LINER LTC3436

LTC3428
4A, 2MHz Dual Phase
Step-Up DC/DC Converter
in 3mm × 3mm DFN
DESCRIPTIO
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FEATURES
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The LTC®3428 is a 2-phase, current mode boost converter, capable of supplying 2A at 5V from a 3.3V input.
Two 93mΩ, 2A N-channel MOSFET switches allow the
LTC3428 to deliver high efficiency from input voltages as
low as 1.6V.
High Efficiency: Up to 92%
2-Phase Control Reduces Output Voltage Ripple
5V at 2A from 3.3V Input
3.3V at 1.5A from 1.8V Input
1.6V to 5.25V Adjustable Output Voltage
1.6V to 4.5V Input Range
Internal Soft-Start Operation
Low Shutdown Current: <1µA
Uses Small Surface Mount Components
10-Pin 3mm × 3mm DFN Package
External parts count and size are minimized by a 1MHz
switching frequency and a 2-phase design. Two phase
operation significantly reduces peak inductor currents
and capacitor ripple current, doubling the effective switching frequency and minimizing inductor and capacitor size.
External compensation allows the feedback loop response
to be optimized for a particular application.
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APPLICATIO S
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Networking Equipment
Handheld Instruments
Digital Cameras
Distributed Power
Local 3.3V to 5V Conversion
Other features include: an active low shutdown pin reduces supply current to below 1µA, internal soft-start,
antiringing control and thermal shutdown. The LTC3428
is available in a low profile (0.75mm) 10-lead (3mm ×
3mm) DFN package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATIO
Efficiency vs Load Current
3.3V to 5V at 2A Converter
95
VIN
3.3V
90
85
VOUT
VIN
OFF ON
SHDN
VC
10k
1000pF
22pF
SWA
LTC3428
AGND
PGNDA
SWB
2.2µH*
VOUT
5V/2A
**
383k
**
80
75
70
65
60
FB
PGNDB
EFFICIENCY (%)
2.2µH*
4.7µF***
121k
22µF****
55
VIN = 3.3V
VOUT = 5V
L = 2.2µH
50
* TOKO FDV06302R2
** PHILIPS PMEG1020
*** TAIYO YUDEN X5R JMK212BJ475MD
**** TAIYO YUDEN X5R JMK316BJ226ML
3428 TA01
45
0.1
1
2
LOAD CURRENT (A)
3428 TA02
3428f
1
LTC3428
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ABSOLUTE
AXI U RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
VIN, VOUT, SWA, SWB Voltage ....................... – 0.3 to 6V
SWA, SWB Voltage, Pulsed, <100ns ......................... 7V
SHDN, VC Voltage ......................................... – 0.3 to 6V
FB Voltage ................................... – 0.3 to (VOUT + 0.3V)
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range ..................–65°C to 125°C
ORDER PART
NUMBER
TOP VIEW
10 PGNDB
PGNDA
1
SWA
2
VOUT
3
SHDN
4
8 VIN
7 AGND
VC
5
6 FB
9 SWB
11
LTC3428EDD
DD PART
MARKING
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
EXPOSED PAD MUST BE SOLDERED
TO GROUND PLANE ON PCB
TJMAX = 125°C, θJA = 45°C/W,
θJC = 3°C/W
LBBG
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 = 3.3V, VOUT = 5V unless otherwise noted.
PARAMETER
CONDITIONS
MIN
Minimum Startup Voltage
Quiescent Current, VOUT
Quiescent Current, VIN
SHDN = VIN
SHDN = VIN
Shutdown Current
SHDN = 0V
Switching Frequency
Per Phase
FB Regulated Voltage
FB Input Current
MAX
1.5
1.6
V
100
1.3
200
2.0
µA
mA
1
µA
0.8
1.0
1.2
●
1.219
1.243
1.268
V
1
50
nA
VFB = 1.24V
170
Output Adjust Voltage
1.6
VSWA, VSWB = 5.5V, Per Phase
NMOS Switch On Resistance
VOUT = 5V, Per Phase
NMOS Current Limit
Per Phase
UNITS
●
Error Amp Transconductance
NMOS Switch Leakage
TYP
0.1
MHz
µS
5.25
V
2.5
µA
0.093
Ω
●
2
2.5
A
●
0.4
0.8
1.5
V
0.01
1
µA
Maximum Duty Cycle
●
80
Minimum Duty Cycle
●
SHDN Input Threshold
SHDN Input Current
Current Limit Delay to Output
(Note 3)
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC3428E 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.
