICS
Feedback Bias Current
30
FEEDBACK BIAS CURRENT (nA)
25
1.255
20
V
FB
(V)
15
10
1.245
5
0
–50
1.240
–50
1.250
1.260
Feedback Voltage
–25
50
25
0
TEMPERATURE (°C)
75
100
3460 G04
–25
50
25
0
TEMPERATURE (°C)
75
100
3460 G05
Switch Saturation Voltage
(V
CESAT
)
400
350
300
V
CESAT
(mV)
250
200
150
100
50
0
–50
–25
50
25
0
TEMPERATURE (°C)
75
100
3460 G06
Current Limit vs Duty Cycle
450
400
350
CURRENT LIMIT (mA)
LT3460
I
C
= 250mA
I
C
= 200mA
(LT3460)
(LT3460)
300
250
200
150
100
50
0
0
0.2
0.6
0.4
DUTY CYCLE
I
C
= 50mA
(LT3460-1)
(LT3460)
I
C
= 100mA
LT3460-1
0.8
1.0
3460 G07
PIN FUNCTIONS
(ThinSOT/SC70/DFN Packages)
SW (Pin 1/Pin 1/Pin 3):
Switch Pin. Connect inductor/diode
here. Minimize trace at this pin to reduce EMI.
GND (Pin 2/Pins 2 and 5/Exposed Pad Pin 7):
Ground
Pin. Tie directly to local ground plane.
FB (Pin 3/Pin 3/Pin 1):
Feedback Pin. Reference
voltage is 1.255V. Connect resistor divider tap here.
Minimize trace area at FB. Set V
OUT
according to
V
OUT
= 1.255V (1 + R1/R2).
SHDN
(Pin 4/Pin 4/Pin 6):
Shutdown Pin. Tie to 1.5V or
higher to enable device; 0.4V or less to disable device.
Also functions as soft-start. Use RC filter (47k, 47nF typ)
as shown in Figure 1.
V
IN
(Pin 5/Pin 6/Pin 4):
Input Supply Pin. Must be locally
bypassed.
NC (NA/NA/Pins 2, 5):
No-Connects. These pins are not
connected to internal circuitry. They should be tied to
ground to improve thermal and electrical performance.
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LT3460/LT3460-1
BLOCK DIAGRAM
V
IN
V
OUT
R1 (EXTERNAL)
FB
R2 (EXTERNAL)
FB
C
C
1.255V
REFERENCE
+
A1
COMPARATOR
SW
DRIVER
–
R
C
A2
R
S
Q
–
Q1
+
+
0.1Ω
–
SHUTDOWN
R
S
(EXTERNAL)
SHDN
C
S
(EXTERNAL)
R
S
, C
S
OPTIONAL SOFT-START COMPONENTS
1.3MHz
OSCILLATOR
GND
3460 BD
RAMP
GENERATOR
Figure 1. Block Diagram, LT3460
OPERATION
The LT3460/LT3460-1 uses a constant frequency, current
mode control scheme to provide excellent line and load
regulation. Operation can be best understood by referring to
the block diagram in Figure 1. 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 1.255V.
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.
Feedback Loop Compensation
The LT3460/LT3460-1 has an internal feedback compensa-
tion network as shown in Figure 1 (R
C
and C
C
). However,
because the small signal characteristics of a boost converter
change with operation conditions, the internal compensa-
tion network cannot satisfy all applications. A properly
designed external feed forward capacitor from V
OUT
to
FB (C
F
in Figure 2) will correct the loop compensation for
most applications.
The LT3460/LT3460-1 uses peak current mode control.
The current feedback makes the inductor very similar
to a current source in the medium frequency range. The
power stage transfer function in the medium frequency
range can be approximated as:
G
P(s)
=
K1
s • C2
,
where C2 is the output capacitance, and K1 is a constant
based on the operating point of the converter. In continuous
current mode, K1 increases as the duty cycle decreases.
The internal compensation network R
C
, C
C
can be ap-
proximated as follows in medium frequency range:
G
C(s)
=K2
•
The zero
f
Z
=
1
2 • • R
C
• C
C
s • R
C
• C
C
+
1
s • C
C
is about 70kHz.
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