LINER LT3461A 1.3mhz/3mhz step-up dc/dc converters with integrated schottky in thinsot Datasheet

LT3461/LT3461A
1.3MHz/3MHz Step-Up
DC/DC Converters with
Integrated Schottky in ThinSOT
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FEATURES
DESCRIPTIO
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The LT®3461/LT3461A are general purpose fixed frequency current mode step-up DC/DC converters. Both
devices feature an integrated Schottky and a low VCESAT
switch allowing a small converter footprint and lower parts
cost. The LT3461 switches at 1.3MHz while the LT3461A
switches at 3MHz. These high switching frequencies enable the use of tiny, low cost and low height capacitors and
inductors. The constant switching frequency results in
predictable output noise that is easy to filter, and the
inductor based topology ensures an input free from switching noise typically present with charge pump solutions.
The high voltage switch in the LT3461/LT3461A is rated at
40V making the device ideal for boost converters up to
38V.
■
■
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■
■
■
■
■
■
■
Integrated Schottky Rectifier
Fixed Frequency 1.3MHz/3MHz Operation
High Output Voltage: Up to 38V
Low VCESAT Switch: 260mV at 250mA
12V at 70mA from 5V Input
5V at 115mA from 3.3V Input
Wide Input Range: 2.5V to 16V
Uses Small Surface Mount Components
Low Shutdown Current: <1µA
Soft-Start
Low Profile (1mm) SOT-23 (ThinSOTTM) Package
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APPLICATIO S
■
■
■
■
■
■
Digital Cameras
CCD Bias Supply
XDSL Power Supply
TFT-LCD Bias Supply
Local 5V or 12V Supply
Medical Diagnostic Equipment
Battery Backup
The LT3461/LT3461A are available in a low profile (1mm)
SOT-23 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
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■
TYPICAL APPLICATIO
5V to 12V, 70mA Step-Up DC/DC Converter
C1
1µF
OFF ON
L1
10µH
1
SW
6
5
VIN
VOUT
LT3461A
4
3
SHDN
FB
GND
2
80
261k
30.1k
15pF
VOUT
12V
70mA
C2
1µF
VIN = 5V
EFFICIENCY (%)
VIN
5V
Efficiency
85
75
VIN = 3.3V
70
65
3461 TA01a
60
0
20
60
40
LOAD CURRENT (mA)
80
3461 TAO1b
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LT3461/LT3461A
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ABSOLUTE
AXI U RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
Input Voltage (VIN) .................................................. 16V
VOUT, SW Voltage .................................................... 40V
FB Voltage ................................................................. 5V
SHDN Voltage .......................................................... 16V
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
ORDER PART
NUMBER
TOP VIEW
SW 1
GND 2
FB 3
6 VIN
LT3461AES6
LT3461ES6
5 VOUT
4 SHDN
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
TJMAX = 125°C,
θJA = 150°C ON BOARD OVER
GROUND PLANE,
θJC = 120°C/W
S6 PART MARKING
LTAHG
LTAEB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, VIN = 3V, VSHDN = 3V, unless otherwise noted.
PARAMETER
CONDITIONS
MIN
Minimum Operating Voltage
TYP
Feedback Voltage
●
1.235
1.225
Feedback Line Regulation
1.255
16
V
1.275
1.280
V
V
0.005
●
FB Pin Bias Current
FB = 1.3V, Not Switching
SHDN = 0V
UNITS
V
Maximum Operating Voltage
Supply Current
MAX
2.5
%/V
40
100
nA
2.8
0.1
3.6
0.5
mA
µA
Switching Frequency (LT3461A)
●
2.1
3.0
3.9
MHz
Switching Frequency (LT3461)
●
1.0
1.3
1.7
MHz
Maximum Duty Cycle (LT3461A)
●
82
%
Maximum Duty Cycle (LT3461)
●
92
%
Switch Current Limit
420
600
mA
Switch VCESAT
ISW = 250mA
300
260
350
mV
Switch Leakage Current
VSW = 5V
0.01
1
µA
Schottky Forward Voltage
ISCHOTTKY = 250mA
800
1100
mV
Schottky Reverse Leakage
VOUT – SW = 40V
0.03
4
µA
SHDN Voltage High
1.5
V
SHDN Voltage Low
SHDN Pin Bias Current
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
35
0.4
V
50
µA
Note 2: The LT3461E/LT3461AE 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.