87
%
0
40
%
ns
Note 3: Specification is guaranteed by design and not 100% tested in
production.
Note 4: 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.
3428f
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LTC3428
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TYPICAL PERFOR A CE CHARACTERISTICS
All characteristic curves at TA = 25°C unless otherwise noted.
SW Pin and Inductor Current in
Discontinuous Mode, Demonstrating
Anti-Ring Circuit Operation
SWA, SWB Switching Waveforms
100mV/DIV
2V/DIV
SWA
Transient Response, 0.5A to 1.5A
5V/DIV
SWB
500mA/DIV
500mA/DIV
500ns/DIV
500ns/DIV
100µs/DIV
3428 G01
3428 G02
Output Voltage Ripple with 22µF
Ceramic Capacitor
3428 G03
Switch RDS(ON) vs VOUT
Converter Efficiency
95
108
3.3V TO 5V
106
90
104
50mV/DIV
102
2.5V TO 3.3V
80
RDS(ON) (mΩ)
EFFICIENCY (%)
85
2.5V TO 5V
75
70
100
98
96
94
65
92
60
90
55
0.05
500ns/DIV
0.1
1
88
2.5
2
3.0
LOAD CURRENT (A)
3428 G04
3428 G05
SWA, SWB Rise Time, I = 2A
Switch RDS(ON) vs Temperature
Feedback Voltage vs Temperature
1.27
1.26
100
FB VOLTAGE (V)
RDS(ON) (mΩ)
110
90
80
60
–45 –25 –5
3428 G07
1.25
1.24
1.23
70
10ns/DIV
5.0
3428 G06
120
1V/DIV
4.0
4.5
3.5
OUTPUT VOLTAGE (V)
15 35 55 75
TEMPERATURE (°C)
95 115
3428 G08
1.22
–45 –25
–5
15 35
55 75
TEMPERATURE (°C)
95 115
3428 G09
3428f
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LTC3428
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TYPICAL PERFOR A CE CHARACTERISTICS
Peak Current Limit vs
Temperature
3.4
PEAK CURRENT LIMIT (A)
3.2
3.0
2.8
2.6
2.4
2.2
2.0
–45
–25
35
15
55
–5
TEMPERATURE (°C)
75
95
3428 G10
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PI FU CTIO S
PGNDA, PGNDB (Pins 1, 10, 11 (Exposed Pad)): Power
Ground for the IC. Tie directly to local ground plane.
SWB (Pin 2), SWA (Pin 9): Phase B and Phase A Switch
Pins. The inductor and Schottky diodes for each phase are
connected to these pins. Minimize trace length to reduce
EMI.
VOUT (Pin 3): Power Supply Output and Bootstrapped
Power Source for the IC. Connect low ESR output filter
capacitors from this pin to the ground plane.
SHDN (Pin 4): Shutdown Pin. Grounding this pin shuts
down the IC. Connect to a voltage greater than 1.5V to
enable.
VC (Pin 5): Error Amp Output. A frequency compensation
network is connected to this pin to compensate the boost
converter loop.
FB (Pin 6): Feedback Pin. A resistor divider from VOUT is
connected here to set the output voltage according to
VOUT = 1.243 • (1 + R1 / R2)
AGND (Pin 7): Signal Ground for the IC. Connect to ground
plane near feedback resistor divider.
VIN (Pin 8): Input Supply Pin. Bypass VIN with a low ESR
ceramic capacitor of at least 4.7µF. X5R and X7R dielectrics are preferred for their superior voltage and temperature characteristics.
3428f
4
LTC3428
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BLOCK DIAGRA
FB
FB
ERROR AMPLIFIER/SOFT-START
VIN
–
VC
+
1.243V
VOUT
CURRENT
LIMIT
ISENB
RAMP/
SLOPE COMP
–
–
+
ISENB
SWB
PWM
COMP
PWM
LOGIC
PGNDB
DRIVER
CLK B
CHANNEL B
OSCILLATOR
CHANNEL A
TSD
CLK A
SWA
RAMP/
SLOPE COMP
ISENA
SHDN
PWM
COMP
PGNDA
DRIVER
SHUTDOWN
CURRENT
LIMIT
VC
AGND
+
–
–
PWM
LOGIC
5pF
ISENA
3428 BD
3428f
5
LTC3428
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APPLICATIO S I FOR ATIO
DETAILED DESCRIPTION
The LTC3428 provides high efficiency, low noise power
for high current boost applications. A current mode architecture with adaptive slope compensation provides both
simple loop compensation as well as excellent transient
response. The low RDS(ON) switches provide the pulse
width modulation control at high efficiency.
Oscillator: The per phase switching frequency is internally
set to a nominal value of 1MHz.
Current Sensing: Lossless current sensing converts the
peak current signal to a voltage which is summed with the
internal slope compensation. This summed signal is then
compared with the error amplifier output to provide a peak
current command for the PWM. Slope compensation is
internal to the IC and adapts to changes to the input
voltage, allowing the converter to provide the necessary
degree of slope compensation without causing a loss in
phase margin in the loop characteristic.
Error Amplifier: The error amplifier is a transconductance
amplifier with a transconductance (gm) = 1/7.5kΩ. A
simple compensation network is placed from VC to ground.
The internal 5pF capacitor between VC and ground will
often simplify the external network to a simple R-C combination. The internal 1.243V reference voltage is compared to the voltage on FB to generate an error signal at the
output of the error amplifier (VC). A voltage divider from
VOUT to ground programs the output voltage from 1.6V to
5.25V using the equation:
Anti-Ringing Control: The antiringing control places an
impedance across the inductor of each phase to damp the
high frequency ringing on the SWA, SWB pins during
discontinuous mode operation. The LC ringing on the
switch pin due to the inductor and switch pin capacitance
is low energy, but can cause EMI radiation.
2-Phase Operation
The LTC3428 uses a two-phase architecture, rather than
the conventional single phase architecture used in most
other boost converters. The two phases are spaced 180°
apart. Two phase operation doubles the output ripple
frequency and provides a significant reduction in output
ripple current, minimizing the stress on the output capacitor. Inductor (input) peak and ripple currents are also
reduced, allowing for the use of smaller, lower cost
inductors. The greatly reduced output ripple current also
minimizes the output capacitance requirement. The higher
frequency output ripple is easier to filter for lower noise
applications.
Input and output current comparisons for single and
2-phase converters are illustrated in Figures 1 and 2.
For the example illustrated in Figure 2, peak-to-peak
output ripple current was reduced by 85%, from 4.34A, to
0.64A, and peak inductor current was reduced by 53%,
from 4.34A to 2.02A. These reductions enable the use of
low profile, smaller valued inductors and output capacitors as compared to a single-phase design.
4.4
VOUT = 1.243V • ( 1+ R1/R2)
Current Limit: The current limit comparator in each phase
will shut off the N-channel MOSFET switches once the
current exceeds the current limit threshold, nominally
2.5A. The current limit delay to output is typically 50ns.
The current signal leading edge is blanked for 50ns to
enhance noise rejection.
1 PHASE
CONVERTER
4.2
INPUT CURRENT (A)
Soft-Start: An internal soft-start of approximately 1.5ms
is provided. This is a ramp signal that limits the peak
current until the internal soft-start voltage is greater than
the internal current limit voltage. The internal soft-start
capacitor is automatically discharged when the part is in
shutdown mode.
4.3
4.1
2 PHASE
CONVERTER
4.0
3.9
3.8
3.7
3.6
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
TIME (µs)
3428 F01
Figure 1. Input Ripple Current Comparison
Between Single Phase and Two-Phase Boost
Converters with a 2A Load and 50% Duty Cycle
3428f
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LTC3428
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APPLICATIO S I FOR ATIO
Sumida CDRH4D22C/LD or CDRH5D28 series, Toko
FDV0630 or D62CB series.