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LT3461/LT3461A
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TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency (LT3461)
Current Limit
1.6
FB Pin Voltage
1.28
480
TA = 25°C
1.27
1.4
1.3
1.2
360
FB VOLTAGE (V)
CURRENT LIMIT (mA)
FREQUENCY (MHz)
1.5
240
1.26
1.25
1.24
120
1.1
1.23
1.0
–40 –20
40
20
60
0
TEMPERATURE (°C)
80
0
10
100
20
30
40 50 60 70
DUTY CYCLE (%)
80
3461a G01
1.22
–40 –20
90
480
320
TA = 25°C
3.0
2.7
2.4
280
SHDN PIN CURRENT (µA)
CURRENT LIMIT (mA)
FREQUENCY (MHz)
TA = 25°C
420
3.6
360
300
240
180
120
60
2.1
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
80 100
100
SHDN Pin Current
Current Limit in Soft-Start Mode
Oscillator Frequency (LT3461A)
80
3461a G03
3461a G02
3.9
3.3
40
20
60
0
TEMPERATURE (°C)
0
1.3
240
200
160
120
80
40
1.5
0
1.7
2.1
1.9
SHDN PIN VOLTAGE (V)
2.3
0
4
8
12
3461a G06
3461a G05
3461a G04
16
SHDN PIN VOLTAGE (V)
Switching Waveform
Circuit of Figure 4
Load Transient Response
Circuit of Figure 4
ILOAD
70mA
35mA
VSW
5V/DIV
VOUT
100mV/DIV
VOUT
50mV/DIV
ILOAD = 60mA
0.2µs/DIV
3461a G08
50µs/DIV
3461a G09
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LT3461/LT3461A
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PI FU CTIO S
SW (Pin 1): Switch Pin. Connect inductor here. Minimize
trace at this pin to reduce EMI.
SHDN (Pin 4): 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.
GND (Pin 2): Ground Pin. Tie directly to local ground
plane.
VOUT (Pin 5): Output Pin. Connect to resistor divider. Put
capacitor close to pin and close to GND plane.
FB (Pin 3): Feedback Pin. Reference voltage is 1.255V.
Connect resistor divider tap here. Minimize trace area at
FB. Set VOUT according to VOUT = 1.255V (1 + R1/R2).
VIN (Pin 6): Input Supply Pin. Must be locally bypassed.
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BLOCK DIAGRA
1.255V
REFERENCE
VIN 6
–
5 VOUT
Q
Q1
S
+
CC
3 FB
FB
R
A2
RC
R1 (EXTERNAL)
SW
DRIVER
–
A1
VOUT
1
COMPARATOR
+
+
R2 (EXTERNAL)
∑
0.1Ω
–
SHUTDOWN
RS (EXTERNAL)
4 SHDN
RAMP
GENERATOR
CS (EXTERNAL)
RS, CS OPTIONAL SOFT-START COMPONENTS
3MHz*
OSCILLATOR
2
*LT3461 IS 1.3MHz
GND
3461a F02
Figure 1. Block Diagram
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OPERATIO
Layout Hints
The high speed operation of the LT3461/LT3461A demands careful attention to board layout. You will not get
advertised performance with careless layout. Figure 2
shows the recommended component placement.
C1
+
GND
L1
VIN
R2
+
The LT3461/LT3461A 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.
R1
C2
VOUT
SHUTDOWN
C3
3461a F03
Figure 2. Suggested Layout
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LT3461/LT3461A
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APPLICATIO S I FOR ATIO
The LT3461 has a built-in Schottky diode. When supply
voltage is applied to the VIN pin, the voltage difference
between VIN and VOUT generates inrush current flowing
from input through the inductor and the Schottky diode to
charge the output capacitor. The maximum nonrepetitive
surge current the Schottky diode in the LT3461 can
sustain is 1.5A. The selection of inductor and capacitor
value should ensure the peak of the inrush current to be
below 1.5A. In addition, turn-on of the LT3461 should be
delayed until the inrush current is less than the maximum
current limit. The peak inrush current can be calculated as
follows:
numbers can be expected if the LT3461 is supplied from a
separate low voltage rail.