5.0
1 PHASE
CONVERTER
OUTPUT (DIODE) CURRENT (A)
4.5
4.0
Table 1. Inductor Vendor Information
3.5
Supplier Phone
3.0
2 PHASE
CONVERTER
2.5
2.0
www.coilcraft.com
Murata
USA:
USA:
(814) 238-1431 (814) 238-0490
www.murata.com
Sumida
USA:
(847) 956-6666
Japan:
81-3-3607-5111
www.sumida.com
TDK
(847) 803-6100 (847) 803-6296
www.component.tdk.com
Toko
(847) 299-0070 (847) 699-7864
www.toko.com
Wurth
(201)785-8800
www.we-online.com
0.5
0
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
TIME (µs)
3428 F02
Figure 2. Output Ripple Current Comparison
Between Single Phase and Two Phase Boost
Converters with a 2A Load and 50% Duty Cycle
Website
(847) 639-6400 (847) 639-1469
1.5
1.0
Fax
Coilcraft
USA:
(847) 956-0702
Japan:
81-3-3607-5144
(201)785-8810
Output Capacitor Selection
COMPONENT SELECTION
Inductor Selection
The high frequency operation of the LTC3428 allows for
the use of small surface mount inductors. The inductor
ripple current is typically set to between 20% and 40% of
the maximum inductor current. For a given set of conditions, the inductance is given as follows:
L≥
VIN(MIN) • (VOUT – VIN(MIN) )
, L > 2µH
R • VOUT
where:
R = Allowable inductor current ripple (Amps P-P)
VIN(MIN) = Minimum input voltage (V)
VOUT = Output voltage (V)
For high efficiency, the inductor should have a high
frequency core material, such as ferrite, to reduce core
losses. The inductor should have a low ESR (equivalent
series resistance) to reduce I2R losses and must be able
to handle the peak inductor current without saturating.
Use of a toroid, pot core, or shielded bobbin inductor will
minimize radiated noise. See Table 1 for a list of inductor
manufacturers. Some example inductor part types are:
Coilcraft 1608 and 3316 series, Murata LQH55D series,
The minimum value of the capacitor is set to reduce the
output ripple voltage due to charging and discharging the
capacitor each cycle. The steady state ripple due to this
charging is given by:
VRIPPLE(C) =
1 IPEAK • (VOUT – VIN(MIN) )
•
2
COUT • VOUT • f
where: IPEAK = Peak inductor current (A)
The equivalent series resistance (ESR) of the output
capacitor will contribute another term to output voltage
ripple. Ripple voltage due to capacitor ESR is:
VRIPPLE(ESR) = IPEAK • RESR(C)
where:
RESR(C) = Capacitor ESR
The ESL (Equivalent Series Inductance) is another
capacitor characteristic that needs to be minimized. ESL
will be minimized by using small surface mount ceramic
capacitors, placed as close to the VOUT pin as possible.
Input Capacitor Selection
Since the VIN pin directly powers most of the internal
circuitry, it is recommended to place at least a 4.7µF, low
ESR bypass capacitor between VIN and AGND, as close to
the IC as possible. See Table 2 for a list of capacitor
manufacturers.
3428f
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LTC3428
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APPLICATIO S I FOR ATIO
Table 2. Capacitor Vendor Information
Supplier
Phone
Fax
Website
AVX
(803) 448-9411 (803) 448-1943 www.avxcorp.com
Sanyo
(619) 661-9322 (619) 661-1055 www.sanyovideo.com
TDK
(847) 803-6100 (847) 803-6296 www.component.tdk.com
Murata
(814) 237-1431 (814) 238-0490 www.murata.com
Taiyo Yuden (408) 573-4150 (408) 573-4159 www.t-yuden.com
Output Diode Selection
For high efficiency, a fast switching diode with low reverse
leakage and a low forward drop is required. Schottky diodes
are recommended for their low forward drop and fast
switching times. When selecting a diode, it is important to
remember that the average diode current in a boost
converter is equal to the average load current: ID = ILOAD
When selecting a diode, make sure that the peak
forward current and average power dissipation ratings
meet the application requirements. See Table 3 for a list
of Schottky diode manufacturers. Example diodes are
Philips PMEG1020, PMEG2010, On-Semi MBRA210, IR
10BQ015, Microsemi UPS120E, UPS315.
If the junction temperature gets too high, the LTC3428 will
stop all switching until the junction temperature drops to
safe levels. The typical over temperature threshold is
150°C.
Closing the Feedback Loop
The LTC3428 uses current mode control with internal,
adaptive slope compensation. Current mode control eliminates the 2nd order pole in the loop response of voltage
mode converters due to the inductor and output capacitor,
simplifying it to a single pole response. The product of the
modulator control to output DC gain and the error amp
open-loop gain equals the DC gain of the system.
G DC = G CONTROL • G EA •
G CONTROL =
Phone
Philips
+31 40 27 24825
Microsemi
(949) 221-7100
On-Semi
(602) 244-6600
International (310) 469-2161
Rectifier
Fax
Website
2 • VIN
IOUT
G EA ≈ 100
The output filter pole is given by:
Table 3. Diode Vendor Information
Supplier
VREF
VOUT
IOUT
Hz
π • VOUT • C OUT
fPOLE =
www.philips.com
(949)756-0308
www.microsemi.com
www.onsemi.com
(310) 322-3332
where COUT is the output filter capacitor value. The output
filter zero is given by:
www.irf.com
Thermal Considerations
To deliver maximum power, it is necessary to provide a
good thermal path to dissipate the heat generated within
the LTC3428’s package. The large thermal pad on the IC
underside can accomplish this requirement. Use multiple
PC board vias to conduct heat from the IC and to a copper
plane that has as much area as possible.
fZERO =
1
2 • π • RESR • C OUT
Hz
where RESR is the output capacitor equivalent series
resistance.
A complication of the boost converter topology is the right
half plane (RHP) zero and is given by:
2
fRHP =
VIN • RO
2 • π • L • VO
2
Hz
3428f
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LTC3428
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APPLICATIO S I FOR ATIO
This zero causes a gain increase with phase lag. With
heavy loads, this can occur at a relatively low frequency.
For this reason, loop gain is typically rolled off below the
RHP zero frequency.
VOUT
+
–
1
2 • π • 400e 6 • C C1
1
fZERO1 ≈
2 • π • RZ • C C1
1
fZERO2 ≈
2 • π • RZ • (C C2 + 5pF )
R1
FB
R2
A typical error amp compensation is shown in Figure 3 and
in the Typical Application section.
The equations for the loop dynamics are as follow:
1.243V
VC
5pF
RZ
CC2
CC1
fPOLE1 ≈
3428 F03
Figure 3.
3428f
9
LTC3428
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TYPICAL APPLICATIO S
2.5V to 3.3V at 2.5A Converter
2.5VIN
4.7µH*
8
4
SHUTDOWN
5
10k
22pF
7
1
1000pF
4.7µF
VIN
LTC3428
VOUT
SHDN
SWA
VC
SWB
AGND
PGNDA
FB
PGNDB
4.7µH*
3
VOUT
3.3V, 2.5A
2
**
9
**
205k
6
10
4.7µF***
4×
* TOKO DC53LC
** MICROSEMI UPS120E
*** TAIYO YUDEN X5R JMK212BJ475MD
121k
3428 TA03
3428f
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LTC3428
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PACKAGE DESCRIPTIO
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115
TYP
6
0.38 ± 0.10
10
0.675 ±0.05
3.50 ±0.05
1.65 ±0.05
2.15 ±0.05 (2 SIDES)
3.00 ±0.10
(4 SIDES)
PACKAGE
OUTLINE
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
(DD10) DFN 1103
5
0.200 REF
0.25 ± 0.05
0.50
BSC
2.38 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
1
0.25 ± 0.05
0.50 BSC
0.75 ±0.05
0.00 – 0.05
2.38 ±0.10
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
3428f
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.
11
LTC3428
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3A, 3MHz Synchronous Boost Converter
with Output Disconnect
96% Efficiency, VIN: 0.5V to 4.5V, VOUT(MAX) = 5.5V, IQ = 12µA,
ISD <1µA, QFN-24 Package
LTC3425
5A (ISW), 8MHz, 4-Phase Synchronous Step-Up
DC/DC Converter
95% Efficiency, VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12µA,
ISD <1µA, QFN-32 Package
LTC3429
600mA, 500kHz Synchronous Boost Converter
with Output Disconnect
96% Efficiency, VIN: 0.5V to 4.4V, VOUT(MAX) = 5.5V, IQ = 20µA,
ISD <1µA, ThinSOT Package
LTC3436
3A (ISW), 1MHz, 34V Step-Up DC/DC Converter
VIN: 3V to 25V, VOUT(MAX) = 34V, IQ = 0.9mA,
ISD <6µA, TSSOP-16E Package
LTC3459
10V Micropower Synchronous Boost Converter
85% Efficiency, VIN: 1.5V to 5.5V, VOUT(MAX) = 10V, IQ = 10µA,
ISD <1µA, ThinSOT Package
LT3464
85mA (ISW), High Efficiency Step-Up DC/DC Converter
with Integrated Schottky and PNP Disconnect
VIN: 2.3V to 10V, VOUT(MAX) = 34V, IQ = 25µA,
ISD <1µA, ThinSOT Package
No RSENSE is a registered trademark of Linear Technology Corporation.
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Linear Technology Corporation
LT/TP 0804 1K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
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FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2004