160
VIN = 5V
VIN = 8V
VIN = 12V
120
VIN >15V
IOUT (mA)
Inrush Current
80
40
0
6
14
22
30
38
VOUT (V)
3461 F01a
⎞
⎛
⎜
π ⎟⎟
V – 0.6
• exp ⎜ −
IP = IN
⎟
⎜
L
L
–1
− 1⎟
⎜ 2
⎠
⎝
C
C
Figure 3a. LT3461 Operating Region
160
VIN = 5V
where L is the inductance, r is the resistance of the
inductor and C is the output capacitance.
Table 3 gives inrush peak currents for some component
selections.
IOUT (mA)
120
VIN = 8V
VIN = 12V
VIN >15V
80
40
Table 3. Inrush Peak Current
VIN (V)
L (µH)
C (µF)
IP (A)
5
4.7
1
1.1
5
10
1
0.9
0
6
14
22
30
38
VOUT (V)
3461 F01b
Figure 3b. LT3461A Operating Region
Thermal Considerations
Significant power dissipation can occur on the LT3461
and LT3461A, particularly at high input voltage. Device
load, voltage drops in the power path components, and
switching losses are the major contributors. It is important to measure device power dissipation in an application
to ensure that the LT3461 does not exceed the absolute
maximum operating junction temperature of 125°C over
the operating ambient temperature range. Generally, for
supply voltages below 5V the integrated current limit
function provides adequate protection for nonfault conditions. For supply voltages above 5V, Figures 3a and 3b
show the recommended operating region of the LT3461
and LT3461A, respectively. These graphs are based
on 250mW on-chip dissipation. Improvement of these
Switching Frequency
The key difference between the LT3461 and LT3461A is the
faster switching frequency of the LT3461A. At 3MHz, the
LT3461A switches at twice the rate of the LT3461. The
higher switching frequency of the LT3461A allows physically smaller inductors and capacitors to be used in a given
application, but with a slight decrease in efficiency and
maximum output current when compared to the LT3461.
Generally if efficiency and maximum output current are
crucial, or a high output voltage is being generated, the
LT3461 should be used. If application size and cost are
more important, the LT3461A will be the better choice.
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LT3461/LT3461A
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APPLICATIO S I FOR ATIO
Inductor Selection
The inductors used with the LT3461/LT3461A should
have a saturation current rating of 0.3A or greater. If the
device is used in an application where the input supply will
be hot-plugged, then the saturation current rating should
be equal to or greater than the peak inrush current. For the
LT3461, an inductor value between 10µH and 47µH,
depending upon output voltage, will usually be the best
choice for most designs. For the LT3461A, inductor values
between 4.7µH and 15µH inductor will suffice for most
applications. For best loop stability results, the inductor
value selected should provide a ripple current of 70mA or
more. For a given VIN and VOUT the inductor value to use
with LT3461A is estimated by the formula:
L (in microhenries) =
D • VIN • VOUT • 1sec
1A • 1V
VOUT + 1V – VIN
where D =
VOUT + 1V
Use twice this value for the LT3461.
Capacitor Selection
Low ESR capacitors should be used at the output to
minimize the output voltage ripple. Multilayer ceramic
capacitors using X5R/X7R dielectrics are preferred as they
have a low ESR and maintain capacitance over wide
voltage and temperature range. A 2.2µF output capacitor
is sufficient for most applications using the LT3461, while
a 1µF capacitor is sufficient for most applications using
the LT3461A. High output voltages typically require less
capacitance for loop stability. Always use a capacitor with
sufficient voltage rating.
Either ceramic or solid tantalum capacitors may be used
for the input decoupling capacitor, which should be placed
as close as possible to the LT3461/LT3461A. A 1µF
capacitor is sufficient for most applications.
Phase Lead Capacitor
A small value capacitor can be added across resistor R1
between the output and the FB pin to reduce output
perturbation due to a load step and to improve transient
response. This phase lead capacitor introduces a polezero pair to the feedback that boosts phase margin near
the cross-over frequency. The following formula is useful
to estimate the capacitor value needed:
C PL =
500kΩ
• 1pF
R2
For an application running 50µA in the feedback divider,
capacitor values from 10pF to 22pF work well.
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TYPICAL APPLICATIO S
L1
10µH
VIN
5V
CONTROL
SIGNAL
C1
1µF
47k
47nF
1
SW
5
VIN
VOUT
LT3461A
4
3
SHDN
FB
GND
2
Input Current and Output Voltage
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C1, C2: TAIYO YUDEN EMK212BJ105
L1: MURATA LQH32CN100K53
R1
261k
R2
30.1k
15pF
VOUT
12V
70mA
C2
1µF
3461a TA02a
Figure 4. 5V to 12V with Soft-Start Circuit (LT3461A)
CONTROL
SIGNAL
5V/DIV
IIN
50mA/DIV
VOUT
5V/DIV
1ms/DIV
3461a TA02b
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LT3461/LT3461A
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TYPICAL APPLICATIO S
3.3V to 5V Step-Up Converter Efficiency
80
3.3V to 5V Step-Up Converter (LT3461A)
L1
4.7µH
VIN
3.3V
C1
1µF
OFF ON
R1
45.3k
EFFICIENCY (%)
75
1
SW
6
5
VIN
VOUT
LT3461A
4
3
SHDN
FB
GND
2
VOUT
5V
115mA
15pF
C2
1µF
R2
15k
C1, C2: TAIYO YUDEN X7R LMK212BJ105
L1: MURATA LQH32CN4R7M33 OR EQUIVALENT
70
65
3461a TA03a
60
0
30
60
90
LOAD CURRENT (mA)
120
3461a TA03b
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PACKAGE DESCRIPTIO
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
0.62
MAX
2.90 BSC
(NOTE 4)
0.95
REF
1.22 REF
1.4 MIN
3.85 MAX 2.62 REF
2.80 BSC
1.50 – 1.75
(NOTE 4)
PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.30 – 0.45
6 PLCS (NOTE 3)
0.95 BSC
0.80 – 0.90
0.20 BSC
0.01 – 0.10
1.00 MAX
DATUM ‘A’
0.30 – 0.50 REF
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
0.09 – 0.20
(NOTE 3)
1.90 BSC
S6 TSOT-23 0302
3461af
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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LT3461/LT3461A
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TYPICAL APPLICATIO S
Low Profile (1mm) 3.3V to 15V Step-Up Converter
3.3V to 15V Efficiency
L1
10µH
C1
1µF
OFF ON
1
SW
5
VIN
VOUT
LT3461A
4
3
SHDN
FB
GND
2
70
VOUT
15V
25mA
6
332k
EFFICIENCY (%)
VIN
3.3V
75
22pF
C2
2.2µF
30.1k
C1: TAIYO YUDEN LMK107BJ105KA
C2: TAIYO YUDEN EMK316BJ225KD (X5R)
L1: MURATA LQH2MCN100K02
3461a TA04a
65
60
55
50
0
5
5V to 36V Step-Up Converter (LT3461)
10
15
20
LOAD CURRENT (mA)
25
30
3461a TA04b
5V to 36V Efficiency
80
L1
47µH
C1
1µF
OFF ON
1
SW
6
5
VIN
VOUT
LT3461
4
3
SHDN
FB
GND
2
75
280k
22pF
VOUT
36V
18mA
EFFICIENCY (%)
VIN
5V
C2
0.47µF
50V
10k
C1: TAIYO YUDEN X7R LMK212BJ105
C2: MURATA GRM42-6X7R474K50
L1: MURATA LQH32CN470
70
65
60
55
3461 TA05a
50
0
2
4
6
8
10
12
14
16
18
LOAD CURRENT (mA)
3461 TA05b
3.3V to ±5V Dual Output Converter
C3
1µF
L1
4.7µH
VIN
3.3V
1
SW
5
VIN
VOUT
LT3461A
4
3
SHDN
FB
GND
2
VOUT
5V
100mA
6
C1
1µF
OFF ON
45.3k
15pF
C2
1µF
15k
D1
C1, C2, C3, C4: TAIYO YUDEN JMK107BJ105
D1, D2: PHILIPS PMEG2005EB
L1: MURATA LQH2MCN4R7M02
D2
C4
1µF
10Ω
–5V
15mA
3461 TA06
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DESCRIPTION
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LT3465/LT3465A
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3461af
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Linear Technology Corporation
LT/TP 1004 1K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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